MVVM, Viewmodel and architecture components

UAmobile, Kiev

Transcript

1. #UAMOBILE ViewMODEL & MVVM & databinding architecture components in ACTION @PreusslerBerlin
3. Introducing The architecture components
4. starring Room LiFe cycle LiveData ViewModel Pagination (new)
5. in new suggested architecture
6. in new suggested architecture
7. In architecture components •A ViewModel provides the data for a specific UI •The ViewModel does not know about the View! •Survives configuration change
8. In architecture components •A ViewModel provides the data for a specific UI •The ViewModel does not know about the View! •Survives configuration change
9. In architecture components •A ViewModel provides the data for a specific UI •The ViewModel does not know about the View! •Survives configuration change
10. In architecture components •A ViewModel provides the data for a specific UI •The ViewModel does not know about the View! •Survives configuration change
11. In architecture components •Remember configuration change can be: •Rotation •Any other resize i.e. split screen •Language change
12. life cycle: rotation onCreate onStart onResume onPause onStop onDestroy onCreate onStart onResume ViewModel
13. life cycle: finish onCreate onStart onResume onPause onStop onDestroy ViewModel
14. How to use implementation 'android.arch.lifecycle:extensions:1.0.0’ kapt 'android.arch.lifecycle:compiler:1.0.0’
15. How to use class MyViewModel() : ViewModel() {
16. How to use class MyViewModel(app: Application) : AndroidViewModel(app) {
17. How to use override fun onCreate(...) { model = ViewModelProviders .of(this) .get(MyViewModel::class.java) }
18. What if… constructor arguments needed?
19. How to use class MyViewModelFactory :ViewModelProvider.Factory(useCase: MyUseCase) { fun <T: ViewModel> create(aClass: Class<T>): T { return MyViewModel(useCase) as T } }
20. How to use ViewModelProviders .of(this, MyViewModelFactory(usecase)) .get(MyShowsViewModel::class.java)
21. How to use •Always try to build your own Factory •Default factory uses newInstance() which is some hundred times slower than new calls (reflection) https://speakerdeck.com/dpreussler/comparing-dependency-injection- frameworks-and-internals-for-android
22. How to use •Always try to build your own Factory •Default factory uses newInstance() which is some hundred times slower than new calls (reflection) https://speakerdeck.com/dpreussler/comparing-dependency-injection- frameworks-and-internals-for-android
23. How to use override fun onStopped() { … } No more life cycle forwarding!
24. What if… I need to clean something when destroyed?
25. What if… class MyViewModel() : ViewModel() { override fun onCleared() { super.onCleared() cleanupSubscriptions() }
26. How does it survive orientation change?
27. How does it actually work? class HolderFragment extends Fragment { public HolderFragment() { setRetainInstance(true); } …
28. How does it actually work? String HOLDER_TAG = "android.arch.lifecycle.state.StateProviderH olderFragment";
29. How does it know the activity is finishing?
30. How does it actually work? @Override public void onDestroy() { super.onDestroy(); mViewModelStore.clear(); }
31. Can I do it differently? ViewModel is not life cycle aware?
32. It just refuses to die
33. remember Never hold View or Activity references in the ViewModel!
34. Tell us more
35. What if Two Fragments of same Activity ask for same ViewModel.class via ViewModelProviders .of(this) .get(MyViewModel::class.java)
36. Different ViewModels RESULT
37. What if Two Fragments of same Activity ask for same ViewModel.class via ViewModelProviders .of(this) .get(MyViewModel::class.java)
38. W A I T
39. result •Fragment and Activity share the same FragmentManager •But implementation uses Activity’s FragmentManager but ChildFragmentManager for Fragments
40. result •Fragment and Activity share the same FragmentManager •But implementation uses Activity’s FragmentManager but ChildFragmentManager for Fragments
41. What if Two Fragments of same Activity ask for same ViewModel.class via ViewModelProviders .of(getActivity()) .get(MyViewMode::class).java
42. result Same ViewModel
43. Tell us more
44. Other uses cases communication layer between activities and fragments or fragments and fragments
45. Other uses cases Replace Loaders (plus Room and LiveData/Rx)
46. Tell us more
47. ViewModel like in Model-View-ViewModel ?
48. Model-View-ViewModel
49. ViewModel in MVVM world Model ViewModel View View Presenter Model
50. ViewModel in MVVM world Model ViewModel View View ViewModel Model
51. Is MVP dead?
52. Is MVP dead? It’s like Java and Kotlin: •MVP will stay for quite some time •There is a new cooler kid in town that won’t leave
53. Is MVP dead? It’s like Java and Kotlin: •MVP will stay for quite some time •There is a new cooler kid in town that won’t leave
54. Is MVP dead? It’s like Java and Kotlin: •MVP will stay for quite some time •There is a new cooler kid in town that won’t leave
55. Is MVP dead? •Start by putting the ViewModel behind Presenter
56. Binding to ViewMODELS Activity Activity ViewModel (un)bind (un)bind
57. IntroduciNG LIVE DATA Activity Activity LiveData LiveData ViewModel
58. IntroduciNG LIVE DATA •Observable similar to RxJava •Life cycle aware •Doesn’t emit when not needed •Memory leaks save
