Model View Presenter: The Life-Changing Magic of Tidying Up Your Presentation Layer

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1. Model View Presenter The Life-Changing Magic of Tidying Up Your Presentation Layer Yun Cheng ASICS Digital
4. My coworkers Me
7. • Problems to Solve ◦ Separation of Concerns ◦ Unit Testing • What is Model View Presenter? • Steps to refactor to MVP • Pros/Cons Overview
8. It is a common mistake to write all your code in an Activity or a Fragment. Any code that does not handle a UI or operating system interaction should not be in these classes. Keeping them as lean as possible will allow you to avoid many lifecycle related problems. --Android Developers Guide https://developer.android.com/jetpack/docs/guide Separation of Concerns
9. Why should we unit test? • Fast to run • No Robolectric or Espresso • Foundation for working UI logic Why is unit testing hard in Android? • Android life cycle • Lots of dependencies Unit Testing
10. public class DateUtil { DateUtil() { // Constructor } public int getPreviousCalendarDay(int day) { return ((day + 5) % 7) + 1; } } Normal Java Code
11. @Test public void previousDayTest() { DateUtil dateUtil = DateUtil(); assertEquals(dateUtil.getPreviousCalendarDay(Calendar.MONDAY), Calendar.SUNDAY); } Normal Unit Testing
12. Android Unit Testing public class TripListActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(); methodIWantToTest(); } @Override protected void onResume() {} @Override protected void onDestroy() {} protected void methodIWantToTest() {} }
13. How did we solve these problems? • No separation of concern • Not testable Trip List Activity
14. Trip List Activity
15. Trip List Activity (BEFORE) • onCreate • onResume • onDestroy • onPause • onRefresh • onLowMemory • onSaveInstanceState • onActivityResult • setTripProgressObservable • triggerActivityPushSync • reloadTrips • syncDone • syncDoneWithError • LoadTripsTask • createAdapter • onTripsLoaded • setUpSwipeRefreshLayout • setLayout • showHideViewsOnSync • trackAnActivity • unregisterForBroadcasts • registerForBroadcasts • connectionError • getViewEventName • getTripCount • findIndexByTripUuid • startSyncTimer • completeSyncTimer
16. Trip List Activity (BEFORE) • onCreate • onResume • onDestroy • onPause • onRefresh • onLowMemory • onSaveInstanceState • onActivityResult • setTripProgressObservable • triggerActivityPushSync • reloadTrips • syncDone • syncDoneWithError • LoadTripsTask • createAdapter • onTripsLoaded • setUpSwipeRefreshLayout • setLayout • showHideViewsOnSync • trackAnActivity • unregisterForBroadcasts • registerForBroadcasts • connectionError • getViewEventName • getTripCount • findIndexByTripUuid • startSyncTimer • completeSyncTimer Lifecycle methods Networking methods View methods Broadcast methods Utility methods DB methods
17. Separation of Concerns Activity Lifecycle methods Presentation logic Views The data
18. Separation of Concerns Activity Lifecycle methods Presentation logic Views Model The data
19. Separation of Concerns Activity Lifecycle methods Presentation logic Model The data View Views
20. Model View Presenter Activity Lifecycle methods Model The data View Views Presenter Presentation logic
21. Model View Presenter Activity Lifecycle methods Model The data View Views Presenter Presentation logic ---------- Lifecycle
22. POJOS extends Activity/Fragment Model View Presenter Lifecycle Lifecycle methods Navigation Model The data View Views View logic Presenter Presentation logic
23. Androidy Model View Presenter Lifecycle Lifecycle methods Navigation Model The data View Views View logic Presenter Presentation logic Not Androidy
24. Model View Presenter Lifecycle Lifecycle methods Model The data View Views Presenter Presentation logic IView IPresenter ILifecycle
25. Contract Model View Presenter Lifecycle Lifecycle methods Model The data View Views Presenter Presentation logic IView IPresenter ILifecycle
26. Step 1: Split up the activity into model, view, presenter, lifecycle Step 2: Connect all the components Step 3: Create the presenter using a factory Step 4: Write unit tests How to Refactor to MVP
27. Presenter POJO presentation logic Step 1: Split up the activity View View View logic recyclerView tripHistoryAdapter Lifecycle Lifecycle methods Navigation Model tripList
28. Runkeeper Architecture Managers -TripManager -FriendsManager -CoachingManager -etc. WebClient Database Lifecycle Lifecycle methods Model The data View Views Presenter Presentati on logic APP ARCHITECTURE SCREEN ARCHITECTURE Business logic
29. Split up the Activity • TripListActivity • TripListModel • TripListView • TripListPresenter • TripListContract ◦ IActivity ◦ IModel ◦ IView ◦ IPresenter cmd+alt+b Goto Implementation Works on methods to find where they are implemented/overriden.
