diff --git a/.idea/libraries/Dart_Packages.xml b/.idea/libraries/Dart_Packages.xml
index 65a4c4d..ebfceed 100644
--- a/.idea/libraries/Dart_Packages.xml
+++ b/.idea/libraries/Dart_Packages.xml
@@ -5,174 +5,190 @@
         <entry key="async">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/async-2.0.8/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/async-2.8.1/lib" />
             </list>
           </value>
         </entry>
         <entry key="async_loader">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/async_loader-0.1.2/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/async_loader-0.1.2/lib" />
             </list>
           </value>
         </entry>
         <entry key="boolean_selector">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/boolean_selector-1.0.4/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/boolean_selector-2.1.0/lib" />
+            </list>
+          </value>
+        </entry>
+        <entry key="characters">
+          <value>
+            <list>
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/characters-1.1.0/lib" />
             </list>
           </value>
         </entry>
         <entry key="charcode">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/charcode-1.1.2/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/charcode-1.3.1/lib" />
+            </list>
+          </value>
+        </entry>
+        <entry key="clock">
+          <value>
+            <list>
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/clock-1.1.0/lib" />
             </list>
           </value>
         </entry>
         <entry key="collection">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/collection-1.14.11/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/collection-1.15.0/lib" />
             </list>
           </value>
         </entry>
         <entry key="cupertino_icons">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/cupertino_icons-0.1.2/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/cupertino_icons-0.1.2/lib" />
             </list>
           </value>
         </entry>
-        <entry key="flutter">
+        <entry key="fake_async">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/packages/flutter/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/fake_async-1.2.0/lib" />
             </list>
           </value>
         </entry>
-        <entry key="flutter_test">
+        <entry key="flutter">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/packages/flutter_test/lib" />
+              <option value="$USER_HOME$/Development/flutter/packages/flutter/lib" />
             </list>
           </value>
         </entry>
-        <entry key="matcher">
+        <entry key="flutter_test">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/matcher-0.12.3+1/lib" />
+              <option value="$USER_HOME$/Development/flutter/packages/flutter_test/lib" />
             </list>
           </value>
         </entry>
-        <entry key="meta">
+        <entry key="matcher">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/meta-1.1.6/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/matcher-0.12.10/lib" />
             </list>
           </value>
         </entry>
-        <entry key="path">
+        <entry key="meta">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/path-1.6.2/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/meta-1.7.0/lib" />
             </list>
           </value>
         </entry>
-        <entry key="quiver">
+        <entry key="path">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/quiver-2.0.1/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/path-1.8.0/lib" />
             </list>
           </value>
         </entry>
         <entry key="sky_engine">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/bin/cache/pkg/sky_engine/lib" />
+              <option value="$USER_HOME$/Development/flutter/bin/cache/pkg/sky_engine/lib" />
             </list>
           </value>
         </entry>
         <entry key="source_span">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/source_span-1.4.1/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/source_span-1.8.1/lib" />
             </list>
           </value>
         </entry>
         <entry key="stack_trace">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/stack_trace-1.9.3/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/stack_trace-1.10.0/lib" />
             </list>
           </value>
         </entry>
         <entry key="stream_channel">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/stream_channel-1.6.8/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/stream_channel-2.1.0/lib" />
             </list>
           </value>
         </entry>
         <entry key="string_scanner">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/string_scanner-1.0.4/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/string_scanner-1.1.0/lib" />
             </list>
           </value>
         </entry>
         <entry key="term_glyph">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/term_glyph-1.0.1/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/term_glyph-1.2.0/lib" />
             </list>
           </value>
         </entry>
         <entry key="test_api">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/test_api-0.2.1/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/test_api-0.4.2/lib" />
             </list>
           </value>
         </entry>
         <entry key="typed_data">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/typed_data-1.1.6/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/typed_data-1.3.0/lib" />
             </list>
           </value>
         </entry>
         <entry key="vector_math">
           <value>
             <list>
-              <option value="$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/vector_math-2.0.8/lib" />
+              <option value="$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/vector_math-2.1.0/lib" />
             </list>
           </value>
         </entry>
       </option>
     </properties>
     <CLASSES>
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/async-2.0.8/lib" />
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/async_loader-0.1.2/lib" />
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/boolean_selector-1.0.4/lib" />
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/charcode-1.1.2/lib" />
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/collection-1.14.11/lib" />
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/cupertino_icons-0.1.2/lib" />
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/matcher-0.12.3+1/lib" />
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/meta-1.1.6/lib" />
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/path-1.6.2/lib" />
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/quiver-2.0.1/lib" />
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/source_span-1.4.1/lib" />
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/stack_trace-1.9.3/lib" />
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/stream_channel-1.6.8/lib" />
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/string_scanner-1.0.4/lib" />
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/term_glyph-1.0.1/lib" />
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/test_api-0.2.1/lib" />
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/typed_data-1.1.6/lib" />
-      <root url="file://$USER_HOME$/working/flutter/.pub-cache/hosted/pub.flutter-io.cn/vector_math-2.0.8/lib" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/pkg/sky_engine/lib" />
-      <root url="file://$USER_HOME$/working/flutter/packages/flutter/lib" />
-      <root url="file://$USER_HOME$/working/flutter/packages/flutter_test/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/async-2.8.1/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/async_loader-0.1.2/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/boolean_selector-2.1.0/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/characters-1.1.0/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/charcode-1.3.1/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/clock-1.1.0/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/collection-1.15.0/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/cupertino_icons-0.1.2/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/fake_async-1.2.0/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/matcher-0.12.10/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/meta-1.7.0/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/path-1.8.0/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/source_span-1.8.1/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/stack_trace-1.10.0/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/stream_channel-2.1.0/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/string_scanner-1.1.0/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/term_glyph-1.2.0/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/test_api-0.4.2/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/typed_data-1.3.0/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/.pub-cache/hosted/pub.flutter-io.cn/vector_math-2.1.0/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/pkg/sky_engine/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/packages/flutter/lib" />
+      <root url="file://$USER_HOME$/Development/flutter/packages/flutter_test/lib" />
     </CLASSES>
     <JAVADOC />
     <SOURCES />
diff --git a/.idea/libraries/Dart_SDK.xml b/.idea/libraries/Dart_SDK.xml
index 321b902..a54d004 100644
--- a/.idea/libraries/Dart_SDK.xml
+++ b/.idea/libraries/Dart_SDK.xml
@@ -1,25 +1,26 @@
 <component name="libraryTable">
   <library name="Dart SDK">
     <CLASSES>
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/async" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/cli" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/collection" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/convert" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/core" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/developer" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/html" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/indexed_db" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/io" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/isolate" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/js" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/js_util" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/math" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/mirrors" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/svg" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/typed_data" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/web_audio" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/web_gl" />
-      <root url="file://$USER_HOME$/working/flutter/bin/cache/dart-sdk/lib/web_sql" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/async" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/cli" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/collection" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/convert" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/core" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/developer" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/ffi" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/html" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/indexed_db" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/io" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/isolate" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/js" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/js_util" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/math" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/mirrors" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/svg" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/typed_data" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/web_audio" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/web_gl" />
+      <root url="file://$USER_HOME$/Development/flutter/bin/cache/dart-sdk/lib/web_sql" />
     </CLASSES>
     <JAVADOC />
     <SOURCES />
diff --git a/.idea/misc.xml b/.idea/misc.xml
index 3268472..0fe5195 100644
--- a/.idea/misc.xml
+++ b/.idea/misc.xml
@@ -1,5 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
+  <component name="FrameworkDetectionExcludesConfiguration">
+    <type id="android" />
+  </component>
   <component name="NullableNotNullManager">
     <option name="myDefaultNullable" value="android.support.annotation.Nullable" />
     <option name="myDefaultNotNull" value="android.support.annotation.NonNull" />
diff --git a/.idea/workspace.xml b/.idea/workspace.xml
index 4396722..d2d0c81 100644
--- a/.idea/workspace.xml
+++ b/.idea/workspace.xml
@@ -1,73 +1,39 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
+  <component name="AutoImportSettings">
+    <option name="autoReloadType" value="NONE" />
+  </component>
+  <component name="BranchesTreeState">
+    <expand>
+      <path>
+        <item name="ROOT" type="e8cecc67:BranchNodeDescriptor" />
+        <item name="LOCAL_ROOT" type="e8cecc67:BranchNodeDescriptor" />
+      </path>
+      <path>
+        <item name="ROOT" type="e8cecc67:BranchNodeDescriptor" />
+        <item name="REMOTE_ROOT" type="e8cecc67:BranchNodeDescriptor" />
+      </path>
+      <path>
+        <item name="ROOT" type="e8cecc67:BranchNodeDescriptor" />
+        <item name="REMOTE_ROOT" type="e8cecc67:BranchNodeDescriptor" />
+        <item name="GROUP_NODE:origin" type="e8cecc67:BranchNodeDescriptor" />
+      </path>
+    </expand>
+    <select />
+  </component>
   <component name="ChangeListManager">
-    <list default="true" id="04ebcdf9-5200-4936-8a61-c68499961c14" name="Default" comment="">
-      <change beforePath="$PROJECT_DIR$/.idea/libraries/Dart_Packages.xml" afterPath="$PROJECT_DIR$/.idea/libraries/Dart_Packages.xml" />
-      <change beforePath="$PROJECT_DIR$/.idea/libraries/Dart_SDK.xml" afterPath="$PROJECT_DIR$/.idea/libraries/Dart_SDK.xml" />
-      <change beforePath="$PROJECT_DIR$/.idea/workspace.xml" afterPath="$PROJECT_DIR$/.idea/workspace.xml" />
-      <change beforePath="$PROJECT_DIR$/example/pubspec.lock" afterPath="$PROJECT_DIR$/example/pubspec.lock" />
-      <change beforePath="$PROJECT_DIR$/flutter_dropdown_menu.iml" afterPath="$PROJECT_DIR$/flutter_dropdown_menu.iml" />
-      <change beforePath="$PROJECT_DIR$/lib/_src/dropdown_menu.dart" afterPath="$PROJECT_DIR$/lib/_src/dropdown_menu.dart" />
-      <change beforePath="$PROJECT_DIR$/pubspec.lock" afterPath="$PROJECT_DIR$/pubspec.lock" />
-      <change beforePath="$PROJECT_DIR$/test/dropdown_menu_test.dart" afterPath="$PROJECT_DIR$/test/dropdown_menu_test.dart" />
+    <list default="true" id="04ebcdf9-5200-4936-8a61-c68499961c14" name="Default" comment="Null safety migration">
+      <change beforePath="$PROJECT_DIR$/.idea/libraries/Dart_Packages.xml" beforeDir="false" afterPath="$PROJECT_DIR$/.idea/libraries/Dart_Packages.xml" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/.idea/workspace.xml" beforeDir="false" afterPath="$PROJECT_DIR$/.idea/workspace.xml" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/example/lib/main.dart" beforeDir="false" afterPath="$PROJECT_DIR$/example/lib/main.dart" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/example/pubspec.lock" beforeDir="false" afterPath="$PROJECT_DIR$/example/pubspec.lock" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/lib/_src/dropdown_menu.dart" beforeDir="false" afterPath="$PROJECT_DIR$/lib/_src/dropdown_menu.dart" afterDir="false" />
     </list>
-    <ignored path="$PROJECT_DIR$/.dart_tool/" />
-    <ignored path="$PROJECT_DIR$/.idea/" />
-    <ignored path="$PROJECT_DIR$/.pub/" />
-    <ignored path="$PROJECT_DIR$/build/" />
-    <option name="EXCLUDED_CONVERTED_TO_IGNORED" value="true" />
-    <option name="TRACKING_ENABLED" value="true" />
     <option name="SHOW_DIALOG" value="false" />
     <option name="HIGHLIGHT_CONFLICTS" value="true" />
     <option name="HIGHLIGHT_NON_ACTIVE_CHANGELIST" value="false" />
     <option name="LAST_RESOLUTION" value="IGNORE" />
   </component>
-  <component name="FileEditorManager">
-    <leaf SIDE_TABS_SIZE_LIMIT_KEY="300">
-      <file leaf-file-name="dropdown_menu.dart" pinned="false" current-in-tab="false">
-        <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_menu.dart">
-          <provider selected="true" editor-type-id="text-editor">
-            <state relative-caret-position="167">
-              <caret line="258" column="19" lean-forward="false" selection-start-line="258" selection-start-column="19" selection-end-line="258" selection-end-column="19" />
-              <folding>
-                <element signature="e#0#20#0" expanded="true" />
-              </folding>
-            </state>
-          </provider>
-        </entry>
-      </file>
-      <file leaf-file-name="dropdown_sliver.dart" pinned="false" current-in-tab="false">
-        <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_sliver.dart">
-          <provider selected="true" editor-type-id="text-editor">
-            <state relative-caret-position="0">
-              <caret line="0" column="0" lean-forward="false" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
-              <folding />
-            </state>
-          </provider>
-        </entry>
-      </file>
-      <file leaf-file-name="dropdown_templates.dart" pinned="false" current-in-tab="false">
-        <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_templates.dart">
-          <provider selected="true" editor-type-id="text-editor">
-            <state relative-caret-position="0">