59. IntroduciNG LIVE DATA class MyViewModel(): ViewModel() { val message = MutableLiveData<String>()
60. IntroduciNG LIVE DATA myModel.message.observe( this, Observer { display(it) })
61. Is there something better?
62. Databinding!
63. Data binding full picture XML ViewModel bind
64. Solves the one big android question once and forever who is the view?
65. ViewModel in data binding <TextView … android:id="@+id/all_shows_item_title" android:text="@{viewModel.title}" /> <data> <variable name="viewModel" type="com.vmn.playplex.main.allshows.AllShowsViewModel"/> </data>
66. ViewModel in data binding <android.support.v7.widget.CardView … android:onClick="@{() -> viewModel.onClicked()}"> <data> <variable name="viewModel" type="com.vmn.playplex.main.allshows.AllShowsViewModel"/> </data>
67. How to use class AllShowsViewModel: ViewModelObservable() { var title : CharSequence = ""
68. How to use class AllShowsViewModel: ViewModelObservable() { @Bindable var title : CharSequence = "" private set(value) { if (field != value) { field = value notifyPropertyChanged(BR.title) } }
69. How to use class AllShowsViewModel: ViewModelObservable() { @Bindable var title by bindable<CharSequence>("") private set Custom property delegate
70. How to use class AllShowsFragment : Fragment () { @Inject lateinit var showsViewModel: AllShowsViewModel
71. How to use class AllShowsFragment : Fragment () { @Inject lateinit var showsViewModel: AllShowsViewModel override fun onCreateView(…):View? =
72. How to use class AllShowsFragment : Fragment () { @Inject lateinit var showsViewModel: AllShowsViewModel override fun onCreateView(…):View? = FragmentShowsBinding.inflate( inflater, container, false).apply { viewModel = showsViewModel }).root
73. How to use class AllShowsFragment : Fragment () { @Inject lateinit var showsViewModel: AllShowsViewModel override fun onCreateView(…):View? = FragmentShowsBinding.inflate( inflater, container, false).apply { viewModel = showsViewModel }).root fragment_shows.xml
74. How to use class MyViewModel() :ViewModelObservable() { Coming soon Jose Alcérreca, Google https://medium.com/@dpreussler/add-the-new-viewmodel-to-your-mvvm-36bfea86b159
75. How do I…
76. .. show a toast class SeriesViewModel : Viewmodel() { … @Bindable var error = ObservableField<String>()
77. .. show a toast viewModel.error.addOnPropertyChangedCallback( object : OnPropertyChangedCallback() { override fun onPropertyChanged(…) { showToast(viewModel.error.get() } })
78. .. show a toast (alternative) <FrameLayout app:showError="@{viewModel.error}"> @BindingAdapter("showError") fun ViewGroup.onErrorAppeared(error: String?){ errorString?.let { showToast(context, error)) } }
79. Data binding full picture XML Activity ViewModel (un)bind bind Life cycle aware class (un)bind
80. WAYS TO OBSERVE DATA from VM? •Data binding Observable from xml or code, might need unregister •RxJava Observable from code, needs unregister •LiveData Observable, from code, no unregister, life cycle aware
81. let`s sum up •Architecture components are here •Use the parts you need •Goal: common architecture language •Databinding rocks •Know about life cycle
82. Want to know more • https://medium.com/@dpreussler/add-the-new- viewmodel-to-your-mvvm-36bfea86b159 • https://proandroiddev.com/customizing-the-new- viewmodel-cf28b8a7c5fc • http://hannesdorfmann.com/android/arch-components- purist • https://blog.stylingandroid.com/architecture-components- viewmodel/ • https://www.youtube.com/watch?v=QrbhPcbZv0I • https://www.youtube.com/watch?v=c9-057jC1ZA
83. Southpark copyright Disclaimer
84. viacom.tech
85. View Model IN ACTION @PreusslerBerlin
86. Does that mean all problems are solved?
87. all problems solved? ViewModels provide a convenient way to retain data across configuration changes but they are not persisted if the application is killed by the operating system https://developer.android.com/topic/libraries/architecture/viewmodel.html#viewm odel_vs_savedinstancestate
88. but but WHY?
89. Why? The data saved via onSaveInstanceState is kept in the system process memory and the Android OS allows you to keep only a very small amount of data so it is not a good place to keep actual data for your app. TransactionTooLargeException anyone?
90. MeaNS ViewModels gives us rotation But takes away recreation
91. after The truth •Keep non-UI states in non-UI layer Not in bundle! •Use real caching strategies •Allows updating cache in background
92. after The truth •Keep non-UI states in non-UI layer Not in bundle! •Use real caching strategies •Allows updating cache in background
93. after The truth •Keep non-UI states in non-UI layer Not in bundle! •Use real caching strategies •Allows updating cache in background
94. but but EditText might have restored it’s state but the ViewModel will not now about it
95. but but Where to store the UI state?
96. store the UI state In Bundles!
97. but but Who owns the UI state?
98. store the UI state The ViewModel
99. store the UI state
100. lets tweak it class MyModelFactory(val bundle: Bundle?) :ViewModelProvider.Factory() { … fun <T: ViewModel> create(aClass: Class<T>): T { return MyViewModel().apply { readFrom(bundle) } as T } ...
101. lets tweak it override onSaveInstanceState(bundle: Bundle){ super.onSaveInstanceState(bundle); viewModel.writeTo(bundle); }