30. Activity @Override public void onActivityResult(int requestCode, int resultCode, Intent data) { final boolean deleted = data.getBooleanExtra(TRIP_DELETED, false); ... presenter.handleActivityResult(requestCode, resultCode, index, deleted); } Activity-Presenter Relationship Presenter public void handleActivityResult(int requestCode, int resultCode, boolean index, boolean deleted) { ... triggerActivityPushSync(); }
31. Presenter public void triggerActivityPushSync() { view.updateUIForSyncInProgress(); ... } Presenter-View Relationship View public void updateUIForSyncInProgress() { loadingAnimation.setVisibility(VISIBLE); swipeRefreshLayout.setVisibility(GONE); ... }
32. Trip List Activity (AFTER) • onCreate • createPresenter • onResume • onDestroy • onPause • onLowMemory • onSaveInstanceState • onActivityResult • getViewEventName • showConnectionErrorToast • trackAnActivity • createMapFactory • Lines of code ◦ 747 --> 132 • Number of methods ◦ 27 --> 12
33. Because our presenter is just a POJO, we can easily unit test our logic Key Takeaway Presenter POJO presentation logic ✓T
34. Step 2: Connect the components Lifecycle Lifecycle methods Model The data View Views Presenter Presentation logic
35. Lifecycle to Presenter Activity protected TripListContract.IPresenter presenter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); presenter = createPresenter(); } @Override public TripListContract.IActivity createPresenter() { //Create presenter here }
36. View to Presenter View protected TripListContract.IPresenter presenter; @Override public void bindPresenter(TripListContract.IPresenter presenter) { this.presenter = presenter; }
37. Presenter Presenter protected TripListPresenter(TripListContract.IView view, TripListContract.ILifecycle activity, TripListContract.IModel model, RKWebClient webClient, TripManager tripManager) { this.view = view; this.activity = activity; this.model = model; this.webClient = webClient; this.tripManager = tripManager; view.bindPresenter(this); } Inject all these dependencies
38. Step 3: Create the presenter using a factory (optional) Activity @Override public TripListContract.IActivity createPresenter() { //Create presenter here }
39. Dependency: any kind of object that our presenter class needs to do its job Dependency Injection Presenter public Observable<ArrayList<Trip>> getReloadTripsObservable() { TripManager tripManager = TripManager.openManager(context); return Observable.fromCallable(() -> { ... return tripManager.getLatestTrips(); } }
40. Remove tight coupling by injecting dependencies into the presenter’s constructor Dependency Injection Presenter public Observable<ArrayList<Trip>> getReloadTripsObservable() { TripManager tripManager = TripManager.openManager(context); return Observable.fromCallable(() -> { ... return tripManager.getLatestTrips(); } } Tightly coupled dependency
41. public class TripListPresenterFactory { @Override public TripListContract.IPresenter create(Context context, TripListContract.ILifecycle activity) { } } Presenter Factory Create all dependencies Return a new presenter, injecting in the dependencies
42. public class TripListPresenterFactory { @Override public TripListContract.IPresenter create(Context context, Intent intent, Bundle savedInstanceState, TripListContract.ILifecycle activity) { LayoutInflater layoutInflater = LayoutInflater.from(context); RKWebClient webClient = new RKWebClient(context); TripManager tripManager = TripManager.openTripManager(context); TripListContract.IModel model = new TripListModel(); TripHistoryAdapter adapter = new TripHistoryAdapter(model); TripListContract.IView view = new TripListView(layoutInflater, context); view.attachNewAdapter(adapter); return new TripListPresenter(view, activity, model, webClient, tripManager); } } Presenter Factory Create all dependencies Return a new presenter, injecting in the dependencies }
43. Step 4: Write unit tests
44. Unit Testing Tools
45. @Mock private TripListView mockView; @Mock private TripListActivity mockActivity; @Mock private TripListModel mockModel; @Mock private RKWebClient mockWebClient; @Mock private TripManager mockTripManager; @Mock private TripHistoryAdapter mockAdapter; Mock Dependencies