-              <caret line="0" column="0" lean-forward="false" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
-              <folding />
-            </state>
-          </provider>
-        </entry>
-      </file>
-      <file leaf-file-name="dropdown_header.dart" pinned="false" current-in-tab="true">
-        <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_header.dart">
-          <provider selected="true" editor-type-id="text-editor">
-            <state relative-caret-position="109">
-              <caret line="152" column="30" lean-forward="true" selection-start-line="152" selection-start-column="30" selection-end-line="152" selection-end-column="30" />
-              <folding />
-            </state>
-          </provider>
-        </entry>
-      </file>
-    </leaf>
-  </component>
   <component name="FileTemplateManagerImpl">
     <option name="RECENT_TEMPLATES">
       <list>
@@ -75,133 +41,31 @@
       </list>
     </option>
   </component>
-  <component name="FindInProjectRecents">
-    <findStrings>
-      <find>_show</find>
-      <find>child</find>
-      <find>createState</find>
-      <find>turns</find>
-      <find>StatefulWidget</find>
-      <find>control</find>
-      <find>_TabControllerScope</find>
-      <find>onShow</find>
-      <find>DropdownMenuController</find>
-      <find>DefaultTabController</find>
-      <find>onHide</find>
-      <find>_DropdownMenuState</find>
-      <find>_onController</find>
-      <find>DropdownState</find>
-      <find>_DropdownHeaderState</find>
-      <find>activeIndex</find>
-      <find>createMenu</find>
-      <find>maxMenuHeight</find>
-      <find>getItemLabel</find>
-      <find>controller</find>
-      <find>_getHeight</find>
-      <find>shrinkWrap</find>
-      <find>_ensureHeight</find>
-      <find>itemExtent</find>
-      <find>SizedBox</find>
-      <find>height</find>
-      <find>getData</find>
-      <find>getSubData</find>
-      <find>color</find>
-      <find>blur</find>
-    </findStrings>
-    <replaceStrings>
-      <replace>_DropdownMenuScope</replace>
-      <replace>DropdownMenuController</replace>
-    </replaceStrings>
-  </component>
   <component name="Git.Settings">
     <option name="RECENT_GIT_ROOT_PATH" value="$PROJECT_DIR$" />
   </component>
-  <component name="GradleLocalSettings">
-    <option name="externalProjectsViewState">
-      <projects_view />
-    </option>
-  </component>
-  <component name="IdeDocumentHistory">
-    <option name="CHANGED_PATHS">
-      <list>
-        <option value="$PROJECT_DIR$/lib/flutter_dropdown_menu.dart" />
-        <option value="$PROJECT_DIR$/ROADMAP.md" />
-        <option value="$PROJECT_DIR$/example/lib/src/MeituanMenu.dart" />
-        <option value="$PROJECT_DIR$/example/lib/src/header_dropdown_menu.dart" />
-        <option value="$PROJECT_DIR$/example/lib/src/header_menu.dart" />
-        <option value="$PROJECT_DIR$/example/lib/src/menu_list.dart" />
-        <option value="$PROJECT_DIR$/lib/dropdown_templates.dart" />
-        <option value="$PROJECT_DIR$/lib/dropdown_sliver.dart" />
-        <option value="$PROJECT_DIR$/pubspec.yaml" />
-        <option value="$PROJECT_DIR$/CHANGELOG.md" />
-        <option value="$PROJECT_DIR$/example/pubspec.yaml" />
-        <option value="$PROJECT_DIR$/lib/dropdown_header.dart" />
-        <option value="$PROJECT_DIR$/lib/dropdown_list_menu.dart" />
-        <option value="$PROJECT_DIR$/lib/drapdown_common.dart" />
-        <option value="$PROJECT_DIR$/README.md" />
-        <option value="$PROJECT_DIR$/example/lib/main.dart" />
-        <option value="$PROJECT_DIR$/lib/dropdown_menu.dart" />
-        <option value="$PROJECT_DIR$/lib/_src/dropdown_menu.dart" />
-        <option value="$PROJECT_DIR$/test/dropdown_menu_test.dart" />
-      </list>
-    </option>
-  </component>
-  <component name="ProjectFrameBounds">
-    <option name="x" value="143" />
-    <option name="y" value="28" />
-    <option name="width" value="1400" />
-    <option name="height" value="877" />
-  </component>
+  <component name="ProjectId" id="1t0ykyz4EzxrvhfTl98Kamb8QZU" />
   <component name="ProjectLevelVcsManager" settingsEditedManually="true">
     <ConfirmationsSetting value="2" id="Add" />
   </component>
-  <component name="ProjectView">
-    <navigator currentView="ProjectPane" proportions="" version="1">
-      <flattenPackages />
-      <showMembers />
-      <showModules />
-      <showLibraryContents />
-      <hideEmptyPackages />
-      <abbreviatePackageNames />
-      <autoscrollToSource />
-      <autoscrollFromSource />
-      <sortByType />
-      <manualOrder />
-      <foldersAlwaysOnTop value="true" />
-    </navigator>
-    <panes>
-      <pane id="ProjectPane">
-        <subPane>
-          <expand>
-            <path>
-              <item name="flutter_dropdown_menu" type="b2602c69:ProjectViewProjectNode" />
-              <item name="flutter_dropdown_menu" type="462c0819:PsiDirectoryNode" />
-            </path>
-            <path>
-              <item name="flutter_dropdown_menu" type="b2602c69:ProjectViewProjectNode" />
-              <item name="flutter_dropdown_menu" type="462c0819:PsiDirectoryNode" />
-              <item name="lib" type="462c0819:PsiDirectoryNode" />
-            </path>
-          </expand>
-          <select />
-        </subPane>
-        <option name="show-excluded-files" value="false" />
-      </pane>
-      <pane id="AndroidView" />
-      <pane id="Scratches" />
-      <pane id="Scope" />
-      <pane id="PackagesPane" />
-    </panes>
+  <component name="ProjectViewState">
+    <option name="hideEmptyMiddlePackages" value="true" />
+    <option name="showLibraryContents" value="true" />
   </component>
   <component name="PropertiesComponent">
-    <property name="last_opened_file_path" value="$PROJECT_DIR$" />
+    <property name="RunOnceActivity.OpenProjectViewOnStart" value="true" />
+    <property name="RunOnceActivity.ShowReadmeOnStart" value="true" />
+    <property name="RunOnceActivity.cidr.known.project.marker" value="true" />
+    <property name="cidr.known.project.marker" value="true" />
     <property name="dart.analysis.tool.window.force.activate" value="false" />
-    <property name="show.migrate.to.gradle.popup" value="false" />
+    <property name="dart.analysis.tool.window.visible" value="false" />
     <property name="io.flutter.reload.alreadyRun" value="true" />
-    <property name="settings.editor.selected.configurable" value="flutter.settings" />
+    <property name="last_opened_file_path" value="$PROJECT_DIR$" />
     <property name="project.structure.last.edited" value="Modules" />
     <property name="project.structure.proportion" value="0.0" />
     <property name="project.structure.side.proportion" value="0.0" />
+    <property name="settings.editor.selected.configurable" value="org.jetbrains.plugins.github.ui.GithubSettingsConfigurable" />
+    <property name="show.migrate.to.gradle.popup" value="false" />
   </component>
   <component name="RecentsManager">
     <key name="MoveFile.RECENT_KEYS">
@@ -212,112 +76,47 @@
       <recent name="$PROJECT_DIR$/lib" />
     </key>
   </component>
-  <component name="RunDashboard">
-    <option name="ruleStates">
-      <list>
-        <RuleState>
-          <option name="name" value="ConfigurationTypeDashboardGroupingRule" />
-        </RuleState>
-        <RuleState>
-          <option name="name" value="StatusDashboardGroupingRule" />
-        </RuleState>
-      </list>
-    </option>
-  </component>
   <component name="RunManager">
-    <configuration default="true" type="AndroidJUnit" factoryName="Android JUnit">
-      <extension name="coverage" enabled="false" merge="false" sample_coverage="true" runner="idea" />
-      <module name="" />
-      <option name="ALTERNATIVE_JRE_PATH_ENABLED" value="false" />
-      <option name="ALTERNATIVE_JRE_PATH" />
-      <option name="PACKAGE_NAME" />
+    <configuration name="&lt;template&gt;" type="Applet" default="true" selected="false">
       <option name="MAIN_CLASS_NAME" />
-      <option name="METHOD_NAME" />
-      <option name="TEST_OBJECT" value="class" />
-      <option name="VM_PARAMETERS" value="-ea" />
-      <option name="PARAMETERS" />
-      <option name="WORKING_DIRECTORY" value="$MODULE_DIR$" />
-      <option name="ENV_VARIABLES" />
-      <option name="PASS_PARENT_ENVS" value="true" />
-      <option name="TEST_SEARCH_SCOPE">
-        <value defaultName="singleModule" />
-      </option>
-      <envs />
-      <patterns />
+      <option name="HTML_FILE_NAME" />
+      <option name="HTML_USED" value="false" />
+      <option name="WIDTH" value="400" />
+      <option name="HEIGHT" value="300" />
+      <option name="POLICY_FILE" value="$APPLICATION_HOME_DIR$/bin/appletviewer.policy" />
+      <option name="VM_PARAMETERS" />
+    </configuration>
+    <configuration name="&lt;template&gt;" type="#org.jetbrains.idea.devkit.run.PluginConfigurationType" default="true" selected="false">
+      <option name="VM_PARAMETERS" value="-Xmx512m -Xms256m -XX:MaxPermSize=250m -ea" />
     </configuration>
     <configuration default="true" type="Application" factoryName="Application">
-      <extension name="coverage" enabled="false" merge="false" sample_coverage="true" runner="idea" />
-      <option name="MAIN_CLASS_NAME" />
-      <option name="VM_PARAMETERS" />
-      <option name="PROGRAM_PARAMETERS" />
       <option name="WORKING_DIRECTORY" value="$PROJECT_DIR$" />
-      <option name="ALTERNATIVE_JRE_PATH_ENABLED" value="false" />
-      <option name="ALTERNATIVE_JRE_PATH" />
-      <option name="ENABLE_SWING_INSPECTOR" value="false" />
-      <option name="ENV_VARIABLES" />
-      <option name="PASS_PARENT_ENVS" value="true" />
-      <module name="" />
-      <envs />
+      <method v="2">
+        <option name="Make" enabled="true" />
+      </method>
     </configuration>
     <configuration name="main.dart" type="FlutterRunConfigurationType" factoryName="Flutter">
       <option name="filePath" value="$PROJECT_DIR$/example/lib/main.dart" />
+      <method v="2" />
     </configuration>
-    <configuration default="true" type="Remote" factoryName="Remote">
-      <option name="USE_SOCKET_TRANSPORT" value="true" />
-      <option name="SERVER_MODE" value="false" />
-      <option name="SHMEM_ADDRESS" value="javadebug" />
-      <option name="HOST" value="localhost" />
-      <option name="PORT" value="5005" />
+    <configuration default="true" type="JUnit" factoryName="JUnit">
+      <option name="TEST_OBJECT" value="class" />
+      <option name="WORKING_DIRECTORY" value="%MODULE_WORKING_DIR%" />
+      <method v="2">
+        <option name="Make" enabled="true" />
+      </method>
     </configuration>
-    <configuration default="true" type="TestNG" factoryName="TestNG">
-      <extension name="coverage" enabled="false" merge="false" sample_coverage="true" runner="idea" />
-      <module name="" />
-      <option name="ALTERNATIVE_JRE_PATH_ENABLED" value="false" />
-      <option name="ALTERNATIVE_JRE_PATH" />
-      <option name="SUITE_NAME" />
-      <option name="PACKAGE_NAME" />
-      <option name="MAIN_CLASS_NAME" />
-      <option name="METHOD_NAME" />
-      <option name="GROUP_NAME" />
+    <configuration default="true" type="TestNG">
       <option name="TEST_OBJECT" value="CLASS" />
-      <option name="VM_PARAMETERS" value="-ea" />
-      <option name="PARAMETERS" />
       <option name="WORKING_DIRECTORY" value="%MODULE_WORKING_DIR%" />
-      <option name="OUTPUT_DIRECTORY" />
-      <option name="ANNOTATION_TYPE" />
-      <option name="ENV_VARIABLES" />
-      <option name="PASS_PARENT_ENVS" value="true" />
-      <option name="TEST_SEARCH_SCOPE">
-        <value defaultName="singleModule" />
-      </option>
-      <option name="USE_DEFAULT_REPORTERS" value="false" />
-      <option name="PROPERTIES_FILE" />
-      <envs />
       <properties />
       <listeners />
-    </configuration>
-    <configuration name="&lt;template&gt;" type="Applet" default="true" selected="false">
-      <option name="MAIN_CLASS_NAME" />
-      <option name="HTML_FILE_NAME" />
-      <option name="HTML_USED" value="false" />
-      <option name="WIDTH" value="400" />
-      <option name="HEIGHT" value="300" />
-      <option name="POLICY_FILE" value="$APPLICATION_HOME_DIR$/bin/appletviewer.policy" />
-      <option name="VM_PARAMETERS" />
-    </configuration>
-    <configuration name="&lt;template&gt;" type="JUnit" default="true" selected="false">
-      <option name="MAIN_CLASS_NAME" />
-      <option name="VM_PARAMETERS" value="-ea" />
-      <option name="PARAMETERS" />
-      <option name="WORKING_DIRECTORY" value="%MODULE_WORKING_DIR%" />
-    </configuration>
-    <configuration name="&lt;template&gt;" type="#org.jetbrains.idea.devkit.run.PluginConfigurationType" default="true" selected="false">
-      <option name="VM_PARAMETERS" value="-Xmx512m -Xms256m -XX:MaxPermSize=250m -ea" />
+      <method v="2">
+        <option name="Make" enabled="true" />
+      </method>
     </configuration>
   </component>
-  <component name="ShelveChangesManager" show_recycled="false">
-    <option name="remove_strategy" value="false" />
-  </component>
+  <component name="SpellCheckerSettings" RuntimeDictionaries="0" Folders="0" CustomDictionaries="0" DefaultDictionary="application-level" UseSingleDictionary="true" transferred="true" />
   <component name="SvnConfiguration">
     <configuration />
   </component>
@@ -329,6 +128,28 @@
       <option name="presentableId" value="Default" />
       <updated>1527184261136</updated>
     </task>
+    <task id="LOCAL-00001" summary="修复适配 flutter 2.0">
+      <created>1621921150397</created>
+      <option name="number" value="00001" />
+      <option name="presentableId" value="LOCAL-00001" />
+      <option name="project" value="LOCAL" />
+      <updated>1621921150397</updated>
+    </task>
+    <task id="LOCAL-00002" summary="配置">
+      <created>1621921274268</created>
+      <option name="number" value="00002" />
+      <option name="presentableId" value="LOCAL-00002" />
+      <option name="project" value="LOCAL" />
+      <updated>1621921274268</updated>
+    </task>
+    <task id="LOCAL-00003" summary="Null safety migration">
+      <created>1637644863821</created>
+      <option name="number" value="00003" />
+      <option name="presentableId" value="LOCAL-00003" />
+      <option name="project" value="LOCAL" />
+      <updated>1637644863821</updated>
+    </task>
+    <option name="localTasksCounter" value="4" />
     <servers />
   </component>
   <component name="TodoView">
@@ -340,372 +161,33 @@
       <is-autoscroll-to-source value="true" />
     </todo-panel>
   </component>
-  <component name="ToolWindowManager">
-    <frame x="143" y="28" width="1400" height="877" extended-state="0" />
-    <editor active="true" />
-    <layout>
-      <window_info id="TODO" active="false" anchor="bottom" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.32833788" sideWeight="0.49427754" order="6" side_tool="false" content_ui="tabs" />
-      <window_info id="Messages" active="false" anchor="bottom" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.32736573" sideWeight="0.4867452" order="7" side_tool="false" content_ui="tabs" />
-      <window_info id="Palette&#9;" active="false" anchor="right" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.33" sideWeight="0.5" order="3" side_tool="false" content_ui="tabs" />
-      <window_info id="Image Layers" active="false" anchor="left" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.33" sideWeight="0.5" order="2" side_tool="false" content_ui="tabs" />
-      <window_info id="Capture Analysis" active="false" anchor="right" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.33" sideWeight="0.5" order="3" side_tool="false" content_ui="tabs" />
-      <window_info id="Event Log" active="false" anchor="bottom" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="true" show_stripe_button="true" weight="0.43222508" sideWeight="0.3969072" order="7" side_tool="true" content_ui="tabs" />
-      <window_info id="Dart Analysis" active="false" anchor="bottom" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.32833788" sideWeight="0.49427754" order="7" side_tool="false" content_ui="tabs" />
-      <window_info id="Run" active="false" anchor="bottom" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.32833788" sideWeight="0.49427754" order="2" side_tool="false" content_ui="tabs" />
-      <window_info id="Version Control" active="false" anchor="bottom" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.32833788" sideWeight="0.49427754" order="7" side_tool="false" content_ui="tabs" />
-      <window_info id="Terminal" active="false" anchor="bottom" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.32970026" sideWeight="0.49713877" order="7" side_tool="false" content_ui="tabs" />
-      <window_info id="Flutter Outline" active="false" anchor="right" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.33" sideWeight="0.5" order="3" side_tool="false" content_ui="tabs" />
-      <window_info id="Capture Tool" active="false" anchor="left" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.33" sideWeight="0.5" order="2" side_tool="false" content_ui="tabs" />
-      <window_info id="Designer" active="false" anchor="left" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.33" sideWeight="0.5" order="2" side_tool="false" content_ui="tabs" />
-      <window_info id="Project" active="false" anchor="left" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="true" show_stripe_button="true" weight="0.20692195" sideWeight="0.5" order="0" side_tool="false" content_ui="combo" />
