MVVM notes

jemshit · jemshit · commit 8541f0378fe4 · 2020-10-21T15:14:59.000+03:00
diff --git a/.gitignore b/.gitignore
@@ -1,5 +1,5 @@
-
 # Created by https://www.gitignore.io/api/linux,macos,windows
+.idea/
 
 ### Linux ###
 *~
diff --git a/README.md b/README.md
@@ -10,18 +10,13 @@ General and Android specific
 ## Presentation Patterns (Delivery Mechanisms)
 ### 1. [MVC notes](https://github.com/jemshit/android_architecture_notes/blob/master/mvc_cheatsheet.md)
 
-This is not Android specific note, but MVC variants in general. So difference between these patterns can be seen.
+This is MVC variants in general (not Android specific), so difference between these patterns can be seen.
 
 ### 2. [MVP notes](https://github.com/jemshit/android_architecture_notes/blob/master/mvp_cheatsheet.md)
-Especially from Android perspective
+MVP in general and from Android perspective
 
-### 3. MVVM notes
-Not ready yet
+### 3. [MVVM notes](https://github.com/jemshit/android_architecture_notes/blob/master/mvvm_cheatsheet.md)
+MVVM in general and from Android perspective
 
 ### 4. [Pattern Differences note](https://github.com/jemshit/android_architecture_notes/blob/master/pattern_differences.md)
 MVC vs MVP vs MVVM
-
----
-- To contribute, add comment to these issues [clean architecture issue](https://github.com/jemshit/android_architecture_notes/issues/1), [mvp issue](https://github.com/jemshit/android_architecture_notes/issues/2), [mvvm issue](https://github.com/jemshit/android_architecture_notes/issues/3)
-
-- To discuss, create new issue.
diff --git a/clean_architecture_cheatsheet.md b/clean_architecture_cheatsheet.md
@@ -332,6 +332,3 @@ As you can see, it makes sense to separate "Infrastructure" (as in Onion archite
 [11] Martin Fowler, "InversionOfControl," 26 06 2005. [Online]. Available: https://martinfowler.com/bliki/InversionOfControl.html. [Accessed 02 03 2018]
 
 [12] Martin Fowler, "Registry," [Online]. Available: https://martinfowler.com/eaaCatalog/registry.html. [Accessed 02 03 2018]
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-Last Edited: 05.03.2018
diff --git a/media_files/mvvm.png b/media_files/mvvm.png
diff --git a/media_files/mvvm_viewmodel_scope.png b/media_files/mvvm_viewmodel_scope.png
diff --git a/mvc_cheatsheet.md b/mvc_cheatsheet.md
@@ -126,6 +126,3 @@ Figure reference: [[6]](#4-references)
 [5] Stephen Walther, "The Evolution of MVC," 24 08 2008. [Online]. Available: http://stephenwalther.com/archive/2008/08/24/the-evolution-of-mvc. [Accessed 02 03 2018].
 
 [6] Manoj Jaggavarapu, "Presentation Patterns : MVC, MVP, PM, MVVM," 02 05 2012. [Online]. Available: https://manojjaggavarapu.wordpress.com/2012/05/02/presentation-patterns-mvc-mvp-pm-mvvm/. [Accessed 03 03 2018].
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-Last Edited: 04.03.2018
diff --git a/mvp_cheatsheet.md b/mvp_cheatsheet.md
@@ -314,7 +314,3 @@ https://overflow.buffer.com/2017/12/21/even-map-though-data-model-mapping-androi
 [19] "What are MVP and MVC and what is the difference?," [Online]. Available: https://stackoverflow.com/a/101561/3736955. [Accessed 03 03 2018].
 
