ThirtyInch - Living next to the Activity

Explains when you should use ThirtyInch and when you should use MVP at all. It also covers the different kinds of MVP, statless and stateful.
The code sample focuses on MVVM, or as I call it VPVM (view presenter viewmodel).

Project on github: https://github.com/grandcentrix/ThirtyInch
Sample on github: https://github.com/passsy/thirtyinch-sample

Transcript

1. ThirtyInch
   Living next to the Activity
   Pascal Welsch
   @passsy
   

   View Slide

2. Why is MVP a thing on Android?
   Moving all logic to a Presenter makes the code testable
   ○ Only self written code
   ○ Easy lifecycle, view attached/detached
   ○ Unit tests on JVM
   Activities and Fragments are hard to test
   ○ Have final methods and classes
   ○ Constructor dependency injection not possible
   ○ Requires emulator to run androidTest tests (slow)
   ○ The lifecycle is hard to mock and too complex
   

   View Slide

3. “What if I don’t write tests?”
   You should write tests!
   

   View Slide

4. “What if I really don’t write tests?”
   ● MVP introduces new boilerplate code
   ● There are some parts which will be more complex than before
   ● You most likely will not benefit from MVP
   Try testing with MVP, it will be easier than ever before!
   Don’t use MVP
   

   View Slide

5. MVP != MVP
   Stateless
   Presenter will be created every time in
   Activity#onCreate
   Doesn’t solve the problem or network requests
   when the phone is changing orientation
   Hold state (model) in the Activity and save is
   in onSaveInstanceState()
   Stateful
   Presenter survives orientation changes
   Network requests keep running when the phone
   is changing orientation
   Hold state objects (model) in the Presenter
   

   View Slide

6. Stateless Presenter
   ● Created in onCreate()
   ● View attached in constructor
   ● New Presenter object when the
   Activity recreates
   ● Move state to new Activity
   instance with
   onSaveInstanceState()
   

   View Slide

7. Stateless Presenter
   ● Created in onCreate()
   ● View attached when displayed
   ● View detached when the app in
   in background
   ● New Presenter object when the
   Activity recreates
   ● Move state to new Activity
   instance with
   onSaveInstanceState()
   

   View Slide

8. If you build MVP with a
   stateless Presenter
   you don’t need a library
   

   View Slide

9. Stateful Presenter
   Created in onCreate() when
   savedInstanceState == null
   Destroy callback when Activity gets
   finished in onDestroy() with
   isFinishing() == true
   When the Activity gets recreated
   the Presenter does survives!
   

   View Slide

10. Stateful Presenter
    The state (model) of the Activity can be saved in
    the Presenter (in memory) instead of using
    Parcelables
    Ignores all lifecycle events except for the availability of
    the View
    Network requests can run during a orientation change
    and update the model, not the view
    Implementing a stateful Presenter works best with a
    ViewModel and a passive view (VPVM)
    Living next
    to the
    Activity
    

    View Slide

11. ThirtyInch supports both types
    public MyStatelessPresenter() {
    super(new TiConfiguration.Builder()
    .setRetainPresenterEnabled(false)
    .build());
    }
    Stateless Stateful (default)
    

    View Slide

12. Sample with
    ViewModel
    github.com/passsy/thirtyinch-sample
    

    View Slide

13. View Slide

14. 5 small steps to
    attach a Presenter to
    your Activity
    

    View Slide

15. 1. Define View interface
    interface EditTaskView extends TiView {
    void setTitle(String title);
    void showLoadingIndicator(boolean show);
    }
    

    View Slide

16. 2. Create Activity
    public class EditTaskActivity
    extends TiActivity
    implements EditTaskView {
    

    View Slide

17. 3. Activity#providePresenter()
    public class EditTaskActivity
    extends TiActivity
    implements EditTaskView {
    @NonNull @Override
    public AddEditTaskPresenter providePresenter() {
    final String taskId =
    getIntent().getStringExtra(EditTaskActivity.ARGUMENT_EDIT_TASK_ID);
    final TasksRepository tasksRepository = Injection.provideTasksRepository(this);
    return new EditTaskPresenter(taskId, tasksRepository);
    }
    

    View Slide

18. 4. Activity implements EditTaskView
    @Override public void setTitle(String title) {
    mTitle.setText(title);
    }
    @Override public void showLoadingIndicator(final boolean show) {
    if (show) {
    mLoadingIndicator.show();
    } else {
    mLoadingIndicator.hide();
    }
    }
    

    View Slide

19. 5. send UI input events
    public class EditTaskActivity
    extends TiActivity
    implements EditTaskView {
    @Override protected void onCreate(final Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.addtask_act);
    mFab = (FloatingActionButton) findViewById(R.id.fab_edit_task_done);
    mFab.setOnClickListener(view -> {
    getPresenter().saveTask();
    });
    

    View Slide

20. Write the Presenter
    

    View Slide

21. View Slide

22. Presenter constructor
    class EditTaskPresenter extends TiPresenter {
    EditTaskPresenter(@Nullable String taskId,
    @NonNull TasksDataSource tasksRepository) {
    mTaskId = taskId;
    mTasksRepository = checkNotNull(tasksRepository);
    mViewModel = new EditTaskViewModel();
    }
    