-      <window_info id="Structure" active="false" anchor="left" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.25" sideWeight="0.5" order="1" side_tool="false" content_ui="tabs" />
-      <window_info id="Theme Preview" active="false" anchor="right" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.33" sideWeight="0.5" order="3" side_tool="false" content_ui="tabs" />
-      <window_info id="Debug" active="false" anchor="bottom" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="true" show_stripe_button="true" weight="0.43222508" sideWeight="0.6030928" order="3" side_tool="false" content_ui="tabs" />
-      <window_info id="Favorites" active="false" anchor="left" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.33" sideWeight="0.5" order="2" side_tool="true" content_ui="tabs" />
-      <window_info id="Flutter Inspector" active="false" anchor="right" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="true" show_stripe_button="true" weight="0.2857143" sideWeight="0.5" order="3" side_tool="false" content_ui="tabs" />
-      <window_info id="Cvs" active="false" anchor="bottom" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.25" sideWeight="0.5" order="4" side_tool="false" content_ui="tabs" />
-      <window_info id="Message" active="false" anchor="bottom" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.33" sideWeight="0.5" order="0" side_tool="false" content_ui="tabs" />
-      <window_info id="Commander" active="false" anchor="right" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.4" sideWeight="0.5" order="0" side_tool="false" content_ui="tabs" />
-      <window_info id="Hierarchy" active="false" anchor="right" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.25" sideWeight="0.5" order="2" side_tool="false" content_ui="combo" />
-      <window_info id="Ant Build" active="false" anchor="right" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.25" sideWeight="0.5" order="1" side_tool="false" content_ui="tabs" />
-      <window_info id="Inspection" active="false" anchor="bottom" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.4" sideWeight="0.5" order="5" side_tool="false" content_ui="tabs" />
-      <window_info id="Find" active="false" anchor="bottom" auto_hide="false" internal_type="DOCKED" type="DOCKED" visible="false" show_stripe_button="true" weight="0.33" sideWeight="0.5" order="1" side_tool="false" content_ui="tabs" />
-    </layout>
-  </component>
-  <component name="VcsContentAnnotationSettings">
-    <option name="myLimit" value="2678400000" />
+  <component name="Vcs.Log.Tabs.Properties">
+    <option name="TAB_STATES">
+      <map>
+        <entry key="MAIN">
+          <value>
+            <State />
+          </value>
+        </entry>
+      </map>
+    </option>
+    <option name="oldMeFiltersMigrated" value="true" />
   </component>
-  <component name="XDebuggerManager">
-    <breakpoint-manager>
-      <option name="time" value="64" />
-    </breakpoint-manager>
-    <watches-manager />
+  <component name="VcsManagerConfiguration">
+    <MESSAGE value="修复适配 flutter 2.0" />
+    <MESSAGE value="配置" />
+    <MESSAGE value="Null safety migration" />
+    <option name="LAST_COMMIT_MESSAGE" value="Null safety migration" />
   </component>
-  <component name="editorHistoryManager">
-    <entry file="file://$PROJECT_DIR$/example/pubspec.yaml">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="75">
-          <caret line="5" column="16" lean-forward="true" selection-start-line="5" selection-start-column="16" selection-end-line="5" selection-end-column="16" />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_list_menu.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="240">
-          <caret line="19" column="25" lean-forward="true" selection-start-line="19" selection-start-column="25" selection-end-line="19" selection-end-column="25" />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/README.md">
-      <provider selected="true" editor-type-id="split-provider[text-editor;markdown-preview-editor]">
-        <state split_layout="SPLIT">
-          <first_editor relative-caret-position="300">
-            <caret line="20" column="3" lean-forward="false" selection-start-line="20" selection-start-column="3" selection-end-line="20" selection-end-column="3" />
-          </first_editor>
-          <second_editor />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/pubspec.yaml">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="255">
-          <caret line="17" column="0" lean-forward="false" selection-start-line="17" selection-start-column="0" selection-end-line="17" selection-end-column="0" />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/dropdown_menu.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="30">
-          <caret line="2" column="25" lean-forward="false" selection-start-line="2" selection-start-column="25" selection-end-line="2" selection-end-column="25" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/ROADMAP.md">
-      <provider selected="true" editor-type-id="split-provider[text-editor;markdown-preview-editor]">
-        <state split_layout="SPLIT">
-          <first_editor relative-caret-position="90">
-            <caret line="6" column="16" lean-forward="true" selection-start-line="6" selection-start-column="16" selection-end-line="6" selection-end-column="16" />
-          </first_editor>
-          <second_editor />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/.gitignore">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="0">
-          <caret line="0" column="0" lean-forward="false" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/_src/drapdown_common.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="536">
-          <caret line="59" column="0" lean-forward="false" selection-start-line="59" selection-start-column="0" selection-end-line="59" selection-end-column="0" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_menu.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="30">
-          <caret line="2" column="47" lean-forward="false" selection-start-line="2" selection-start-column="47" selection-end-line="2" selection-end-column="47" />
-          <folding>
-            <element signature="e#0#20#0" expanded="true" />
-          </folding>
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_templates.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="180">
-          <caret line="12" column="25" lean-forward="false" selection-start-line="12" selection-start-column="25" selection-end-line="12" selection-end-column="25" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_header.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="135">
-          <caret line="14" column="6" lean-forward="true" selection-start-line="0" selection-start-column="0" selection-end-line="178" selection-end-column="0" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/pubspec.yaml">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="60">
-          <caret line="4" column="23" lean-forward="false" selection-start-line="4" selection-start-column="23" selection-end-line="4" selection-end-column="23" />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_sliver.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="0">
-          <caret line="0" column="0" lean-forward="false" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/../flutter/packages/flutter/lib/src/painting/edge_insets.dart" />
-    <entry file="file://$PROJECT_DIR$/../flutter/packages/flutter/lib/src/rendering/proxy_box.dart" />
-    <entry file="file://$PROJECT_DIR$/../flutter/packages/flutter/lib/src/widgets/scroll_view.dart" />
-    <entry file="file://$PROJECT_DIR$/../flutter/packages/flutter/lib/src/widgets/basic.dart" />
-    <entry file="file://$PROJECT_DIR$/../flutter/packages/flutter/lib/src/widgets/sliver.dart" />
-    <entry file="file://$PROJECT_DIR$/README.md">
-      <provider selected="true" editor-type-id="split-provider[text-editor;markdown-preview-editor]">
-        <state split_layout="SPLIT">
-          <first_editor relative-caret-position="98">
-            <caret line="16" column="13" lean-forward="true" selection-start-line="16" selection-start-column="13" selection-end-line="16" selection-end-column="13" />
-          </first_editor>
-          <second_editor />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/../flutter/bin/cache/pkg/sky_engine/lib/ui/painting.dart" />
-    <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_list_menu.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="135">
-          <caret line="48" column="11" lean-forward="true" selection-start-line="48" selection-start-column="11" selection-end-line="48" selection-end-column="11" />
-          <folding>
-            <element signature="e#0#39#0" expanded="false" />
-          </folding>
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_templates.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="180">
-          <caret line="12" column="25" lean-forward="false" selection-start-line="12" selection-start-column="25" selection-end-line="12" selection-end-column="25" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/example/lib/main.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="823">
-          <caret line="152" column="45" lean-forward="true" selection-start-line="152" selection-start-column="45" selection-end-line="152" selection-end-column="45" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_menu.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="128">
-          <caret line="152" column="60" lean-forward="false" selection-start-line="152" selection-start-column="60" selection-end-line="152" selection-end-column="60" />
-          <folding>
-            <element signature="e#0#20#0" expanded="true" />
-          </folding>
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_header.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="2545">
-          <caret line="179" column="0" lean-forward="false" selection-start-line="179" selection-start-column="0" selection-end-line="179" selection-end-column="0" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/_src/drapdown_common.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="131">
-          <caret line="78" column="30" lean-forward="false" selection-start-line="78" selection-start-column="30" selection-end-line="78" selection-end-column="30" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/dropdown_menu.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="90">
-          <caret line="6" column="35" lean-forward="true" selection-start-line="6" selection-start-column="35" selection-end-line="6" selection-end-column="35" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/_src/menu.dart" />
-    <entry file="file://$PROJECT_DIR$/lib/_src/controller.dart" />
-    <entry file="file://$PROJECT_DIR$/pubspec.yaml">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="60">
-          <caret line="4" column="23" lean-forward="false" selection-start-line="4" selection-start-column="23" selection-end-line="4" selection-end-column="23" />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/../flutter/packages/flutter/lib/src/painting/edge_insets.dart" />
-    <entry file="file://$PROJECT_DIR$/../flutter/packages/flutter/lib/src/rendering/proxy_box.dart" />
-    <entry file="file://$PROJECT_DIR$/../flutter/packages/flutter/lib/src/widgets/scroll_view.dart" />
-    <entry file="file://$PROJECT_DIR$/../flutter/packages/flutter/lib/src/widgets/basic.dart" />
-    <entry file="file://$PROJECT_DIR$/../flutter/packages/flutter/lib/src/widgets/sliver.dart" />
-    <entry file="file://$PROJECT_DIR$/README.md">
-      <provider selected="true" editor-type-id="split-provider[text-editor;markdown-preview-editor]">
-        <state split_layout="SPLIT">
-          <first_editor relative-caret-position="98">
-            <caret line="16" column="13" lean-forward="true" selection-start-line="16" selection-start-column="13" selection-end-line="16" selection-end-column="13" />
-          </first_editor>
-          <second_editor />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/../flutter/bin/cache/pkg/sky_engine/lib/ui/painting.dart" />
-    <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_list_menu.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="135">
-          <caret line="48" column="11" lean-forward="true" selection-start-line="48" selection-start-column="11" selection-end-line="48" selection-end-column="11" />
-          <folding>
-            <element signature="e#0#39#0" expanded="false" />
-          </folding>
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/dropdown_menu.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="90">
-          <caret line="6" column="35" lean-forward="false" selection-start-line="6" selection-start-column="35" selection-end-line="6" selection-end-column="35" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/example/lib/header_menu.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="0">
-          <caret line="0" column="0" lean-forward="false" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/example/lib/fix_menu.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="0">
-          <caret line="0" column="0" lean-forward="false" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
-          <folding>
-            <element signature="e#0#7671#0" expanded="false" />
-          </folding>
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/example/lib/config.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="0">
-          <caret line="0" column="0" lean-forward="false" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/example/lib/basic_menu.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="0">
-          <caret line="0" column="0" lean-forward="false" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/example/lib/main.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="-4036">
-          <caret line="17" column="47" lean-forward="false" selection-start-line="17" selection-start-column="47" selection-end-line="17" selection-end-column="47" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/test/dropdown_menu_test.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="0">
-          <caret line="0" column="0" lean-forward="true" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/_src/drapdown_common.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="56">
-          <caret line="72" column="34" lean-forward="true" selection-start-line="72" selection-start-column="34" selection-end-line="72" selection-end-column="34" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$USER_HOME$/working/flutter/packages/flutter/lib/src/scheduler/ticker.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="206">
-          <caret line="352" column="56" lean-forward="true" selection-start-line="352" selection-start-column="56" selection-end-line="352" selection-end-column="56" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_menu.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="167">
-          <caret line="258" column="19" lean-forward="false" selection-start-line="258" selection-start-column="19" selection-end-line="258" selection-end-column="19" />
-          <folding>
-            <element signature="e#0#20#0" expanded="true" />
-          </folding>
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_sliver.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="0">
-          <caret line="0" column="0" lean-forward="false" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_templates.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="0">
-          <caret line="0" column="0" lean-forward="false" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
-    <entry file="file://$PROJECT_DIR$/lib/_src/dropdown_header.dart">
-      <provider selected="true" editor-type-id="text-editor">
-        <state relative-caret-position="109">
-          <caret line="152" column="30" lean-forward="true" selection-start-line="152" selection-start-column="30" selection-end-line="152" selection-end-column="30" />
-          <folding />
-        </state>
-      </provider>
-    </entry>
+  <component name="WindowStateProjectService">
+    <state x="303" y="154" key="SettingsEditor" timestamp="1621921881167">
+      <screen x="0" y="25" width="1920" height="994" />
+    </state>
+    <state x="303" y="154" key="SettingsEditor/0.25.1920.994@0.25.1920.994" timestamp="1621921881167" />
+    <state x="560" y="259" key="Vcs.Push.Dialog.v2" timestamp="1621921606082">
+      <screen x="0" y="25" width="1920" height="994" />
+    </state>
+    <state x="560" y="259" key="Vcs.Push.Dialog.v2/0.25.1920.994@0.25.1920.994" timestamp="1621921606082" />
   </component>
   <component name="masterDetails">
     <states>
diff --git a/example/ios/Flutter/flutter_export_environment.sh b/example/ios/Flutter/flutter_export_environment.sh
new file mode 100755
index 0000000..26f0ba8
--- /dev/null
+++ b/example/ios/Flutter/flutter_export_environment.sh
@@ -0,0 +1,13 @@
+#!/bin/sh
+# This is a generated file; do not edit or check into version control.
+export "FLUTTER_ROOT=/Users/Ryan/Applications/flutter"
+export "FLUTTER_APPLICATION_PATH=/Users/Ryan/Projects/GymMaster/mrfussy/packages/dropdown_menu/example"
+export "COCOAPODS_PARALLEL_CODE_SIGN=true"
+export "FLUTTER_TARGET=lib/main.dart"
+export "FLUTTER_BUILD_DIR=build"
+export "FLUTTER_BUILD_NAME=1.0.0"
+export "FLUTTER_BUILD_NUMBER=1"
+export "DART_OBFUSCATION=false"
+export "TRACK_WIDGET_CREATION=true"
+export "TREE_SHAKE_ICONS=false"
+export "PACKAGE_CONFIG=.dart_tool/package_config.json"
diff --git a/example/lib/basic_menu.dart b/example/lib/basic_menu.dart
index 7d43c9e..f173658 100644
--- a/example/lib/basic_menu.dart
+++ b/example/lib/basic_menu.dart
@@ -1,20 +1,17 @@
-
 import 'package:flutter/material.dart';
 