46. @Before public void setUp() { ... presenter = new TripListPresenter(mockView, mockActivity, mockModel, mockWebClient, mockTripManager); } Inject Dependencies
47. Example: Delete a Trip Tap to view details Back to Trip List Activity
48. Example: Delete a Trip Activity @Override public void onActivityResult(int requestCode, int resultCode, Intent data) { final boolean deleted = data.getBooleanExtra(TRIP_DELETED, false); ... presenter.handleActivityResult(requestCode, resultCode, index, deleted); } Presenter public void handleActivityResult(int requestCode, int resultCode, boolean index, boolean deleted) { ... if (deleted) { handleTripDeletedFromTripList(index); } }
49. @Test public void onActivityResultDeleted() throws Exception { int tripCountBefore = model.getTripCount(); //Set up the test so that tripDeleted is true boolean tripDeleted = true; //Call the method of interest presenter.handleActivityResult(requestCode, resultCode, index, tripDeleted); //Assert that list is 1 trip fewer int tripCountAfter = model.getTripCount(); assertEquals(tripCountAfter, tripCountBefore - 1); } Write Tests
50. @Test public void onActivityResultDeleted() throws Exception { int tripCountBefore = model.getTripCount(); //Set up the test so that tripDeleted is true boolean tripDeleted = true; //Call the method of interest presenter.handleActivityResult(requestCode, resultCode, index, tripDeleted); //Assert that list is 1 trip fewer int tripCountAfter = model.getTripCount(); assertEquals(tripCountAfter, tripCountBefore - 1); } Write Tests
51. @Test public void onActivityResultDeleted() throws Exception { int tripCountBefore = model.getTripCount(); //Set up the test so that tripDeleted is true boolean tripDeleted = true; //Call the method of interest presenter.handleActivityResult(requestCode, resultCode, index, tripDeleted); //Assert that list is 1 trip fewer int tripCountAfter = model.getTripCount(); assertEquals(tripCountAfter, tripCountBefore - 1); } Write Tests
52. @Test public void onActivityResultDeleted() throws Exception { int tripCountBefore = model.getTripCount(); //Set up the test so that tripDeleted is true boolean tripDeleted = true; //Call the method of interest presenter.onActivityResult(requestCode, resultCode, mockIntent); //Assert that list is 1 trip fewer int tripCountAfter = model.getTripCount(); assertEquals(tripCountAfter, tripCountBefore - 1); } Write Tests
53. Example: Swipe to Refresh View @Override public void onRefresh() { if (!presenter.getSyncInProgress()) { visibleItemPosition = 0; presenter.triggerActivityPushSync(); } } Presenter public void triggerActivityPushSync() { view.updateUIForSyncInProgress(); ... // Start syncing to server webClient.beginSync(); }
54. @Test public void showProgressDuringSync() throws Exception { //Set up the test doNothing().when(mockWebClient.beginSync()) //Call the method of interest presenter.triggerActivityPushSync(); //Assert that the progress bar is showing assertTrue(mockView.inProgress()); } Write Tests
55. @Test public void showProgressDuringSync() throws Exception { //Set up the test doNothing().when(mockWebClient.beginSync()) //Call the method of interest presenter.triggerActivityPushSync(); //Assert that the progress bar is showing assertTrue(mockView.inProgress()); } Write Tests
56. @Test public void showProgressDuringSync() throws Exception { //Set up the test doNothing().when(mockWebClient.beginSync()) //Call the method of interest presenter.triggerActivityPushSync(); //Assert that the progress bar is showing assertTrue(mockView.inProgress()); } Write Tests
57. How to Refactor to MVP
58. Step 1: Split up the activity into model, view, presenter, lifecycle Step 2: Connect all the components Step 3: Create the presenter using a factory Step 4: Write unit tests How to Refactor to MVP
59. Cons • Has many classes and interfaces • Must consider when the activity gets destroyed Pros and Cons Pros • Can now achieve separation of concerns • Can now test previously huge and untestable activities/fragments
60. Thanks!