    View Slide

23. Presenter#onCreate()
    @Override
    protected void onCreate() {
    super.onCreate();
    mViewModel.setLoadingTask(true);
    mRepositoryRequest = mTasksRepository.getTask(mTaskId, task -> {
    mViewModel.setLoadingTask(false);
    mViewModel.setTask(task);
    });
    }
    

    View Slide

24. View Slide

25. Presenter#onAttachView(view)
    @Override
    protected void onAttachView(@NonNull final EditTaskView view) {
    super.onAttachView(view);
    mViewModel.setOnChangeListener(model -> {
    view.setTitle(model.getTitle());
    view.showLoadingIndicator(model.isLoading());
    });
    }
    

    View Slide

26. ViewModel properties
    class EditTaskViewModel {
    private Task mTask = null;
    private boolean mIsLoadingTask = false;
    private NotifyChangeListener mNotifyChangeListener;
    private void notifyChange() {
    if (mNotifyChangeListener != null) {
    mNotifyChangeListener.onChange(this);
    }
    }
    ...
    

    View Slide

27. ViewModel notifyChange()
    class EditTaskViewModel {
    ...
    public boolean isLoading() {
    return mIsLoadingTask;
    }
    public void setLoadingTask(final boolean loadingTask) {
    if (mIsLoadingTask != loadingTask) {
    mIsLoadingTask = loadingTask;
    notifyChange();
    }
    }
    

    View Slide

28. ViewModel is
    the truth
    Update the ViewModel (not view) when
    - data changes
    - receiving UI events
    Update the View when
    - the View attaches
    - The ViewModel changes
    This prevents NPEs when View == null
    (detached)
    Always update everything (React way)
    

    View Slide

29. Mutating UI state
    is error-prone,
    always update
    everything
    

    View Slide

30. DistinctUntilChanged
    mViewModel.setOnChangeListener(model -> {
    view.setTitle(model.getTitle());
    view.showLoadingIndicator(model.isLoading());
    });
    interface EditTaskView extends TiView {
    @DistinctUntilChanged
    void showLoadingIndicator(boolean show);
    }
    @DistinctUntilChanged
    Prevents calling methods with
    the same arguments over and
    over again
    

    View Slide

31. View Slide

32. Presenter#onDetachView()
    @Override
    protected void onDetachView() {
    super.onDetachView();
    mViewModel.setOnChangeListener(null);
    }
    

    View Slide

33. Presenter#onDetachView()
    @Override
    protected void onDestroy() {
    super.onDestroy();
    if (!mRepositoryRequest.isCanceled()) {
    mRepositoryRequest.cancel();
    }
    }
    

    View Slide

34. Modules
    def tiVersion = '0.8.0-rc1'
    compile "net.grandcentrix.thirtyinch:thirtyinch:$tiVersion"
    // rx extension
    compile "net.grandcentrix.thirtyinch:thirtyinch-rx:$tiVersion"
    // test extension
    testCompile "net.grandcentrix.thirtyinch:thirtyinch-test:$tiVersion"
    

    View Slide

35. Run unit tests
    on the JVM
    

    View Slide

36. Testing on JVM
    @Test
    public void populateTask_callsRepoAndUpdatesView() {
    // Get a reference to the class under test
    final EditTaskPresenter presenter =
    new EditTaskPresenter("1", mTasksRepository);
    final TiPresenterInstructor instructor =
    new TiPresenterInstructor<>(presenter);
    // When task is requested and view is attached
    final AddEditTaskView view = mock(AddEditTaskView.class);
    instructor.attachView(view);
    

    View Slide

37. Testing
    // When task is requested and view is attached
    final AddEditTaskView view = mock(AddEditTaskView.class);
    instructor.attachView(view);
    verify(view).setTitle("");
    verify(view).showLoadingIndicator(true);
    

    View Slide

38. // get fake task from repository
    final ArgumentCaptor captor =
    ArgumentCaptor.forClass(TasksDataSource.GetTaskCallback.class);
    verify(mTasksRepository).getTask(eq("1"), captor.capture());
    // Simulate callback
    final Task testTask = new Task("TITLE", "DESCRIPTION");
    captor.getValue().onTaskLoaded(testTask);
    // Then the task repository is queried and the view updated
    verify(view).showLoadingIndicator(false);
    verify(view, atLeastOnce()).setTitle(testTask.getTitle());
    }
    

    View Slide

39. Why you should use ThirtyInch
    ● most likely better tested than your homemade one;
    Stateless or stateful
    ● Grown and stabilized over the last 1.5 years in
    multiple projects
    ● Gives you a stateful Presenter for Activities and
    Fragments which survives configuration changes
    Try it now!
    

    View Slide

40. github.com/grandcentrix/ThirtyInch
    Pascal Welsch
    @passsy
    grandcentrix.net
    @grandcentrix
    

    View Slide