-class BasicMenu extends StatefulWidget{
+class BasicMenu extends StatefulWidget {
+  const BasicMenu({super.key});
+
   @override
   State<StatefulWidget> createState() {
-    return new _BasicMenuState();
+    return _BasicMenuState();
   }
-
 }
 
-class _BasicMenuState extends State<BasicMenu>{
+class _BasicMenuState extends State<BasicMenu> {
   @override
   Widget build(BuildContext context) {
-    return new Container(
-
-    );
+    return Container();
   }
-
-}
\ No newline at end of file
+}
diff --git a/example/lib/config.dart b/example/lib/config.dart
index b0a8023..f661142 100644
--- a/example/lib/config.dart
+++ b/example/lib/config.dart
@@ -1,3 +1,4 @@
+// ignore_for_file: non_constant_identifier_names, constant_identifier_names
 
 import 'dart:convert';
 
@@ -71,5 +72,4 @@ String FOOD_JSON =
 
 List FOODS = json.decode(FOOD_JSON);
 
-
-const int FOOD_INDEX = 1;
\ No newline at end of file
+const int FOOD_INDEX = 1;
diff --git a/example/lib/fix_menu.dart b/example/lib/fix_menu.dart
index 3570913..b7c7447 100644
--- a/example/lib/fix_menu.dart
+++ b/example/lib/fix_menu.dart
@@ -186,23 +186,20 @@
 //  });
 //}
 
-
 import 'package:flutter/material.dart';
 
-class FixMenu extends StatefulWidget{
+class FixMenu extends StatefulWidget {
+  const FixMenu({super.key});
+
   @override
   State<StatefulWidget> createState() {
-    return new _FixMenuState();
+    return FixMenuState();
   }
-
 }
 
-class _FixMenuState extends State<FixMenu>{
+class FixMenuState extends State<FixMenu> {
   @override
   Widget build(BuildContext context) {
-    return new Container(
-
-    );
+    return Container();
   }
-
-}
\ No newline at end of file
+}
diff --git a/example/lib/header_menu.dart b/example/lib/header_menu.dart
index f67c4f3..2e8f441 100644
--- a/example/lib/header_menu.dart
+++ b/example/lib/header_menu.dart
@@ -1,20 +1,17 @@
-
 import 'package:flutter/material.dart';
 
-class HeaderMenu extends StatefulWidget{
+class HeaderMenu extends StatefulWidget {
+  const HeaderMenu({super.key});
+
   @override
   State<StatefulWidget> createState() {
-    return new _HeaderMenuState();
+    return HeaderMenuState();
   }
-
 }
 
-class _HeaderMenuState extends State<HeaderMenu>{
+class HeaderMenuState extends State<HeaderMenu> {
   @override
   Widget build(BuildContext context) {
-    return new Container(
-
-    );
+    return Container();
   }
-
-}
\ No newline at end of file
+}
diff --git a/example/lib/main.dart b/example/lib/main.dart
index 7a5f9c1..3aae1c2 100644
--- a/example/lib/main.dart
+++ b/example/lib/main.dart
@@ -1,33 +1,33 @@
-import 'dart:async';
+// ignore_for_file: non_constant_identifier_names, constant_identifier_names
 
-import 'package:flutter/material.dart';
+import 'package:flutter/material.dart' hide DropdownMenu;
 import 'package:dropdown_menu/dropdown_menu.dart';
-import 'dart:math' as math;
-import 'dart:io';
 import 'dart:convert';
 
-void main() => runApp(new MyApp());
+void main() => runApp(const MyApp());
 
 class MyApp extends StatelessWidget {
+  const MyApp({super.key});
+
   // This widget is the root of your application.
   @override
   Widget build(BuildContext context) {
-    return new MaterialApp(
+    return MaterialApp(
       title: 'Flutter Demo',
-      theme: new ThemeData(
+      theme: ThemeData(
           primarySwatch: Colors.blue, scaffoldBackgroundColor: Colors.white),
-      home: new MyHomePage(title: 'Flutter Demo Home Page'),
+      home: const MyHomePage(title: 'Flutter Demo Home Page'),
     );
   }
 }
 
 class MyHomePage extends StatefulWidget {
-  MyHomePage({Key key, this.title}) : super(key: key);
+  const MyHomePage({super.key, required this.title});
 
   final String title;
 
   @override
-  _MyHomePageState createState() => new _MyHomePageState();
+  MyHomePageState createState() => MyHomePageState();
 }
 
 const List<Map<String, dynamic>> ORDERS = [
@@ -102,40 +102,41 @@ List FOODS = json.decode(FOOD_JSON);
 
 const int FOOD_INDEX = 1;
 
-class _MyHomePageState extends State<MyHomePage> {
-  ScrollController scrollController;
+class MyHomePageState extends State<MyHomePage> {
+  late ScrollController scrollController;
   @override
   void initState() {
-    scrollController = new ScrollController();
-    globalKey = new GlobalKey();
+    scrollController = ScrollController();
+    globalKey = GlobalKey();
     super.initState();
   }
 
   DropdownMenu buildDropdownMenu() {
-    return new DropdownMenu(maxMenuHeight: kDropdownMenuItemHeight * 10,
+    return DropdownMenu(
+        maxMenuHeight: kDropdownMenuItemHeight * 10,
         //  activeIndex: activeIndex,
         menus: [
-          new DropdownMenuBuilder(
+          DropdownMenuBuilder(
               builder: (BuildContext context) {
-                return new DropdownListMenu(
+                return DropdownListMenu(
                   selectedIndex: TYPE_INDEX,
                   data: TYPES,
                   itemBuilder: buildCheckItem,
                 );
               },
               height: kDropdownMenuItemHeight * TYPES.length),
-          new DropdownMenuBuilder(
+          DropdownMenuBuilder(
               builder: (BuildContext context) {
-                return new DropdownListMenu(
+                return DropdownListMenu(
                   selectedIndex: ORDER_INDEX,
                   data: ORDERS,
                   itemBuilder: buildCheckItem,
                 );
               },
               height: kDropdownMenuItemHeight * ORDERS.length),
-          new DropdownMenuBuilder(
+          DropdownMenuBuilder(
               builder: (BuildContext context) {
-                return new DropdownTreeMenu(
+                return DropdownTreeMenu(
                   selectedIndex: 0,
                   subSelectedIndex: 0,
                   itemExtent: 45.0,
@@ -144,56 +145,57 @@ class _MyHomePageState extends State<MyHomePage> {
                   itemBuilder:
                       (BuildContext context, dynamic data, bool selected) {
                     if (!selected) {
-                      return new DecoratedBox(
-                          decoration: new BoxDecoration(
-                              border: new Border(
+                      return DecoratedBox(
+                          decoration: BoxDecoration(
+                              border: Border(
                                   right: Divider.createBorderSide(context))),
-                          child: new Padding(
+                          child: Padding(
                               padding: const EdgeInsets.only(left: 15.0),
-                              child: new Row(
+                              child: Row(
                                 children: <Widget>[
-                                  new Text(data['title']),
+                                  Text(data['title']),
                                 ],
                               )));
                     } else {
-                      return new DecoratedBox(
-                          decoration: new BoxDecoration(
-                              border: new Border(
+                      return DecoratedBox(
+                          decoration: BoxDecoration(
+                              border: Border(
                                   top: Divider.createBorderSide(context),
                                   bottom: Divider.createBorderSide(context))),
-                          child: new Container(
+                          child: Container(
                               color: Theme.of(context).scaffoldBackgroundColor,
-                              child: new Row(
+                              child: Row(
                                 children: <Widget>[
-                                  new Container(
+                                  Container(
                                       color: Theme.of(context).primaryColor,
                                       width: 3.0,
                                       height: 20.0),
-                                  new Padding(
-                                      padding: new EdgeInsets.only(left: 12.0),
-                                      child: new Text(data['title'])),
+                                  Padding(
+                                      padding:
+                                          const EdgeInsets.only(left: 12.0),
+                                      child: Text(data['title'])),
                                 ],
                               )));
                     }
                   },
                   subItemBuilder:
                       (BuildContext context, dynamic data, bool selected) {
-                    Color color = selected
+                    Color? color = selected
                         ? Theme.of(context).primaryColor
-                        : Theme.of(context).textTheme.body1.color;
+                        : Theme.of(context).textTheme.bodyLarge?.color;
 
-                    return new SizedBox(
+                    return SizedBox(
                       height: 45.0,
-                      child: new Row(
+                      child: Row(
                         children: <Widget>[
-                          new Text(
+                          Text(
                             data['title'],
-                            style: new TextStyle(color: color),
+                            style: TextStyle(color: color),
                           ),
-                          new Expanded(
-                              child: new Align(
+                          Expanded(
+                              child: Align(
                                   alignment: Alignment.centerRight,
-                                  child: new Text(data['count'].toString())))
+                                  child: Text(data['count'].toString())))
                         ],
                       ),
                     );
@@ -208,23 +210,23 @@ class _MyHomePageState extends State<MyHomePage> {
         ]);
   }
 
-  DropdownHeader buildDropdownHeader({DropdownMenuHeadTapCallback onTap}) {
-    return new DropdownHeader(
+  DropdownHeader buildDropdownHeader({DropdownMenuHeadTapCallback? onTap}) {
+    return DropdownHeader(
       onTap: onTap,
       titles: [TYPES[TYPE_INDEX], ORDERS[ORDER_INDEX], FOODS[0]['children'][0]],
     );
   }
 
   Widget buildFixHeaderDropdownMenu() {
-    return new DefaultDropdownMenuController(
-        child: new Column(
+    return DefaultDropdownMenuController(
+        child: Column(
       children: <Widget>[
         buildDropdownHeader(),
-        new Expanded(
-            child: new Stack(
+        Expanded(
+            child: Stack(
           children: <Widget>[
-            new ListView(
-              children: <Widget>[new Text("123123")],
+            ListView(
+              children: const <Widget>[Text("123123")],
             ),
             buildDropdownMenu()
           ],
@@ -234,73 +236,77 @@ class _MyHomePageState extends State<MyHomePage> {
   }
 
   Widget buildInnerListHeaderDropdownMenu() {
-    return new DefaultDropdownMenuController(
-        onSelected: ({int menuIndex, int index, int subIndex, dynamic data}) {
-          print(
+    return DefaultDropdownMenuController(
+        onSelected: (
+            {int? menuIndex, int? index, int? subIndex, dynamic data}) {
+          debugPrint(
               "menuIndex:$menuIndex index:$index subIndex:$subIndex data:$data");
         },
-        child: new Stack(
+        child: Stack(
           children: <Widget>[
-            new CustomScrollView(
-                controller: scrollController,
-                slivers: <Widget>[
-                  new SliverList(
-                      key: globalKey,
-                      delegate: new SliverChildBuilderDelegate(
-                          (BuildContext context, int index) {
-                        return new Container(
-                          color: Colors.black26,
-                          child: new Image.asset(
-                            "images/header.jpg",
-                            fit: BoxFit.fill,
-                          ),
-                        );
-                      }, childCount: 1)),
-                  new SliverPersistentHeader(
-                    delegate: new DropdownSliverChildBuilderDelegate(
-                        builder: (BuildContext context) {
-                      return new Container(
-                          color: Theme.of(context).scaffoldBackgroundColor,
-                          child: buildDropdownHeader(onTap: this._onTapHead));
-                    }),
-                    pinned: true,
-                    floating: true,
-                  ),
-                  new SliverList(
-                      delegate: new SliverChildBuilderDelegate(
-                          (BuildContext context, int index) {
-                    return new Container(
-                      color: Theme.of(context).scaffoldBackgroundColor,
-                      child: new Image.asset(
-                        "images/body.jpg",
+            CustomScrollView(controller: scrollController, slivers: <Widget>[
+              SliverList(
+                  key: globalKey,
+                  delegate: SliverChildBuilderDelegate(
+                      (BuildContext context, int index) {
+                    return Container(
+                      color: Colors.black26,
+                      child: Image.asset(
+                        "images/header.jpg",
                         fit: BoxFit.fill,
                       ),
                     );
-                  }, childCount: 10)),
-                ]),
-            new Padding(
-                padding: new EdgeInsets.only(top: 46.0),
+                  }, childCount: 1)),
+              SliverPersistentHeader(
+                delegate: DropdownSliverChildBuilderDelegate(
+                    builder: (BuildContext context) {
+                  return Container(
+                      color: Theme.of(context).scaffoldBackgroundColor,
+                      child: buildDropdownHeader(onTap: _onTapHead));
+                }),
+                pinned: true,
+                floating: true,
+              ),
+              SliverList(
+                  delegate: SliverChildBuilderDelegate(
+                      (BuildContext context, int index) {
+                return Container(
+                  color: Theme.of(context).scaffoldBackgroundColor,
+                  child: Image.asset(
+                    "images/body.jpg",
+                    fit: BoxFit.fill,
+                  ),
+                );
+              }, childCount: 10)),
+            ]),
+            Padding(
+                padding: const EdgeInsets.only(top: 46.0),
                 child: buildDropdownMenu())
           ],
         ));
   }
 
