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Fix System.OverflowException in CustomScrollViewerEx during Mouse Wheel scroll #4497

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Fix System.OverflowException in CustomScrollViewerEx during Mouse Wheel scroll #4497

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57c4eb6
fix: avoid calculating WheelChange when actual height is zero
4yinn May 29, 2026
4fa1f3d
fix: adjustment
4yinn May 29, 2026
fc0fd3c
Update Flow.Launcher/Resources/Controls/CustomScrollViewerEx.cs
4yinn May 31, 2026
ff7d7f7
change location check to ActualHeight validation
4yinn Jun 1, 2026
7e3aa4a
Merge branch 'dev' into hotfix/fix-overflow-scrolling
4yinn Jun 1, 2026
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1 change: 1 addition & 0 deletions Flow.Launcher.Test/Flow.Launcher.Test.csproj
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Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,7 @@
</ItemGroup>

<ItemGroup>
<ProjectReference Include="..\Flow.Launcher\Flow.Launcher.csproj" />
<ProjectReference Include="..\Plugins\Flow.Launcher.Plugin.Calculator\Flow.Launcher.Plugin.Calculator.csproj" />
<ProjectReference Include="..\Plugins\Flow.Launcher.Plugin.Explorer\Flow.Launcher.Plugin.Explorer.csproj" />
<ProjectReference Include="..\Plugins\Flow.Launcher.Plugin.Program\Flow.Launcher.Plugin.Program.csproj" />
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36 changes: 36 additions & 0 deletions Flow.Launcher.Test/MouseWheelTest.cs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,36 @@
using System;
using System.Reflection;
using System.Windows;
using System.Windows.Input;
using System.Windows.Interop;
using Flow.Launcher.Resources.Controls;
using NUnit.Framework;

namespace Flow.Launcher.Test;

[TestFixture]
public class MouseWheelTest
{
[Test]
[RequiresThread(System.Threading.ApartmentState.STA)]
public void Test_Scroll_MouseWheel()
{
var scrollView = new CustomScrollViewerEx();

var mouseDevice = Mouse.PrimaryDevice;
var e = new MouseWheelEventArgs(mouseDevice, Environment.TickCount, 120)
{
RoutedEvent = UIElement.MouseWheelEvent
};

var onMouseWheelMethod = typeof(CustomScrollViewerEx).GetMethod(
"OnMouseWheel",
BindingFlags.NonPublic | BindingFlags.Instance
);

Assert.DoesNotThrow(() =>
{
onMouseWheelMethod.Invoke(scrollView, new object[] { e });
});
Comment on lines +26 to +34
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@coderabbitai coderabbitai Bot May 29, 2026

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⚠️ Potential issue | 🟡 Minor | ⚡ Quick win

Assert reflected method lookup before invocation.

Add an explicit null assertion for onMouseWheelMethod so failures are diagnostic (method not found) instead of a generic null-reference during invoke.

Suggested fix 
         var onMouseWheelMethod = typeof(CustomScrollViewerEx).GetMethod(
             "OnMouseWheel",
             BindingFlags.NonPublic | BindingFlags.Instance
         );
+        Assert.That(onMouseWheelMethod, Is.Not.Null, "OnMouseWheel method was not found via reflection.");
 
         Assert.DoesNotThrow(() =>
         {
             onMouseWheelMethod.Invoke(scrollView, new object[] { e });
         });
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
var onMouseWheelMethod = typeof(CustomScrollViewerEx).GetMethod(
"OnMouseWheel",
BindingFlags.NonPublic | BindingFlags.Instance
);
Assert.DoesNotThrow(() =>
{
onMouseWheelMethod.Invoke(scrollView, new object[] { e });
});
var onMouseWheelMethod = typeof(CustomScrollViewerEx).GetMethod(
"OnMouseWheel",
BindingFlags.NonPublic | BindingFlags.Instance
);
Assert.That(onMouseWheelMethod, Is.Not.Null, "OnMouseWheel method was not found via reflection.");
Assert.DoesNotThrow(() =>
{
onMouseWheelMethod.Invoke(scrollView, new object[] { e });
});
🤖 Prompt for AI Agents 
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@Flow.Launcher.Test/MouseWheelTest.cs` around lines 26 - 34, The reflection
lookup for CustomScrollViewerEx's "OnMouseWheel" is not asserted before Invoke,
which causes a confusing null-reference if the method isn't found; add an
explicit null assertion (e.g. Assert.IsNotNull or Assert.NotNull) for
onMouseWheelMethod after the GetMethod call with a clear message like
"OnMouseWheel method not found on CustomScrollViewerEx" so failures are
diagnostic, then proceed to call onMouseWheelMethod.Invoke(scrollView, new
object[] { e }) inside the existing Assert.DoesNotThrow block.

}
}
15 changes: 10 additions & 5 deletions Flow.Launcher/Resources/Controls/CustomScrollViewerEx.cs
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Expand Up @@ -17,7 +17,8 @@ public class CustomScrollViewerEx : ScrollViewer
public CustomScrollViewerEx()
{
Loaded += OnLoaded;
var valueSource = DependencyPropertyHelper.GetValueSource(this, AutoPanningMode.IsEnabledProperty).BaseValueSource;
var valueSource = DependencyPropertyHelper.GetValueSource(this, AutoPanningMode.IsEnabledProperty)
.BaseValueSource;
if (valueSource == BaseValueSource.Default)
{
AutoPanningMode.SetIsEnabled(this, true);
Expand Down Expand Up @@ -45,9 +46,9 @@ public Orientation Orientation

public static readonly DependencyProperty AutoHideScrollBarsProperty =
ScrollViewerHelper.AutoHideScrollBarsProperty
.AddOwner(
typeof(CustomScrollViewerEx),
new PropertyMetadata(true, OnAutoHideScrollBarsChanged));
.AddOwner(
typeof(CustomScrollViewerEx),
new PropertyMetadata(true, OnAutoHideScrollBarsChanged));

public bool AutoHideScrollBars
{
Expand Down Expand Up @@ -86,6 +87,9 @@ protected override void OnInitialized(EventArgs e)
/// <inheritdoc/>
protected override void OnMouseWheel(MouseWheelEventArgs e)
{
if (ActualHeight <= 0)
return;

var Direction = GetDirection();
ScrollViewerBehavior.SetIsAnimating(this, true);

Expand Down Expand Up @@ -196,7 +200,8 @@ public bool ChangeView(double? horizontalOffset, double? verticalOffset, float?
/// <param name="zoomFactor">A value between MinZoomFactor and MaxZoomFactor that specifies the required target ZoomFactor.</param>
/// <param name="disableAnimation"><see langword="true"/> to disable zoom/pan animations while changing the view; otherwise, <see langword="false"/>. The default is false.</param>
/// <returns><see langword="true"/> if the view is changed; otherwise, <see langword="false"/>.</returns>
public bool ChangeView(double? horizontalOffset, double? verticalOffset, float? zoomFactor, bool disableAnimation)
public bool ChangeView(double? horizontalOffset, double? verticalOffset, float? zoomFactor,
bool disableAnimation)
{
if (disableAnimation)
{
Expand Down
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