 [20] Jose Alcérreca, "ViewModels and LiveData: Patterns + AntiPatterns," [Online]. Available: https://medium.com/@JoseAlcerreca/yep-if-you-use-viewmodel-as-a-presenter-you-need-a-reference-to-the-view-b853879ccd0e. [Accessed 21 03 2018].
-
-
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-Last Edited: 04.03.2018
diff --git a/mvvm_cheatsheet.md b/mvvm_cheatsheet.md
@@ -0,0 +1,73 @@
+# MVVM (Model-View-ViewModel)
+
+"Model/View/ViewModel is a variation of Model/View/Controller (MVC) that is tailored for modern UI development platforms
+where the View is the responsibility of a designer rather than a classic developer.
+The designer is generally a more graphical, artistic focused person, and does less classic coding than a traditional developer..
+The design is almost always done in a declarative form like HTML or XAML.." [[8]](#references)
+
+![MVVM](https://raw.githubusercontent.com/jemshit/android_architecture_notes/master/media_files/mvvm.png)
+[[1]](#references)
+
+- "Model-View-ViewModel is an architectural approach used to **abstract the state and behaviour of a view**, which allows us to **separate the development of the UI from the business logic.**" [[2]](#references)
+- "This is accomplished by the introduction of a ViewModel, whose responsibility is to expose the data objects of a model and handle any of the application logic involved in the display of a view." [[2]](#references)
+
+## 1. Model
+
+- "Data model containing business and validation logic" [[1]](#references) [[2]](#references)
+- Does not contain any View reference or View related logic
+
+
+## 2. View
+
+- "Defines the structure, layout and appearance of a view on screen" [[2]](#references)
+- "View in MVVM is similar to view in PM. It contains only the UI elements. The interaction between view and ViewModel happens using Data Binding, Commands and Notifications..." [[1]](#references)
+- "..ViewModel only provides the data, whereas the View is responsible for consuming them." [[5]](#references)
+- In Android, View can consume data using _LifecycleOwner_ and _LiveData_ classes, which stops observing (unsubscribes/disposes) the data at corresponding lifecycles automatically
+- "Even if the View gets to decide how to handle data, that does not mean it needs to contain complicated logic. The idea is that ViewModel provides data in a form that View **simply takes and display** - no manipulation required." [[5]](#references)
+
+
+## 3. ViewModel
+
+- "Acts a link between the View and Model, dealing with any view logic" [[2]](#references)
+- "ViewModel does not hold reference to the View" [[5]](#references)[[7]](#references)
+- "View Model is equivalent to PresentationModel in PM pattern, it encapsulates presentation logic and data for the view.  ViewModel contains the state of the view and uses Commands, DataBinding and Notifications to communicate with the view." [[1]](#references)
+- "Keep the ViewModel free of Android Dependencies...This allows me to utilize JUnit unit tests for a quick feedback loop" [[3]](#references)[[7]](#references)
+- "ViewModels hold **transient data used in the UI**, but they don’t persist data" [[6]](#references)
+- ViewModel class offered by Android survives configuration change (screen rotation) (using Retaining Fragment under the hood). So it can hold UI state [[4]](#references)[[5]](#references)[[7]](#references)
+
+![MVVM](https://raw.githubusercontent.com/jemshit/android_architecture_notes/master/media_files/mvvm_viewmodel_scope.png)
+[[4]](#references)
+
+- For one-off events (like Toast message), PublishSubject (RxJava) or SingleLiveEvent (Lifecycle Components) [[7]](#references) classes can be used. 
+- It can be used by multiple Views
+- ViewModel can expose _ObservableInterface<DataState<Data>>_ to hold information about loading, success, error instead of just data. [[7]](#references)
+
+
+### DataBinding
+
+Pros:
+- Reduces boilerplate, because it binds view and logic directly without middle man
+
+Cons:
+- In Android, requires full package name to ViewModel class in XML
+- In Android, containing logic in XML is not good, it makes testing difficult. Instead, these logics can be moved to custom _BindingAdapters_ [[3]](#references)
+- If you want to have click listener for Android View, function in ViewModel has to return _View.OnClickListener_, which forces ViewModel to have Android code
+
+
+### References
+
+[1] Manoj Jaggavarapu, "Presentation Patterns : MVC, MVP, PM, MVVM," 02 05 2012. [Online]. Available: https://manojjaggavarapu.wordpress.com/2012/05/02/presentation-patterns-mvc-mvp-pm-mvvm/. [Accessed 03 03 2018].
+
+[2] Joe Birch, "Approaching Android with MVVM" 21 09 2015. [Online]. Available: https://labs.ribot.co.uk/approaching-android-with-mvvm-8ceec02d5442. [Accessed 21 10 2020].
+
+[3] Donn Felker, "Android MVVM with DataBinding – Removing Logic from Your Views with BindingAdapters". [Online]. Available: https://www.donnfelker.com/android-mvvm-with-databinding-removing-logic-from-your-views-with-bindingadapters/. [Accessed 21 10 2020].
+
+[4] Luis G. Valle, "Firebase, ViewModels & LiveData" 22 10 2017. [Online]. Available: https://medium.com/@lgvalle/firebase-viewmodels-livedata-cb64c5ee4f95. [Accessed 21 10 2020].
+
+[5] Kamil Seweryn, "MVP to MVVM transformation" 20 01 2018. [Online]. Available: https://proandroiddev.com/mvp-to-mvvm-transformation-611959d5e0ca. [Accessed 21 10 2020].
+
+[6] Lyla Fujiwara, "ViewModels: Persistence, onSaveInstanceState(), Restoring UI State and Loaders" 17 07 2017. [Online]. Available: https://medium.com/androiddevelopers/viewmodels-persistence-onsaveinstancestate-restoring-ui-state-and-loaders-fc7cc4a6c090. [Accessed 21 10 2020].
+
+[7] Jose Alcérreca, "ViewModels and LiveData: Patterns + AntiPatterns" 12 09 2017. [Online]. Available: https://medium.com/androiddevelopers/viewmodels-and-livedata-patterns-antipatterns-21efaef74a54. [Accessed 21 10 2020].
+
+[8] John Gossman, "Introduction to Model/View/ViewModel pattern for building WPF apps" 08 10 2015. [Online]. Available: https://docs.microsoft.com/en-us/archive/blogs/johngossman/introduction-to-modelviewviewmodel-pattern-for-building-wpf-apps. [Accessed 21 10 2020].
diff --git a/mvvm_cheatsheet_draft.md b/mvvm_cheatsheet_draft.md
diff --git a/pattern_differences.md b/pattern_differences.md
@@ -73,6 +73,8 @@ that the loading animation should be displayed now or that the ListView should b
 
 - You’ll also notice that the View has no idea about the Model in the MVVM pattern. This is because, as far as the View knows, its “Model” IS the View Model (hence its name). Because of how data-binding and other features like commanding work in WPF and Silverlight, there is rich communication between the View and View Model, isolating the View from having to know anything about what’s really happening behind the scenes." [[1]](#3-references)
 
+- "..ViewModel only provides the data, whereas the View is responsible for consuming them." [[7]](#references)
+
 #### d) PM
 Presentation Model definition: https://martinfowler.com/eaaDev/PresentationModel.html
 
@@ -90,5 +92,4 @@ Presentation Model definition: https://martinfowler.com/eaaDev/PresentationModel
 
 [6] Martin Fowler, "GUI Architectures," 18 07 2006. [Online]. Available: https://martinfowler.com/eaaDev/uiArchs.html. [Accessed 26 02 2018].
 
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-Last Edited: 04.03.2018
+[7] Kamil Seweryn, "MVP to MVVM transformation" 20 01 2018. [Online]. Available: https://proandroiddev.com/mvp-to-mvvm-transformation-611959d5e0ca. [Accessed 21 10 2020].