-  GlobalKey globalKey;
+  late GlobalKey globalKey;
+
   @override
   void dispose() {
     super.dispose();
   }
 
   void _onTapHead(int index) {
-    RenderObject renderObject = globalKey.currentContext.findRenderObject();
-    DropdownMenuController controller =
-        DefaultDropdownMenuController.of(globalKey.currentContext);
+    RenderObject? renderObject = globalKey.currentContext?.findRenderObject();
+    DropdownMenuController? controller = globalKey.currentContext == null
+        ? null
+        : DefaultDropdownMenuController.of(globalKey.currentContext!);
     //
     scrollController
-        .animateTo(scrollController.offset + renderObject.semanticBounds.height,
-            duration: new Duration(milliseconds: 150), curve: Curves.ease)
+        .animateTo(
+            scrollController.offset +
+                (renderObject?.semanticBounds.height ?? 0),
+            duration: const Duration(milliseconds: 150),
+            curve: Curves.ease)
         .whenComplete(() {
-      controller.show(index);
+      controller?.show(index);
     });
   }
 
@@ -308,14 +314,14 @@ class _MyHomePageState extends State<MyHomePage> {
 
   @override
   Widget build(BuildContext context) {
-    return new Scaffold(
-      appBar: new AppBar(
-        title: new Text(widget.title),
+    return Scaffold(
+      appBar: AppBar(
+        title: Text(widget.title),
       ),
       body: _currentIndex == 0
           ? buildFixHeaderDropdownMenu()
           : buildInnerListHeaderDropdownMenu(),
-      bottomNavigationBar: new BottomNavigationBar(
+      bottomNavigationBar: BottomNavigationBar(
           onTap: (int index) {
             setState(() {
               _currentIndex = index;
@@ -326,8 +332,8 @@ class _MyHomePageState extends State<MyHomePage> {
             {"name": "Fix", "icon": Icons.hearing},
             {"name": "ScrollView", "icon": Icons.list}
           ]
-              .map((dynamic data) => new BottomNavigationBarItem(
-                  title: new Text(data["name"]), icon: new Icon(data["icon"])))
+              .map((dynamic data) => BottomNavigationBarItem(
+                  label: data["name"], icon: Icon(data["icon"])))
               .toList()),
     );
   }
diff --git a/example/pubspec.lock b/example/pubspec.lock
index c20338f..e539fa3 100644
--- a/example/pubspec.lock
+++ b/example/pubspec.lock
@@ -1,55 +1,77 @@
 # Generated by pub
-# See https://www.dartlang.org/tools/pub/glossary#lockfile
+# See https://dart.dev/tools/pub/glossary#lockfile
 packages:
   async:
     dependency: transitive
     description:
       name: async
-      url: "https://pub.flutter-io.cn"
+      sha256: bfe67ef28df125b7dddcea62755991f807aa39a2492a23e1550161692950bbe0
+      url: "https://pub.dev"
     source: hosted
-    version: "2.0.8"
+    version: "2.10.0"
   async_loader:
     dependency: "direct main"
     description:
       name: async_loader
-      url: "https://pub.flutter-io.cn"
+      sha256: f36721389a85237927f93fd09ec9e0eb23da1e47502d380e67ecd0a731def5b0
+      url: "https://pub.dev"
     source: hosted
     version: "0.1.2"
   boolean_selector:
     dependency: transitive
     description:
       name: boolean_selector
-      url: "https://pub.flutter-io.cn"
+      sha256: "6cfb5af12253eaf2b368f07bacc5a80d1301a071c73360d746b7f2e32d762c66"
+      url: "https://pub.dev"
     source: hosted
-    version: "1.0.4"
-  charcode:
+    version: "2.1.1"
+  characters:
     dependency: transitive
     description:
-      name: charcode
-      url: "https://pub.flutter-io.cn"
+      name: characters
+      sha256: e6a326c8af69605aec75ed6c187d06b349707a27fbff8222ca9cc2cff167975c
+      url: "https://pub.dev"
     source: hosted
-    version: "1.1.2"
+    version: "1.2.1"
+  clock:
+    dependency: transitive
+    description:
+      name: clock
+      sha256: cb6d7f03e1de671e34607e909a7213e31d7752be4fb66a86d29fe1eb14bfb5cf
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.1.1"
   collection:
     dependency: transitive
     description:
       name: collection
-      url: "https://pub.flutter-io.cn"
+      sha256: cfc915e6923fe5ce6e153b0723c753045de46de1b4d63771530504004a45fae0
+      url: "https://pub.dev"
     source: hosted
-    version: "1.14.11"
+    version: "1.17.0"
   cupertino_icons:
     dependency: "direct main"
     description:
       name: cupertino_icons
-      url: "https://pub.flutter-io.cn"
+      sha256: a937da4c006989739ceb4d10e3bd6cce64ca85d0fe287fc5b2b9f6ee757dcee6
+      url: "https://pub.dev"
     source: hosted
-    version: "0.1.2"
+    version: "0.1.3"
   dropdown_menu:
     dependency: "direct main"
     description:
       path: ".."
       relative: true
     source: path
-    version: "1.1.0"
+    version: "1.1.1"
+  fake_async:
+    dependency: transitive
+    description:
+      name: fake_async
+      sha256: "511392330127add0b769b75a987850d136345d9227c6b94c96a04cf4a391bf78"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.3.1"
   flutter:
     dependency: "direct main"
     description: flutter
@@ -60,34 +82,46 @@ packages:
     description: flutter
     source: sdk
     version: "0.0.0"
+  js:
+    dependency: transitive
+    description:
+      name: js
+      sha256: "5528c2f391ededb7775ec1daa69e65a2d61276f7552de2b5f7b8d34ee9fd4ab7"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.6.5"
   matcher:
     dependency: transitive
     description:
       name: matcher
-      url: "https://pub.flutter-io.cn"
+      sha256: "16db949ceee371e9b99d22f88fa3a73c4e59fd0afed0bd25fc336eb76c198b72"
+      url: "https://pub.dev"
     source: hosted
-    version: "0.12.3+1"
+    version: "0.12.13"
+  material_color_utilities:
+    dependency: transitive
+    description:
+      name: material_color_utilities
+      sha256: d92141dc6fe1dad30722f9aa826c7fbc896d021d792f80678280601aff8cf724
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.2.0"
   meta:
     dependency: transitive
     description:
       name: meta
-      url: "https://pub.flutter-io.cn"
+      sha256: "6c268b42ed578a53088d834796959e4a1814b5e9e164f147f580a386e5decf42"
+      url: "https://pub.dev"
     source: hosted
-    version: "1.1.6"
+    version: "1.8.0"
   path:
     dependency: transitive
     description:
       name: path
-      url: "https://pub.flutter-io.cn"
+      sha256: db9d4f58c908a4ba5953fcee2ae317c94889433e5024c27ce74a37f94267945b
+      url: "https://pub.dev"
     source: hosted
-    version: "1.6.2"
-  quiver:
-    dependency: transitive
-    description:
-      name: quiver
-      url: "https://pub.flutter-io.cn"
-    source: hosted
-    version: "2.0.1"
+    version: "1.8.2"
   sky_engine:
     dependency: transitive
     description: flutter
@@ -97,58 +131,58 @@ packages:
     dependency: transitive
     description:
       name: source_span
-      url: "https://pub.flutter-io.cn"
+      sha256: dd904f795d4b4f3b870833847c461801f6750a9fa8e61ea5ac53f9422b31f250
+      url: "https://pub.dev"
     source: hosted
-    version: "1.4.1"
+    version: "1.9.1"
   stack_trace:
     dependency: transitive
     description:
       name: stack_trace
-      url: "https://pub.flutter-io.cn"
+      sha256: c3c7d8edb15bee7f0f74debd4b9c5f3c2ea86766fe4178eb2a18eb30a0bdaed5
+      url: "https://pub.dev"
     source: hosted
-    version: "1.9.3"
+    version: "1.11.0"
   stream_channel:
     dependency: transitive
     description:
       name: stream_channel
-      url: "https://pub.flutter-io.cn"
+      sha256: "83615bee9045c1d322bbbd1ba209b7a749c2cbcdcb3fdd1df8eb488b3279c1c8"
+      url: "https://pub.dev"
     source: hosted
-    version: "1.6.8"
+    version: "2.1.1"
   string_scanner:
     dependency: transitive
     description:
       name: string_scanner
-      url: "https://pub.flutter-io.cn"
+      sha256: "556692adab6cfa87322a115640c11f13cb77b3f076ddcc5d6ae3c20242bedcde"
+      url: "https://pub.dev"
     source: hosted
-    version: "1.0.4"
+    version: "1.2.0"
   term_glyph:
     dependency: transitive
     description:
       name: term_glyph
-      url: "https://pub.flutter-io.cn"
+      sha256: a29248a84fbb7c79282b40b8c72a1209db169a2e0542bce341da992fe1bc7e84
+      url: "https://pub.dev"
     source: hosted
-    version: "1.0.1"
+    version: "1.2.1"
   test_api:
     dependency: transitive
     description:
       name: test_api
-      url: "https://pub.flutter-io.cn"
-    source: hosted
-    version: "0.2.1"
-  typed_data:
-    dependency: transitive
-    description:
-      name: typed_data
-      url: "https://pub.flutter-io.cn"
+      sha256: ad540f65f92caa91bf21dfc8ffb8c589d6e4dc0c2267818b4cc2792857706206
+      url: "https://pub.dev"
     source: hosted
-    version: "1.1.6"
+    version: "0.4.16"
   vector_math:
     dependency: transitive
     description:
       name: vector_math
-      url: "https://pub.flutter-io.cn"
+      sha256: "80b3257d1492ce4d091729e3a67a60407d227c27241d6927be0130c98e741803"
+      url: "https://pub.dev"
     source: hosted
-    version: "2.0.8"
+    version: "2.1.4"
 sdks:
-  dart: ">=2.0.0 <3.0.0"
-  flutter: ">=0.1.4 <3.0.0"
+  dart: ">=2.18.0 <3.0.0"
+  flutter: ">=0.1.4"
diff --git a/example/pubspec.yaml b/example/pubspec.yaml
index d777eba..f3a032a 100644
--- a/example/pubspec.yaml
+++ b/example/pubspec.yaml
@@ -1,6 +1,9 @@
 name: example
 description: A new Flutter project.
 
+environment:
+  sdk: '>=2.17.0 <3.0.0'
+
 dependencies:
   flutter:
     sdk: flutter
diff --git a/flutter_dropdown_menu.iml b/flutter_dropdown_menu.iml
index b06c613..9b91862 100644
--- a/flutter_dropdown_menu.iml
+++ b/flutter_dropdown_menu.iml
@@ -1,10 +1,18 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <module type="JAVA_MODULE" version="4">
+  <component name="FacetManager">
+    <facet type="android" name="Android">
+      <configuration>
+        <option name="ALLOW_USER_CONFIGURATION" value="false" />
+      </configuration>
+    </facet>
+  </component>
   <component name="NewModuleRootManager" inherit-compiler-output="true">
     <exclude-output />
     <content url="file://$MODULE_DIR$">
       <sourceFolder url="file://$MODULE_DIR$/lib" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/test" isTestSource="true" />
+      <sourceFolder url="file://$MODULE_DIR$/gen" isTestSource="false" generated="true" />
       <excludeFolder url="file://$MODULE_DIR$/.dart_tool" />
       <excludeFolder url="file://$MODULE_DIR$/.idea" />
       <excludeFolder url="file://$MODULE_DIR$/.pub" />
diff --git a/lib/_src/drapdown_common.dart b/lib/_src/drapdown_common.dart
index 07b6b8b..e8042ad 100644
--- a/lib/_src/drapdown_common.dart
+++ b/lib/_src/drapdown_common.dart
@@ -1,4 +1,5 @@
-import 'package:flutter/foundation.dart';
+// ignore_for_file: constant_identifier_names
+
 import 'package:flutter/widgets.dart';
 
 enum DropdownEvent {
@@ -14,19 +15,19 @@ enum DropdownEvent {
 
 class DropdownMenuController extends ChangeNotifier {
   //user interaction event name
-  DropdownEvent event;
+  DropdownEvent? event;
 
   // whitch menu index
-  int menuIndex;
+  int? menuIndex;
 
   /// selected data
   dynamic data;
 
   /// item index in list [TreeMenuList] or [MenuList] or your custom menu
-  int index;
+  int? index;
 
   /// item index in sublist of [TreeMenuList]
-  int subIndex;
+  int? subIndex;
 
   void hide() {
     event = DropdownEvent.HIDE;
@@ -39,7 +40,7 @@ class DropdownMenuController extends ChangeNotifier {
     notifyListeners();
   }
 
-  void select(dynamic data, {int index, int subIndex}) {
+  void select(dynamic data, {int? index, int? subIndex}) {
     event = DropdownEvent.SELECT;
     this.data = data;
     this.index = index;
@@ -48,73 +49,76 @@ class DropdownMenuController extends ChangeNotifier {
   }
 }
 
-typedef DropdownMenuOnSelected(
-    {int menuIndex, int index, int subIndex, dynamic data});
+typedef DropdownMenuOnSelected = Function(
+    {int? menuIndex, int? index, int? subIndex, dynamic data});
 
 class DefaultDropdownMenuController extends StatefulWidget {
   const DefaultDropdownMenuController({
-    Key key,
-    @required this.child,
+    Key? key,
+    required this.child,
     this.onSelected,
   }) : super(key: key);
 
   final Widget child;
 
-  final DropdownMenuOnSelected onSelected;
+  final DropdownMenuOnSelected? onSelected;
 
-  static DropdownMenuController of(BuildContext context) {
-    final _DropdownMenuControllerScope scope =
-        context.inheritFromWidgetOfExactType(_DropdownMenuControllerScope);
+  static DropdownMenuController? of(BuildContext context) {
+    final _DropdownMenuControllerScope? scope =
+        context.dependOnInheritedWidgetOfExactType(
+            aspect: _DropdownMenuControllerScope);
     return scope?.controller;
   }
 
   @override
-  _DefaultDropdownMenuControllerState createState() =>
-      new _DefaultDropdownMenuControllerState();
+  DefaultDropdownMenuControllerState createState() =>
+      DefaultDropdownMenuControllerState();
 }
 
