MVVM on Android - Berlindroid

MVVM is a design pattern for architecting applications that have become popular on Android.

In this talk, we will look at what is MVVM and how to use ArchitectureComponents with them, and share my experience on how I build robust, maintainable and testable apps using them.

- What is MVVM
- How it differs from other design patterns
- Learn how to do MVVM with Architecture Components
- A brief look at testing
- Advantages

Transcript

1. @AkshayChordiya MVVM on Android
2. And I love cooking!
3. 3 MV* Model represents data, and business logic View presents information that it retrieves from one or more model objects Model View
4. 4 MVVM Model represents data, and business logic View presents information that it observes from one or more ViewModel objects Model View ViewModel Interacts with model and on change notifies the view to update User Action Observes Request data Expose data
5. Introducing Architecture Components
6. 6 Lifecycle LiveData ViewModel Room WorkManager Navigation Paging
7. 7 Lifecycle LiveData ViewModel Room
8. Helps you build lifecycle-aware components Lifecycle
9. Lifecycle LifecycleObserver [e.g. LiveData] LifecycleOwner [Activity / Fragment] LifecycleOwners are ViewController with their own lifecycle LifecycleObserver observe LifecycleOwners and are notified about lifecycle changes
10. Why is this useful?
11. Useful for cases like analytics
12. 12 class AnalyticsObserver : LifecycleObserver { }
13. 13 class AnalyticsObserver : LifecycleObserver { @OnLifecycleEvent(Lifecycle.Event.ON_CREATE) fun trackOpenEvent() { Timber.d(“onCreate: Send open event") } @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY) fun trackCloseEvent() { Timber.d(“onDestroy: Send close event”) } }
14. Under the hood Lifecycle
15. 15 onDestroy DESTROYED INITIALIZED CREATED STARTED RESUMED onStop onPause onStart onCreate onResume
16. Instantly notifies the changes in the data to the UI LiveData
17. 17 LiveData value updates Observe for updates Is STARTED or RESUMED? Notify the observer Update the UI
18. They decouple the data from the View to survive configuration change ViewModel
20. Let’s try with ViewModel
21. 21 class CounterViewModel : ViewModel() { }
22. 22 class CounterViewModel : ViewModel() { var counter: MutableLiveData<Int> = MutableLiveData() init { counter.value = 0 } } Emits data
23. 23 class CounterViewModel : ViewModel() { var counter: MutableLiveData<Int> = MutableLiveData() init { counter.value = 0 } fun increment() { counter.value = counter.value?.inc() } } Emits data Emits data
24. 24 // Get the ViewModel in [Activity, Fragment] val counterViewModel = ViewModelProviders.of(this) .get(CounterViewModel::class.java)
25. 25 // Get the ViewModel in [Activity, Fragment] val counterViewModel = ViewModelProviders.of(this) .get(CounterViewModel::class.java) // Observe the `LiveData` for changes counterViewModel.counter.observe(this, Observer { count.text = counterViewModel.counter.toString() })
26. 26 // Get the ViewModel in [Activity, Fragment] val counterViewModel = ViewModelProviders.of(this) .get(CounterViewModel::class.java) // Observe the `LiveData` for changes counterViewModel.counter.observe(this, Observer { count.text = counterViewModel.counter.toString() }) // Increment the count increment.setOnClickListener { counterViewModel.increment() }
27. Under the hood ViewModel
28. Activity created onCreate onStart onResume ViewModel Scope
29. ViewModel Scope Activity created Activity rotated onCreate onStart onResume onPause onStop onCreate onDestroy onStart onResume
30. onCleared() ViewModel Scope Activity created Activity rotated finish() Finished onCreate onStart onResume onPause onStop onCreate onDestroy onStart onResume onPause onStop onDestroy
31. “Never reference to context or views in the ViewModel”
32. Under the hood LiveData
33. onCleared() Activity created Activity rotated finish() Finished onCreate onStart onStop onCreate onDestroy onStart onResume onPause onStop onDestroy 0 0 1 1 2 onPause onResume 3 3
34. Don’t try to scale it outside the presentation layer…kinda
35. Helps persist ViewModel state across process death SavedState ALPHA
36. 36 override fun onCreate(savedInstanceState: Bundle?) { // ... // Get ID val id = savedInstanceState?.getInt("id", 0) viewModel.setId(id) // Observe the data from ViewModel viewModel.getData().observe(...) } override fun onSaveInstanceState(outState: Bundle?) { outState?.putInt("id", someId) super.onSaveInstanceState(outState) }
37. 37 override fun onCreate(savedInstanceState: Bundle?) { // ... // Get the ViewModel in [Activity, Fragment] val detailViewModel = ViewModelProviders.of( this, SavedStateVMFactory(this) ).get(DetailViewModel::class.java) }
38. 38 override fun onCreate(savedInstanceState: Bundle?) { // ... // Get the ViewModel in [Activity, Fragment] val detailViewModel = ViewModelProviders.of( this, SavedStateVMFactory(this) ).get(DetailViewModel::class.java) // Get ID viewModel.setId(id) // Observe the data from ViewModel viewModel.getData().observe(...) }
39. 39 class DetailViewModel( private val savedState: SavedStateHandle ) : ViewModel() { fun getData(): LiveData<Data> = // Restore data fun setId(id: Int) { // Save id savedState.set("id", id) } }
40. Guide to MVVM
41. 41 UI Controller [Activity / Fragment] ViewModel Repository Model Remote Data Source SQLite webservice All things related to View like rendering Holds data required by UI
42. 42 UI Controller [Activity / Fragment] Repository Model Remote Data Source SQLite webservice ViewModel LiveData LiveData LiveData Room Retrofit
43. “Don’t reference ViewModel in Repository or UseCases”
44. Use Transformations
45. Perks
46. <insert perks here>
47. Testing
48. Testing Component Tests Mock UI Espresso ViewModel ViewModel JUnit Repository Repository JUnit DAO and WebService DAO Instrumented - WebService Instrumented MockWebServer
49. This is a architecture not the architecture
50. Show case project https://github.com/AkshayChordiya/android-arch-news-sample
51. www.helloclue.com Thank you foodies! @AkshayChordiya