Viewmodel and friends: DevFest Budapest 2017

Talk about new Architecture components: Viewmodel, Lifecycle, LiveData. The role of MVVM, RxJava...

1. DEVFEST BUDAPEST ViewMODEL AND FRIENDS the new architecture components @PreusslerBerlin
3. The ”architecture components”
4. The ”architecture components” •Room •Lifecycle Observer •LiveData •ViewModel •New: Pagination
5. The ”architecture components” •Room •Lifecycle Observer •LiveData •ViewModel •New: Pagination
6. The ”architecture components” ViewModel like in Model-View-ViewModel ViewModel?
7. ViewModel in MVVM world
8. ViewModel in data binding Rx XML ViewModel
9. ViewModel in data binding <TextView … android:id="@+id/all_shows_item_title" android:text="@{viewModel.title}" /> <android.support.v7.widget.CardView … android:onClick="@{() -> viewModel.onClicked()}"> <data> <variable name="viewModel" type="com.vmn.playplex.main.allshows.SeriesViewModel"/> </data>
10. in new suggested architecture
11. in new suggested architecture
12. Is MVP dead?
13. 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 Put the ViewModel behind Presenter
14. 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 Put the ViewModel behind Presenter
15. 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 Put the ViewModel behind Presenter
16. 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 Put the ViewModel behind Presenter
17. In architecture components •A ViewModel provides the data for a specific UI •The ViewModel does not know about the View! •Survives configuration change
18. In architecture components •A ViewModel provides the data for a specific UI •The ViewModel does not know about the View! •Survives configuration change
19. In architecture components •A ViewModel provides the data for a specific UI •The ViewModel does not know about the View! •Survives configuration change
20. In architecture components •A ViewModel provides the data for a specific UI •The ViewModel does not know about the View! •Survives configuration change
21. In architecture components •Remember configuration change can be: •Rotation •Any other resize i.e. split screen •Language change
22. life cycle: rotation onCreate onStart onResume onPause onStop onDestroy onCreate onStart onResume ViewModel
23. life cycle: finish onCreate onStart onResume onPause onStop onDestroy ViewModel
24. How to use compile 'android.arch.lifecycle:runtime:1.0.0-beta1' compile 'android.arch.lifecycle:extensions:1.0.0-beta1’ kapt 'android.arch.lifecycle:compiler:1.0.0-beta1
25. How to use class MyViewModel() : ViewModel() {
26. How to use class MyViewModel(app: Application) : AndroidViewModel(app) {
27. How to use class MyViewModel() :ViewModelObservable() { Coming soon Jose Alcérreca, Google https://medium.com/@dpreussler/add-the-new-viewmodel-to-your-mvvm-36bfea86b159
28. How to use override fun onStopped() { … } No more life cycle forwarding!
29. How to use override fun onCreate(...) { model = ViewModelProviders .of(this) .get(MyViewModel::class.java) }
30. What if… constructor arguments needed?
31. How to use class MyViewModelFactory :ViewModelProvider.Factory(useCase: MyUseCase) { fun <T: ViewModel> create(aClass: Class<T>): T { return MyViewModel(useCase) as T } }
32. How to use ViewModelProviders .of(this, MyViewModelFactory(usecase)) .get(MyShowsViewModel::class.java)
33. 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
34. 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
35. What if… I need to clean something when destroyed?
36. What if… class MyViewModel() : ViewModel() { override fun onCleared() { super.onCleared() cleanupSubscriptions() }
37. How does it survive orientation change?
38. How does it actually work? class HolderFragment extends Fragment { public HolderFragment() { setRetainInstance(true); } …
39. How does it actually work? String HOLDER_TAG = "android.arch.lifecycle.state.StateProviderH olderFragment";
40. How does it know the activity is finishing?
41. How does it actually work? @Override public void onDestroy() { super.onDestroy(); mViewModelStore.clear(); }
42. Can I do it differently? ViewModel is not life cycle aware?
43. It just refuses to die
44. remember Never hold View or Activity references in the ViewModel!
45. What if Two Fragments of same Activity ask for same ViewModel.class via ViewModelProviders .of(this) .get(MyViewModel::class.java)
46. result Different ViewModels
47. What if Two Fragments of same Activity ask for same ViewModel.class via ViewModelProviders .of(this) .get(MyViewModel::class.java)
48. result •Fragment and Activity share the same FragmentManager •But implementation uses Activity’s FragmentManager but ChildFragmentManager for Fragments
49. result •Fragment and Activity share the same FragmentManager •But implementation uses Activity’s FragmentManager but ChildFragmentManager for Fragments
50. What if Two Fragments of same Activity ask for same ViewModel.class via ViewModelProviders .of(getActivity()) .get(MyViewMode::class).java
51. result Same ViewModel
52. Other uses cases communication layer between activities and fragments or fragments and fragments
53. So what about this LIFE CYCLE THING?
54. LIFECYCLE is a class that holds the information about the lifecycle state of a component
55. LIFECYCLE OWNER is a single method interface that denotes that the class has a Lifecycle. Fragments and Activities in Support Library 26.1.0+ already implement
56. LIFECYCLE OBSERVER class MyListener() : LifecycleObserver { @OnLifecycleEvent(Event.ON_START) fun onStart() { … }
57. LIFECYCLE OBSERVER activity.lifecycle.addObserver(listener)
58. LIFECYCLE OBSERVER activity.lifecycle.addObserver(listener) An observer added with a Lifecycle will be automatically removed if the corresponding Lifecycle moves to Lifecycle.State#DESTROYED state.
59. So SHOULD VIEWMODEL IMPLEMENT LIFE CYCLE OBSERVER?
60. NOOOOOOOOOOOO
61. ViewMODEL lives LOngER! Activity Activity ViewModel
62. IntroduciNG LIVE DATA Activity Activity LiveData LiveData ViewModel
63. IntroduciNG LIVE DATA •Observable similar to RxJava •Life cycle aware •Doesn’t emit when not needed •Memory leaks save
64. IntroduciNG LIVE DATA myModel.message.observe( this, Observer { display(it) })
65. What if I USE Rx Java?
66. Rx Java FULL PICTURE Activity ViewModel (un)subscribe
67. Rx Java FULL PICTURE Activity ViewModel Life cycle aware class (un)subscribe (un)subscribe
68. What if I USE DATA BINDING?
69. Data binding full picture XML ViewModel bind
70. Data binding full picture XML Activity ViewModel (un)bind bind Life cycle aware class (un)bind
71. 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
72. OR DON’T USE ARCH COMP VIEWMODEL Activity Life cycle ware ViewModel Repository Activity Life cycle ware ViewModel
73. let`s sum up •Well designed API •Goal: common architecture language •Use the parts you need •Know about life cycle •In beta
74. 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
75. Southpark copyright Disclaimer
76. viacom.tech
77. View Model and FRIENDS @PreusslerBerlin