-class _DefaultDropdownMenuControllerState
+class DefaultDropdownMenuControllerState
     extends State<DefaultDropdownMenuController>
     with SingleTickerProviderStateMixin {
-  DropdownMenuController _controller;
+  DropdownMenuController? _controller;
 
   @override
   void initState() {
     super.initState();
-    _controller = new DropdownMenuController();
-    _controller.addListener(_onController);
+    _controller = DropdownMenuController();
+    _controller!.addListener(_onController);
   }
 
   void _onController() {
-    switch (_controller.event) {
+    switch (_controller!.event) {
       case DropdownEvent.SELECT:
         {
           //通知widget
           if (widget.onSelected == null) return;
-          widget.onSelected(
-              data: _controller.data,
-              menuIndex: _controller.menuIndex,
-              index: _controller.index,
-              subIndex: _controller.subIndex);
+          widget.onSelected!(
+              data: _controller!.data,
+              menuIndex: _controller!.menuIndex,
+              index: _controller!.index,
+              subIndex: _controller!.subIndex);
         }
         break;
       case DropdownEvent.ACTIVE:
         break;
       case DropdownEvent.HIDE:
         break;
+      default:
+        break;
     }
   }
 
   @override
   void dispose() {
-    _controller.removeListener(_onController);
-    _controller.dispose();
+    _controller!.removeListener(_onController);
+    _controller!.dispose();
     super.dispose();
   }
 
   @override
   Widget build(BuildContext context) {
-    return new _DropdownMenuControllerScope(
+    return _DropdownMenuControllerScope(
       controller: _controller,
       enabled: TickerMode.of(context),
       child: widget.child,
@@ -124,11 +128,11 @@ class _DefaultDropdownMenuControllerState
 
 class _DropdownMenuControllerScope extends InheritedWidget {
   const _DropdownMenuControllerScope(
-      {Key key, this.controller, this.enabled, Widget child})
+      {Key? key, this.controller, this.enabled, required Widget child})
       : super(key: key, child: child);
 
-  final DropdownMenuController controller;
-  final bool enabled;
+  final DropdownMenuController? controller;
+  final bool? enabled;
 
   @override
   bool updateShouldNotify(_DropdownMenuControllerScope old) {
@@ -137,21 +141,21 @@ class _DropdownMenuControllerScope extends InheritedWidget {
 }
 
 abstract class DropdownWidget extends StatefulWidget {
-  final DropdownMenuController controller;
+  final DropdownMenuController? controller;
 
-  DropdownWidget({Key key, this.controller}) : super(key: key);
+  const DropdownWidget({Key? key, this.controller}) : super(key: key);
 
   @override
   DropdownState<DropdownWidget> createState();
 }
 
 abstract class DropdownState<T extends DropdownWidget> extends State<T> {
-  DropdownMenuController controller;
+  DropdownMenuController? controller;
 
   @override
   void dispose() {
     if (controller != null) {
-      controller.removeListener(_onController);
+      controller!.removeListener(_onController);
     }
     super.dispose();
   }
@@ -166,7 +170,7 @@ abstract class DropdownState<T extends DropdownWidget> extends State<T> {
       }
 
       if (controller != null) {
-        controller.addListener(_onController);
+        controller!.addListener(_onController);
       }
     }
     super.didChangeDependencies();
@@ -176,27 +180,26 @@ abstract class DropdownState<T extends DropdownWidget> extends State<T> {
   void didUpdateWidget(T oldWidget) {
     if (widget.controller != null) {
       if (controller != null) {
-        controller.removeListener(_onController);
+        controller!.removeListener(_onController);
       }
       controller = widget.controller;
-      controller.addListener(_onController);
+      controller!.addListener(_onController);
     }
 
     super.didUpdateWidget(oldWidget);
   }
 
   void _onController() {
-    onEvent(controller.event);
+    onEvent(controller!.event);
   }
 
-  void onEvent(DropdownEvent event);
+  void onEvent(DropdownEvent? event);
 }
 
 class DropdownMenuBuilder {
   final WidgetBuilder builder;
-  final double height;
+  final double? height;
 
   //if height == null , use [DropdownMenu.maxMenuHeight]
-  DropdownMenuBuilder({@required this.builder, this.height})
-      : assert(builder != null);
+  DropdownMenuBuilder({required this.builder, this.height});
 }
diff --git a/lib/_src/dropdown_header.dart b/lib/_src/dropdown_header.dart
index df32407..d51c34b 100644
--- a/lib/_src/dropdown_header.dart
+++ b/lib/_src/dropdown_header.dart
@@ -1,91 +1,105 @@
-import 'package:flutter/widgets.dart';
-import 'package:flutter/foundation.dart';
-
 import 'package:flutter/material.dart';
 
 import 'package:dropdown_menu/_src/drapdown_common.dart';
 
-typedef void DropdownMenuHeadTapCallback(int index);
+typedef DropdownMenuHeadTapCallback = void Function(int index);
 
-typedef String GetItemLabel(dynamic data);
+typedef GetItemLabel<T> = String? Function(T data);
 
-String defaultGetItemLabel(dynamic data) {
+String? defaultGetItemLabel<T>(T data) {
   if (data is String) return data;
-  return data["title"];
+  return (data as Map)["title"];
 }
 
-class DropdownHeader extends DropdownWidget {
-  final List<dynamic> titles;
-  final int activeIndex;
-  final DropdownMenuHeadTapCallback onTap;
+class DropdownHeader<T> extends DropdownWidget {
+  final List<T> titles;
+  final int? activeIndex;
+  final DropdownMenuHeadTapCallback? onTap;
+  final int maxLines;
+
+  final TextOverflow overflow;
+
+  final bool showLeftLine;
 
   /// height of menu
   final double height;
 
   /// get label callback
-  final GetItemLabel getItemLabel;
+  final GetItemLabel<T> getItemLabel;
 
   DropdownHeader(
-      {@required this.titles,
+      {super.key,
+      super.controller,
+      required this.titles,
       this.activeIndex,
-      DropdownMenuController controller,
       this.onTap,
-      Key key,
-      this.height: 46.0,
-      GetItemLabel getItemLabel})
+      this.height = 46.0,
+      this.maxLines = 1,
+      this.overflow = TextOverflow.ellipsis,
+      this.showLeftLine = true,
+      GetItemLabel? getItemLabel})
       : getItemLabel = getItemLabel ?? defaultGetItemLabel,
-        assert(titles != null && titles.length > 0),
-        super(key: key, controller: controller);
+        assert(titles.isNotEmpty);
 
   @override
   DropdownState<DropdownWidget> createState() {
-    return new _DropdownHeaderState();
+    return _DropdownHeaderState();
   }
 }
 
-class _DropdownHeaderState extends DropdownState<DropdownHeader> {
-  Widget buildItem(
-      BuildContext context, dynamic title, bool selected, int index) {
+class _DropdownHeaderState<T> extends DropdownState<DropdownHeader<T>> {
+  Widget buildItem(BuildContext context, T title, bool selected, int index) {
     final Color primaryColor = Theme.of(context).primaryColor;
     final Color unselectedColor = Theme.of(context).unselectedWidgetColor;
-    final GetItemLabel getItemLabel = widget.getItemLabel;
+    final GetItemLabel<T> getItemLabel = widget.getItemLabel;
 
-    return new GestureDetector(
+    return GestureDetector(
       behavior: HitTestBehavior.opaque,
-      child: new Padding(
-          padding: new EdgeInsets.fromLTRB(0.0, 10.0, 0.0, 10.0),
-          child: new DecoratedBox(
-              decoration: new BoxDecoration(
-                  border: new Border(left: Divider.createBorderSide(context))),
-              child: new Center(
-                  child: new Row(
-                      mainAxisSize: MainAxisSize.min,
-                      children: <Widget>[
-                    new Text(
-                      getItemLabel(title),
-                      style: new TextStyle(
-                        color: selected ? primaryColor : unselectedColor,
-                      ),
-                    ),
-                    new Icon(
-                      selected ? Icons.arrow_drop_up : Icons.arrow_drop_down,
+      child: Padding(
+        padding: const EdgeInsets.fromLTRB(0.0, 10.0, 0.0, 10.0),
+        child: DecoratedBox(
+          decoration: BoxDecoration(
+              border: Border(
+                  left: widget.showLeftLine
+                      ? Divider.createBorderSide(context)
+                      : BorderSide.none)),
+          child: Center(
+            child: Row(
+              mainAxisSize: MainAxisSize.min,
+              children: <Widget>[
+                Flexible(
+                  child: Text(
+                    getItemLabel(title)!,
+                    style: TextStyle(
                       color: selected ? primaryColor : unselectedColor,
-                    )
-                  ])))),
+                    ),
+                    maxLines: widget.maxLines,
+                    overflow: widget.overflow,
+                  ),
+                ),
+                Icon(
+                  selected ? Icons.arrow_drop_up : Icons.arrow_drop_down,
+                  color: selected ? primaryColor : unselectedColor,
+                ),
+              ],
+            ),
+          ),
+        ),
+      ),
       onTap: () {
         if (widget.onTap != null) {
-          widget.onTap(index);
+          widget.onTap!(index);
 
           return;
         }
         if (controller != null) {
           if (_activeIndex == index) {
-            controller.hide();
+            controller!.hide();
             setState(() {
               _activeIndex = null;
             });
           } else {
-            controller.show(index);
+            controller!.show(index);
           }
         }
         //widget.onTap(index);
@@ -93,15 +107,15 @@ class _DropdownHeaderState extends DropdownState<DropdownHeader> {
     );
   }
 
-  int _activeIndex;
-  List<dynamic> _titles;
+  int? _activeIndex;
+  late List<T> _titles;
 
   @override
   Widget build(BuildContext context) {
     List<Widget> list = [];
 
-    final int activeIndex = _activeIndex;
-    final List<dynamic> titles = _titles;
+    final int? activeIndex = _activeIndex;
+    final List<T> titles = _titles;
     final double height = widget.height;
 
     for (int i = 0, c = widget.titles.length; i < c; ++i) {
@@ -109,24 +123,24 @@ class _DropdownHeaderState extends DropdownState<DropdownHeader> {
     }
 
     list = list.map((Widget widget) {
-      return new Expanded(
+      return Expanded(
         child: widget,
       );
     }).toList();
 
-    final Decoration decoration = new BoxDecoration(
-      border: new Border(
+    final Decoration decoration = BoxDecoration(
+      border: Border(
         bottom: Divider.createBorderSide(context),
       ),
     );
 
-    return new DecoratedBox(
+    return DecoratedBox(
       decoration: decoration,
-      child: new SizedBox(
-          child: new Row(
+      child: SizedBox(
+          height: height,
+          child: Row(
             children: list,
-          ),
-          height: height),
+          )),
     );
   }
 
@@ -137,7 +151,7 @@ class _DropdownHeaderState extends DropdownState<DropdownHeader> {
   }
 
   @override
-  void onEvent(DropdownEvent event) {
+  void onEvent(DropdownEvent? event) {
     switch (event) {
       case DropdownEvent.SELECT:
         {
@@ -145,8 +159,8 @@ class _DropdownHeaderState extends DropdownState<DropdownHeader> {
 
           setState(() {
             _activeIndex = null;
-            String label = widget.getItemLabel(controller.data);
-            _titles[controller.menuIndex] = label;
+            dynamic title = controller!.data;
+            _titles[controller!.menuIndex!] = title as T;
           });
         }
         break;
@@ -160,12 +174,14 @@ class _DropdownHeaderState extends DropdownState<DropdownHeader> {
         break;
       case DropdownEvent.ACTIVE:
         {
-          if (_activeIndex == controller.menuIndex) return;
+          if (_activeIndex == controller!.menuIndex) return;
           setState(() {
-            _activeIndex = controller.menuIndex;
+            _activeIndex = controller!.menuIndex;
           });
         }
         break;
+      default:
+        break;
     }
   }
 }
diff --git a/lib/_src/dropdown_list_menu.dart b/lib/_src/dropdown_list_menu.dart
index d207938..6dfb735 100644
--- a/lib/_src/dropdown_list_menu.dart
+++ b/lib/_src/dropdown_list_menu.dart
@@ -3,32 +3,34 @@ import 'package:flutter/widgets.dart';
 
 import 'package:dropdown_menu/_src/drapdown_common.dart';
 
-typedef Widget MenuItemBuilder<T>(BuildContext context, T data, bool selected);
-typedef void MenuItemOnTap<T>(T data, int index);
-typedef List<E> GetSubData<T, E>(T data);
+typedef MenuItemBuilder<T> = Widget Function(
+    BuildContext context, T? data, bool selected);
+typedef MenuItemOnTap<T> = void Function(T data, int index);
+typedef GetSubData<T, E> = List<E> Function(T data);
 
 const double kDropdownMenuItemHeight = 45.0;
 
 class DropdownListMenu<T> extends DropdownWidget {
-  final List<T> data;
-  final int selectedIndex;
-  final MenuItemBuilder itemBuilder;
+  final List<T>? data;
+  final int? selectedIndex;
+  final MenuItemBuilder<T>? itemBuilder;
   final double itemExtent;
 
   DropdownListMenu(
-      {this.data,
+      {super.key,
+      this.data,
       this.selectedIndex,
       this.itemBuilder,
-      this.itemExtent: kDropdownMenuItemHeight});
+      this.itemExtent = kDropdownMenuItemHeight});
 
   @override
   DropdownState<DropdownWidget> createState() {
-    return new _MenuListState<T>();
+    return MenuListState<T>();
   }
 }
 
-class _MenuListState<T> extends DropdownState<DropdownListMenu<T>> {
-  int _selectedIndex;
+class MenuListState<T> extends DropdownState<DropdownListMenu<T>> {
+  int? _selectedIndex;
 
   @override
   void initState() {
@@ -37,33 +39,33 @@ class _MenuListState<T> extends DropdownState<DropdownListMenu<T>> {
   }
 
   Widget buildItem(BuildContext context, int index) {
-    final List<T> list = widget.data;
+    final List<T> list = widget.data!;
 
     final T data = list[index];
-    return new GestureDetector(
+    return GestureDetector(
       behavior: HitTestBehavior.opaque,
-      child: widget.itemBuilder(context, data, index == _selectedIndex),
+      child: widget.itemBuilder!(context, data, index == _selectedIndex),
       onTap: () {
         setState(() {
           _selectedIndex = index;
         });
         assert(controller != null);
-        controller.select(data, index: index);
+        controller!.select(data, index: index);
       },
     );
   }
 
   @override
   Widget build(BuildContext context) {
-    return new ListView.builder(
+    return ListView.builder(
       itemExtent: widget.itemExtent,
       itemBuilder: buildItem,
-      itemCount: widget.data.length,
+      itemCount: widget.data!.length,
     );
   }
 
