Android architecture components
- 1. Architecture Components + Diego Nascimento Software Engineer at CESAR
- 2. What are the goals of these "architecture components" ?
- 3. Architecture Components - API - Room - ViewModel - LiveData - Lifecycle
- 4. * Taken from the book O'Reilly Head First "Design Patterns" The one who is listening is Observer... And the other one, who is emitting events, is subject or observable.
- 5. LiveData public LiveData<Films> getFilms() { final MutableLiveData<Films> data = new MutableLiveData<>(); webService.getFilms().enqueue(new Callback<Films>() { @Override public void onResponse(Call<Films> call, Response<Films> response) { data.setValue(response.body()); } }); return data; } // Update the list when the data changes viewModel.getFilms().observe(this, new Observer<Films>() { @Override public void onChanged(@Nullable Films films) { if (films != null) { lstFilms.setAdapter(new FilmsAdapter(getApplicationContext(), films.results); } });
- 6. Configuration Change onCreate onStart onResume onPause onStop onDestroy onStart onResume onCreate Activity Created Activity Rotated onCleared ViewModel Scope
- 7. ViewModel The ViewModel class is designed to store and manage UI-related data so that the data survives configuration changes such as screen rotations. public class MyViewModel extends ViewModel { private MutableLiveData<List<User>> users; public LiveData<List<User>> getUsers() { if (users == null) { users = new MutableLiveData<List<Users>>(); loadUsers(); } return users; } private void loadUsers() { // do async operation to fetch users } } public void onCreate(Bundle savedInstanceState) { MyViewModel model = ViewModelProviders.of(this).get(MyViewModel.class); model.getUsers().observe(this, users -> { // update UI }); }
- 8. Handling Lifecycle The android.arch.lifecycle package provides classes and interfaces that let you build lifecycle-aware components — which are components that can automatically adjust their behavior based on the current lifecycle of an activity or fragment
- 9. LifecycleOwner LifecycleOwner is a single method interface that denotes that the class has a Lifecycle. It has one method, getLifecycle(), which must be implemented by the class. public class MyFragment extends Fragment implements LifecycleRegistryOwner { LifecycleRegistry lifecycleRegistry = new LifecycleRegistry(this); @Override public LifecycleRegistry getLifecycle() { return lifecycleRegistry; } }
- 10. LifecycleObserver LifecycleObserver observe LifecycleOwners, and are notified of lifecycle changes. public class MyObserver implements LifecycleObserver { @OnLifecycleEvent(Lifecycle.Event.ON_RESUME) public void onResume() { } @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE) public void onPause() { } } aLifecycleOwner.getLifecycle().addObserver(new MyObserver());