   @override
-  void onEvent(DropdownEvent event) {
+  void onEvent(DropdownEvent? event) {
     switch (event) {
       case DropdownEvent.SELECT:
       case DropdownEvent.HIDE:
@@ -72,6 +74,8 @@ class _MenuListState<T> extends DropdownState<DropdownListMenu<T>> {
       case DropdownEvent.ACTIVE:
         {}
         break;
+      default:
+        break;
     }
   }
 }
@@ -92,16 +96,16 @@ class DropdownTreeMenu<T, E> extends DropdownWidget {
   final List<T> data;
 
   /// selected index of main list
-  final int selectedIndex;
+  final int? selectedIndex;
 
   /// item builder for main list
-  final MenuItemBuilder<T> itemBuilder;
+  final MenuItemBuilder<T>? itemBuilder;
 
   //selected index of sub list
-  final int subSelectedIndex;
+  final int? subSelectedIndex;
 
   /// A function to build right item of the tree
-  final MenuItemBuilder<E> subItemBuilder;
+  final MenuItemBuilder<E>? subItemBuilder;
 
   /// A callback to get sub list from left list data, eg.
   /// When you set List<MyData> to left,
@@ -112,13 +116,13 @@ class DropdownTreeMenu<T, E> extends DropdownWidget {
   final double itemExtent;
 
   /// `itemExtent` of sub list
-  final double subItemExtent;
+  final double? subItemExtent;
 
   /// background for main list
   final Color background;
 
   /// background for sub list
-  final Color subBackground;
+  final Color? subBackground;
 
   /// flex for main list
   final int flex;
@@ -128,37 +132,37 @@ class DropdownTreeMenu<T, E> extends DropdownWidget {
   final int subFlex;
 
   DropdownTreeMenu({
-    this.data,
-    double itemExtent,
+    super.key,
+    required this.data,
+    double? itemExtent,
     this.selectedIndex,
     this.itemBuilder,
     this.subItemExtent,
     this.subItemBuilder,
-    this.getSubData,
-    this.background: const Color(0xfffafafa),
+    required this.getSubData,
+    this.background = const Color(0xfffafafa),
     this.subBackground,
-    this.flex: 1,
-    this.subFlex: 2,
+    this.flex = 1,
+    this.subFlex = 2,
     this.subSelectedIndex,
-  })  : assert(getSubData != null),
-        itemExtent = itemExtent ?? kDropdownMenuItemHeight;
+  }) : itemExtent = itemExtent ?? kDropdownMenuItemHeight;
 
   @override
   DropdownState<DropdownWidget> createState() {
-    return new _TreeMenuList();
+    return _TreeMenuList<T, E>();
   }
 }
 
-class _TreeMenuList<T, E> extends DropdownState<DropdownTreeMenu> {
-  int _subSelectedIndex;
-  int _selectedIndex;
+class _TreeMenuList<T, E> extends DropdownState<DropdownTreeMenu<T, E>> {
+  int? _subSelectedIndex;
+  int? _selectedIndex;
 
   //
-  int _activeIndex;
+  int? _activeIndex;
 
-  List<E> _subData;
+  List<E>? _subData;
 
-  List<T> _data;
+  List<T>? _data;
 
   @override
   void initState() {
@@ -169,14 +173,14 @@ class _TreeMenuList<T, E> extends DropdownState<DropdownTreeMenu> {
     _data = widget.data;
 
     if (_activeIndex != null) {
-      _subData = widget.getSubData(_data[_activeIndex]);
+      _subData = widget.getSubData(_data![_activeIndex!]);
     }
 
     super.initState();
   }
 
   @override
-  void didUpdateWidget(DropdownTreeMenu oldWidget) {
+  void didUpdateWidget(DropdownTreeMenu<T, E> oldWidget) {
     // _selectedIndex = widget.selectedIndex;
     // _subSelectedIndex = widget.subSelectedIndex;
     // _activeIndex = _selectedIndex;
@@ -185,14 +189,14 @@ class _TreeMenuList<T, E> extends DropdownState<DropdownTreeMenu> {
   }
 
   Widget buildSubItem(BuildContext context, int index) {
-    return new GestureDetector(
+    return GestureDetector(
       behavior: HitTestBehavior.opaque,
-      child: widget.subItemBuilder(context, _subData[index],
+      child: widget.subItemBuilder!(context, _subData![index],
           _activeIndex == _selectedIndex && index == _subSelectedIndex),
       onTap: () {
         assert(controller != null);
-        controller.select(_subData[index],
-            index: _activeIndex, subIndex: index);
+        controller!
+            .select(_subData![index], index: _activeIndex, subIndex: index);
         setState(() {
           _selectedIndex = _activeIndex;
           _subSelectedIndex = index;
@@ -204,9 +208,9 @@ class _TreeMenuList<T, E> extends DropdownState<DropdownTreeMenu> {
   Widget buildItem(BuildContext context, int index) {
     final List<T> list = widget.data;
     final T data = list[index];
-    return new GestureDetector(
+    return GestureDetector(
       behavior: HitTestBehavior.opaque,
-      child: widget.itemBuilder(context, data, index == _activeIndex),
+      child: widget.itemBuilder!(context, data, index == _activeIndex),
       onTap: () {
         //切换
         //拿到数据
@@ -220,30 +224,30 @@ class _TreeMenuList<T, E> extends DropdownState<DropdownTreeMenu> {
 
   @override
   Widget build(BuildContext context) {
-    return new Row(
+    return Row(
       crossAxisAlignment: CrossAxisAlignment.start,
       children: <Widget>[
-        new Expanded(
+        Expanded(
             flex: widget.flex,
-            child: new Container(
-              child: new ListView.builder(
+            child: Container(
+              color: widget.background,
+              child: ListView.builder(
                 itemExtent: widget.itemExtent,
                 itemBuilder: buildItem,
-                itemCount: this._data == null ? 0 : this._data.length,
+                itemCount: this._data == null ? 0 : this._data!.length,
               ),
-              color: widget.background,
             )),
-        new Expanded(
+        Expanded(
             flex: widget.subFlex,
-            child: new Container(
+            child: Container(
               color: widget.subBackground,
-              child: new CustomScrollView(
+              child: CustomScrollView(
                 slivers: <Widget>[
-                  new SliverList(
-                      delegate: new SliverChildBuilderDelegate(
+                  SliverList(
+                      delegate: SliverChildBuilderDelegate(
                     buildSubItem,
                     childCount:
-                        this._subData == null ? 0 : this._subData.length,
+                        this._subData == null ? 0 : this._subData!.length,
                   ))
                 ],
               ),
@@ -253,7 +257,7 @@ class _TreeMenuList<T, E> extends DropdownState<DropdownTreeMenu> {
   }
 
   @override
-  void onEvent(DropdownEvent event) {
+  void onEvent(DropdownEvent? event) {
     // TODO: implement onEvent
   }
 }
diff --git a/lib/_src/dropdown_menu.dart b/lib/_src/dropdown_menu.dart
index 98f7101..4292518 100644
--- a/lib/_src/dropdown_menu.dart
+++ b/lib/_src/dropdown_menu.dart
@@ -1,5 +1,5 @@
 import 'dart:async';
-import 'dart:ui' as ui show Image, ImageFilter;
+import 'dart:ui' as ui show ImageFilter;
 import 'package:dropdown_menu/_src/drapdown_common.dart';
 import 'package:flutter/material.dart';
 
@@ -27,58 +27,55 @@ class DropdownMenu extends DropdownWidget {
   final Curve hideCurve;
 
   /// if set , background is rendered with ImageFilter.blur
-  final double blur;
+  final double? blur;
 
-  final VoidCallback onHide;
+  final VoidCallback? onHide;
 
   /// The style when one menu hide and another menu show ,
   /// see [DropdownMenuShowHideSwitchStyle]
   final DropdownMenuShowHideSwitchStyle switchStyle;
 
-  final double maxMenuHeight;
+  final double? maxMenuHeight;
 
   DropdownMenu(
-      {@required this.menus,
-      DropdownMenuController controller,
-      Duration hideDuration,
-      Duration showDuration,
+      {required this.menus,
+      DropdownMenuController? controller,
+      Duration? hideDuration,
+      Duration? showDuration,
       this.onHide,
       this.blur,
-      Key key,
+      Key? key,
       this.maxMenuHeight,
-      Curve hideCurve,
-      this.switchStyle: DropdownMenuShowHideSwitchStyle
+      Curve? hideCurve,
+      this.switchStyle = DropdownMenuShowHideSwitchStyle
           .animationShowUntilAnimationHideComplete,
-      Curve showCurve})
-      : hideDuration = hideDuration ?? new Duration(milliseconds: 150),
-        showDuration = showDuration ?? new Duration(milliseconds: 300),
+      Curve? showCurve})
+      : hideDuration = hideDuration ?? const Duration(milliseconds: 150),
+        showDuration = showDuration ?? const Duration(milliseconds: 300),
         showCurve = showCurve ?? Curves.fastOutSlowIn,
         hideCurve = hideCurve ?? Curves.fastOutSlowIn,
-        super(key: key, controller: controller) {
-    assert(menus != null);
-  }
+        super(key: key, controller: controller);
 
   @override
   DropdownState<DropdownMenu> createState() {
-    return new _DropdownMenuState();
+    return DropdownMenuState();
   }
 }
 
-class _DropdownAnimation {
-  Animation<Rect> rect;
-  AnimationController animationController;
-  RectTween position;
+class DropdownAnimation {
+  late Animation<Rect?> rect;
+  late AnimationController animationController;
+  late RectTween position;
 
-  _DropdownAnimation(TickerProvider provider) {
-    animationController = new AnimationController(vsync: provider);
+  DropdownAnimation(TickerProvider provider) {
+    animationController = AnimationController(vsync: provider);
   }
 
   set height(double value) {
-    position = new RectTween(
-      begin: new Rect.fromLTRB(0.0, -value, 0.0, 0.0),
-      end: new Rect.fromLTRB(0.0, 0.0, 0.0, 0.0),
+    position = RectTween(
+      begin: Rect.fromLTRB(0.0, -value, 0.0, 0.0),
+      end: const Rect.fromLTRB(0.0, 0.0, 0.0, 0.0),
     );
-
     rect = position.animate(animationController);
   }
 
@@ -90,7 +87,8 @@ class _DropdownAnimation {
     animationController.dispose();
   }
 
-  TickerFuture animateTo(double value, {Duration duration, Curve curve}) {
+  TickerFuture animateTo(double value,
+      {Duration? duration, required Curve curve}) {
     return animationController.animateTo(value,
         duration: duration, curve: curve);
   }
@@ -99,7 +97,7 @@ class _DropdownAnimation {
 class SizeClipper extends CustomClipper<Rect> {
   @override
   Rect getClip(Size size) {
-    return new Rect.fromLTWH(0.0, 0.0, size.width, size.height);
+    return Rect.fromLTWH(0.0, 0.0, size.width, size.height);
   }
 
   @override
@@ -108,29 +106,29 @@ class SizeClipper extends CustomClipper<Rect> {
   }
 }
 
-class _DropdownMenuState extends DropdownState<DropdownMenu>
+class DropdownMenuState extends DropdownState<DropdownMenu>
     with TickerProviderStateMixin {
-  List<_DropdownAnimation> _dropdownAnimations;
-  bool _show;
-  List<int> _showing;
+  late List<DropdownAnimation> _dropdownAnimations;
+  late bool _show;
+  late List<int> _showing;
 
-  AnimationController _fadeController;
-  Animation<double> _fadeAnimation;
+  late AnimationController _fadeController;
+  late Animation<double> _fadeAnimation;
 
   @override
   void initState() {
     _showing = [];
     _dropdownAnimations = [];
     for (int i = 0, c = widget.menus.length; i < c; ++i) {
-      _dropdownAnimations.add(new _DropdownAnimation(this));
+      _dropdownAnimations.add(DropdownAnimation(this));
     }
 
     _updateHeights();
 
     _show = false;
 
-    _fadeController = new AnimationController(vsync: this);
-    _fadeAnimation = new Tween(
+    _fadeController = AnimationController(vsync: this);
+    _fadeAnimation = Tween(
       begin: 0.0,
       end: 1.0,
     ).animate(_fadeController);
@@ -143,6 +141,7 @@ class _DropdownMenuState extends DropdownState<DropdownMenu>
     for (int i = 0, c = _dropdownAnimations.length; i < c; ++i) {
       _dropdownAnimations[i].dispose();
     }
+    _fadeController.dispose();
 
     super.dispose();
   }
@@ -150,7 +149,7 @@ class _DropdownMenuState extends DropdownState<DropdownMenu>
   void _updateHeights() {
     for (int i = 0, c = widget.menus.length; i < c; ++i) {
       _dropdownAnimations[i].height =
-          _ensureHeight(_getHeight(widget.menus[i]));
+          _ensureHeight(_getHeight(widget.menus[i]))!;
     }
   }
 
@@ -164,23 +163,23 @@ class _DropdownMenuState extends DropdownState<DropdownMenu>
   Widget createMenu(BuildContext context, DropdownMenuBuilder menu, int i) {
     DropdownMenuBuilder builder = menu;
 
-    return new ClipRect(
-      clipper: new SizeClipper(),
-      child: new SizedBox(
+    return ClipRect(
+      clipper: SizeClipper(),
+      child: SizedBox(
           height: _ensureHeight(builder.height),
           child: _showing.contains(i) ? builder.builder(context) : null),
     );
   }
 
   Widget _buildBackground(BuildContext context) {
-    Widget container = new Container(
+    Widget container = Container(
       color: Colors.black26,
     );
 
-    container = new BackdropFilter(
-        filter: new ui.ImageFilter.blur(
-          sigmaY: widget.blur,
-          sigmaX: widget.blur,
+    container = BackdropFilter(
+        filter: ui.ImageFilter.blur(
+          sigmaY: widget.blur!,
+          sigmaX: widget.blur!,
         ),
         child: container);
 
@@ -191,25 +190,25 @@ class _DropdownMenuState extends DropdownState<DropdownMenu>
   Widget build(BuildContext context) {
     List<Widget> list = [];
 
-    print("build ${new DateTime.now()}");
+    debugPrint("build ${DateTime.now()}");
 
     if (_show) {
       list.add(
-        new FadeTransition(
+        FadeTransition(
           opacity: _fadeAnimation,
-          child: new GestureDetector(
-              onTap: onHide, child: _buildBackground(context)),
+          child:
+              GestureDetector(onTap: onHide, child: _buildBackground(context)),
         ),
       );
     }
 
     for (int i = 0, c = widget.menus.length; i < c; ++i) {
-      list.add(new RelativePositionedTransition(
+      list.add(RelativePositionedTransition(
           rect: _dropdownAnimations[i].rect,
-          size: new Size(0.0, 0.0),
-          child: new Align(
+          size: const Size(0.0, 0.0),
+          child: Align(
               alignment: Alignment.topCenter,
-              child: new Container(
+              child: Container(
                 color: Theme.of(context).scaffoldBackgroundColor,
                 child: createMenu(context, widget.menus[i], i),
               ))));
@@ -217,20 +216,20 @@ class _DropdownMenuState extends DropdownState<DropdownMenu>
 
     //WidgetsBinding;
     //context.findRenderObject();
-    return new Stack(
+    return Stack(
       fit: StackFit.expand,
       children: list,
     );
   }
 
-  TickerFuture onHide({bool dispatch: true}) {
+  TickerFuture onHide({bool dispatch = true}) {
     if (_activeIndex != null) {
-      int index = _activeIndex;
+      int index = _activeIndex!;
       _activeIndex = null;
       TickerFuture future = _hide(index);
       if (dispatch) {
         if (controller != null) {
-          controller.hide();
+          controller!.hide();
         }
 
         //if (widget.onHide != null) widget.onHide();
@@ -247,7 +246,7 @@ class _DropdownMenuState extends DropdownState<DropdownMenu>
       return future;
     }
 
-    return new TickerFuture.complete();
+    return TickerFuture.complete();
   }
 
   TickerFuture _hide(int index) {
@@ -256,7 +255,7 @@ class _DropdownMenuState extends DropdownState<DropdownMenu>
     return future;
   }
 
-  int _activeIndex;
+  int? _activeIndex;
 
   Future<void> onShow(int index) {
     //哪一个是要展示的
@@ -274,7 +273,7 @@ class _DropdownMenuState extends DropdownState<DropdownMenu>
       switch (widget.switchStyle) {
         case DropdownMenuShowHideSwitchStyle.directHideAnimationShow:
           {
-            _dropdownAnimations[_activeIndex].value = 0.0;
+            _dropdownAnimations[_activeIndex!].value = 0.0;
             _dropdownAnimations[index].value = 1.0;
             _activeIndex = index;
 
@@ -282,28 +281,25 @@ class _DropdownMenuState extends DropdownState<DropdownMenu>
               _show = true;
             });
 
-            return new Future.value(null);
+            return Future.value(null);
           }
-
-          break;
         case DropdownMenuShowHideSwitchStyle.animationHideAnimationShow:
           {
-            _hide(_activeIndex);
+            _hide(_activeIndex!);
           }
           break;
         case DropdownMenuShowHideSwitchStyle.directHideDirectShow:
           {
-            _dropdownAnimations[_activeIndex].value = 0.0;
+            _dropdownAnimations[_activeIndex!].value = 0.0;
           }
           break;
         case DropdownMenuShowHideSwitchStyle
             .animationShowUntilAnimationHideComplete:
           {
-            return _hide(_activeIndex).whenComplete(() {
+            return _hide(_activeIndex!).whenComplete(() {
               return _handleShow(index, true);
             });
           }
-          break;
       }
     }
 
@@ -324,14 +320,14 @@ class _DropdownMenuState extends DropdownState<DropdownMenu>
         .animateTo(1.0, duration: widget.showDuration, curve: widget.showCurve);
   }
 
-  double _getHeight(dynamic menu) {
+  double? _getHeight(dynamic menu) {
     DropdownMenuBuilder builder = menu as DropdownMenuBuilder;
 
     return builder.height;
   }
 
-  double _ensureHeight(double height) {
-    final double maxMenuHeight = widget.maxMenuHeight;
+  double? _ensureHeight(double? height) {
+    final double? maxMenuHeight = widget.maxMenuHeight;
     assert(height != null || maxMenuHeight != null,
         "DropdownMenu.maxMenuHeight and DropdownMenuBuilder.height must not both null");
     if (maxMenuHeight != null) {
@@ -342,7 +338,7 @@ class _DropdownMenuState extends DropdownState<DropdownMenu>
   }
 
   @override
-  void onEvent(DropdownEvent event) {
+  void onEvent(DropdownEvent? event) {
     switch (event) {
       case DropdownEvent.SELECT:
       case DropdownEvent.HIDE:
@@ -352,9 +348,11 @@ class _DropdownMenuState extends DropdownState<DropdownMenu>
         break;
       case DropdownEvent.ACTIVE:
         {
-          onShow(controller.menuIndex);
+          onShow(controller!.menuIndex!);
         }
         break;
+      default:
+        break;
     }
   }
 }
diff --git a/lib/_src/dropdown_sliver.dart b/lib/_src/dropdown_sliver.dart
index 24c4173..58fbe9a 100644
--- a/lib/_src/dropdown_sliver.dart
+++ b/lib/_src/dropdown_sliver.dart
@@ -4,7 +4,7 @@ class DropdownSliverChildBuilderDelegate
     extends SliverPersistentHeaderDelegate {
   WidgetBuilder builder;
 
-  DropdownSliverChildBuilderDelegate({this.builder}) : assert(builder != null);
+  DropdownSliverChildBuilderDelegate({required this.builder});
 
   @override
   Widget build(
diff --git a/lib/_src/dropdown_templates.dart b/lib/_src/dropdown_templates.dart
index f0af4fc..3190fa3 100644
--- a/lib/_src/dropdown_templates.dart
+++ b/lib/_src/dropdown_templates.dart
@@ -1,33 +1,32 @@
-import 'package:flutter/widgets.dart';
-
 import 'package:flutter/material.dart';
 
 import 'package:dropdown_menu/_src/dropdown_header.dart';
 
 Widget buildCheckItem(BuildContext context, dynamic data, bool selected) {
-  return new Padding(
-      padding: new EdgeInsets.all(10.0),
-      child: new Row(
+  return Padding(
+      padding: const EdgeInsets.all(10.0),
+      child: Row(
         children: <Widget>[
-          new Text(
-            defaultGetItemLabel(data),
-            style: selected
-                ? new TextStyle(
-                    fontSize: 14.0,
-                    color: Theme.of(context).primaryColor,
-                    fontWeight: FontWeight.w400)
-                : new TextStyle(fontSize: 14.0),
+          Expanded(
+            child: Text(
+              defaultGetItemLabel(data)!,
+              style: selected
+                  ? TextStyle(
+                      fontSize: 14.0,
+                      color: Theme.of(context).primaryColor,
+                      fontWeight: FontWeight.w400)
+                  : const TextStyle(fontSize: 14.0),
+            ),
           ),
-          new Expanded(
-              child: new Align(
+          Align(
             alignment: Alignment.centerRight,
             child: selected
-                ? new Icon(
+                ? Icon(
                     Icons.check,
                     color: Theme.of(context).primaryColor,
                   )
                 : null,
-          )),
+          ),
         ],
       ));
 }
diff --git a/pubspec.lock b/pubspec.lock
index 33150fb..e57d118 100644
--- a/pubspec.lock
+++ b/pubspec.lock
@@ -1,34 +1,54 @@
 # Generated by pub
-# See https://www.dartlang.org/tools/pub/glossary#lockfile
+# See https://dart.dev/tools/pub/glossary#lockfile
 packages:
   async:
     dependency: transitive
     description:
       name: async
-      url: "https://pub.flutter-io.cn"
+      sha256: bfe67ef28df125b7dddcea62755991f807aa39a2492a23e1550161692950bbe0
+      url: "https://pub.dev"
     source: hosted
-    version: "2.0.8"
+    version: "2.10.0"
   boolean_selector:
     dependency: transitive
     description:
       name: boolean_selector
-      url: "https://pub.flutter-io.cn"
+      sha256: "6cfb5af12253eaf2b368f07bacc5a80d1301a071c73360d746b7f2e32d762c66"
+      url: "https://pub.dev"
     source: hosted
-    version: "1.0.4"
-  charcode:
+    version: "2.1.1"
+  characters:
     dependency: transitive
     description:
-      name: charcode
-      url: "https://pub.flutter-io.cn"
+      name: characters
+      sha256: e6a326c8af69605aec75ed6c187d06b349707a27fbff8222ca9cc2cff167975c
+      url: "https://pub.dev"
     source: hosted
-    version: "1.1.2"
+    version: "1.2.1"
+  clock:
+    dependency: transitive
+    description:
+      name: clock
+      sha256: cb6d7f03e1de671e34607e909a7213e31d7752be4fb66a86d29fe1eb14bfb5cf
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.1.1"
   collection:
     dependency: transitive
     description:
       name: collection
-      url: "https://pub.flutter-io.cn"
+      sha256: cfc915e6923fe5ce6e153b0723c753045de46de1b4d63771530504004a45fae0
+      url: "https://pub.dev"
     source: hosted
-    version: "1.14.11"
+    version: "1.17.0"
+  fake_async:
+    dependency: transitive
+    description:
+      name: fake_async
+      sha256: "511392330127add0b769b75a987850d136345d9227c6b94c96a04cf4a391bf78"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.3.1"
   flutter:
     dependency: "direct main"
     description: flutter
@@ -39,34 +59,46 @@ packages:
     description: flutter
     source: sdk
     version: "0.0.0"
+  js:
+    dependency: transitive
+    description:
+      name: js
+      sha256: "5528c2f391ededb7775ec1daa69e65a2d61276f7552de2b5f7b8d34ee9fd4ab7"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.6.5"
   matcher:
     dependency: transitive
     description:
       name: matcher
-      url: "https://pub.flutter-io.cn"
+      sha256: "16db949ceee371e9b99d22f88fa3a73c4e59fd0afed0bd25fc336eb76c198b72"
+      url: "https://pub.dev"
     source: hosted
-    version: "0.12.3+1"
+    version: "0.12.13"
+  material_color_utilities:
+    dependency: transitive
+    description:
+      name: material_color_utilities
+      sha256: d92141dc6fe1dad30722f9aa826c7fbc896d021d792f80678280601aff8cf724
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.2.0"
   meta:
     dependency: transitive
     description:
       name: meta
-      url: "https://pub.flutter-io.cn"
+      sha256: "6c268b42ed578a53088d834796959e4a1814b5e9e164f147f580a386e5decf42"
+      url: "https://pub.dev"
     source: hosted
-    version: "1.1.6"
+    version: "1.8.0"
   path:
     dependency: transitive
     description:
       name: path
-      url: "https://pub.flutter-io.cn"
+      sha256: db9d4f58c908a4ba5953fcee2ae317c94889433e5024c27ce74a37f94267945b
+      url: "https://pub.dev"
     source: hosted
-    version: "1.6.2"
-  quiver:
-    dependency: transitive
-    description:
-      name: quiver
-      url: "https://pub.flutter-io.cn"
-    source: hosted
-    version: "2.0.1"
+    version: "1.8.2"
   sky_engine:
     dependency: transitive
     description: flutter
@@ -76,58 +108,58 @@ packages:
     dependency: transitive
     description:
       name: source_span
-      url: "https://pub.flutter-io.cn"
+      sha256: dd904f795d4b4f3b870833847c461801f6750a9fa8e61ea5ac53f9422b31f250
+      url: "https://pub.dev"
     source: hosted
-    version: "1.4.1"
+    version: "1.9.1"
   stack_trace:
     dependency: transitive
     description:
       name: stack_trace
-      url: "https://pub.flutter-io.cn"
+      sha256: c3c7d8edb15bee7f0f74debd4b9c5f3c2ea86766fe4178eb2a18eb30a0bdaed5
+      url: "https://pub.dev"
     source: hosted
-    version: "1.9.3"
+    version: "1.11.0"
   stream_channel:
     dependency: transitive
     description:
       name: stream_channel
-      url: "https://pub.flutter-io.cn"
+      sha256: "83615bee9045c1d322bbbd1ba209b7a749c2cbcdcb3fdd1df8eb488b3279c1c8"
+      url: "https://pub.dev"
     source: hosted
-    version: "1.6.8"
+    version: "2.1.1"
   string_scanner:
     dependency: transitive
     description:
       name: string_scanner
-      url: "https://pub.flutter-io.cn"
+      sha256: "556692adab6cfa87322a115640c11f13cb77b3f076ddcc5d6ae3c20242bedcde"
+      url: "https://pub.dev"
     source: hosted
-    version: "1.0.4"
+    version: "1.2.0"
   term_glyph:
     dependency: transitive
     description:
       name: term_glyph
-      url: "https://pub.flutter-io.cn"
+      sha256: a29248a84fbb7c79282b40b8c72a1209db169a2e0542bce341da992fe1bc7e84
+      url: "https://pub.dev"
     source: hosted
-    version: "1.0.1"
+    version: "1.2.1"
   test_api:
     dependency: transitive
     description:
       name: test_api
-      url: "https://pub.flutter-io.cn"
-    source: hosted
-    version: "0.2.1"
-  typed_data:
-    dependency: transitive
-    description:
-      name: typed_data
-      url: "https://pub.flutter-io.cn"
+      sha256: ad540f65f92caa91bf21dfc8ffb8c589d6e4dc0c2267818b4cc2792857706206
+      url: "https://pub.dev"
     source: hosted
-    version: "1.1.6"
+    version: "0.4.16"
   vector_math:
     dependency: transitive
     description:
       name: vector_math
-      url: "https://pub.flutter-io.cn"
+      sha256: "80b3257d1492ce4d091729e3a67a60407d227c27241d6927be0130c98e741803"
+      url: "https://pub.dev"
     source: hosted
-    version: "2.0.8"
+    version: "2.1.4"
 sdks:
-  dart: ">=2.0.0 <3.0.0"
-  flutter: ">=0.1.4 <3.0.0"
+  dart: ">=2.18.0 <3.0.0"
+  flutter: ">=0.1.4"
diff --git a/pubspec.yaml b/pubspec.yaml
index a6e267b..3f80673 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,14 +1,10 @@
 name: dropdown_menu
 description: A dropdown menu for flutter.
 version: 1.1.1
-author: JZoom <jzoom8112@gmail.com>
 homepage: https://github.com/jzoom/flutter_dropdown_menu
 
-
-
-
 environment:
-  sdk: ">=2.0.0-dev.48.0 <3.0.0"
+  sdk: '>=2.17.0 <3.0.0'
   flutter: ">=0.1.4 <3.0.0"