Navigation patterns on Android and something new

Talk given @ AndroidDevConference in 2017 where I speak about navigation patterns on Android Apps.

Refs:

Conductor
https://github.com/bluelinelabs/Conductor
https://www.youtube.com/watch?v=0XSf7sX2rCQ (second talk)
https://github.com/artem-zinnatullin/TheContext-Podcast/blob/master/show_notes/Episode_13.md

Coordinators
https://www.youtube.com/watch?v=a1g3k3NObkE
http://khanlou.com/2015/01/the-coordinator/
http://khanlou.com/2015/10/coordinators-redux/

Transcript

1. Navigation Patterns on Android and something new !
2. Matheus C. Candido Android Developer @ Concrete Former Android @ iOasys @mcassiano @mcassiano
4. "
5. Activity responsibilities • Entry point for your app • UI building block • Navigation
6. • Usually done using Intents • Composed of tasks • Tasks have launch modes • Backstack control is messy • Activities know too much Navigation
8. …
9. It would be nice to have a little more control over the back stack
10. Then comes in something we know and love (hate?): Fragments
11. Fragments •Supposed to be a smaller Activity •They have their Own Lifecycle •Have their own back stack management
12. Own Lifecycle #
13. • Transactions are asynchronous • Sometimes this yields a bunch of IllegalStateExceptions • Enters commitNow() • BUT you can’t add transactions to the back stack: might break the order of async transactions Fragment trouble
14. • The Android OS can kill any activity in our process to free up memory • To make this transparent to the user, it gives us onSaveInstanceState() and saves state into a Bundle • If commit() and onSaveInstanceState() are called at the same time: $ • That transaction won’t be remembered as it was never recorded as part of the Activity IllegalStateExceptions
17. • Favoring ViewGroups • Simple Stack (Zhuinden) • Conductor (BlueLines) • Scoop (Lyft) • Flow (Square) & Mortar (sort of dead?) • Pancakes (Matt Logan) • Magellan (Wealthfront) Fragment alternatives Newish trend: single activity apps. Jake Wharton/Square started doing this way back though.
18. • Rewrite of the whole Fragment whole thing. Most of their components map to something Fragments offer • Controller -> Fragment • Router -> FragmentManager • ControllerTransaction -> FragmentTransaction • ControllerChangeHandler -> Describes animation in and out of Controllers Conductor
19. • Simple lifecycle • Only implementation (that I know of) that receives onActivityResult, onRequestPermissionResult, etc callbacks • popCurrentController(), popController(), pushController(), replaceTopController(), popToRoot() and the list goes on Conductor
20. router.pushController(RouterTransaction.with(new HomeController()) .pushChangeHandler(new FadeChangeHandler())
 .popChangeHandler(new FadeChangeHandler()));
21. router.pushController(RouterTransaction.with(...)
 .pushChangeHandler(new ArcFadeMoveChangeHandler(…))
 .popChangeHandler(new ArcFadeMoveChangeHandler(…));
22. router.popController(this);
23. List<RouterTransaction> newBackstack = Arrays.asList(
 RouterTransaction.with(newController1),
 RouterTransaction.with(newController2)
 );
 
 router.setBackstack(newBackstack, controllerChangeHandler);
24. • Encapsulation/Decoupling • Beautiful transitions on lower APIs • Transactions are executed synchronously • The equivalent implementation of a FragmentTransaction is Parcelable so it saves its state Advantages adopting this path
25. Pretty cool, this solves everything…
26. Pretty cool, this solves everything… not so fast. %
27. Views still do navigation.
28. Enters the Coordinator. &
29. • Also known as Directors or Application Controllers (as described in Patterns of Enterprise Application Architecture by Fowler) • Implemented successfully for iOS by Soroush Khanlou and is buzzing right now • It can be a simple POJO Coordinator
30. SignUpCoordinator
31. SignUpCoordinator AppCoordinator AuthenticationCoordinator LoggedInCoordinator WithdrawCoordinator CreditCardsCoordinator …
32. • Can be used to hold user input/data during flows (e.g.: registration flows, photo upload, multiple step flows w/ user input in general) • Allow easy reuse of entire flows inside of your application (I have actually implemented this in production and it works!) Coordinator
33. • In iOS the main requirement to implement this pattern is the NavigationController • A navigation controller object manages the currently displayed screens using the navigation stack, which is represented by an array of view controllers. Coordinator
34. So the only thing we need for this to work is access to the back stack!
 '
35. public interface Coordinator {
 
 void start();
 
 void setDetachListener(CoordinatorDetachListener listener);
 }
 public interface CoordinatorDetachListener {
 
 void onDetached(Coordinator coordinator);
 }
 public interface BaseCoordinatorListener {
 
 void controllerPopped(Controller controller);
 
 }
36. public class AppCoordinator implements CoordinatorDetachListener {
 
 private final Router router;
 private HomeCoordinator homeCoordinator;
 
 public AppCoordinator(Router router) {
 this.router = router;
 }
 
 public void start() {
 homeCoordinator = new HomeCoordinator(router);
 homeCoordinator.setDetachListener(this);
 homeCoordinator.start();
 }
 
 
 @Override
 public void onDetached(Coordinator coordinator) {
 homeCoordinator = null;
 }
 }

37. public class AppCoordinator implements CoordinatorDetachListener {
 
 private final Router router;
 private HomeCoordinator homeCoordinator;
 
 public AppCoordinator(Router router) {
 this.router = router;
 }
 
 public void start() {
 homeCoordinator = new HomeCoordinator(router);
 homeCoordinator.setDetachListener(this);
 homeCoordinator.start();
 }
 
 
 @Override
 public void onDetached(Coordinator coordinator) {
 homeCoordinator = null;
 }
 }

38. public class AppCoordinator implements CoordinatorDetachListener {
 
 private final Router router;
 private HomeCoordinator homeCoordinator;
 
 public AppCoordinator(Router router) {
 this.router = router;
 }
 
 public void start() {
 homeCoordinator = new HomeCoordinator(router);
 homeCoordinator.setDetachListener(this);
 homeCoordinator.start();
 }
 
 
 @Override
 public void onDetached(Coordinator coordinator) {
 homeCoordinator = null;
 }
 }

39. public class HomeCoordinator implements Coordinator, HomeNavListener, … {
 
 private final Router router;
 private CoordinatorDetachListener detachListener;
 
 public HomeCoordinator(Router router) {…}
 
 @Override
 public void start() {…}
 
 @Override
 public void setDetachListener(CoordinatorDetachListener listener) {…}
 
 @Override
 public void onNavigationClicked() {…}
 
 @Override
 public void onTransitionsClicked(Controller fromController) {…}
 
 @Override
 public void controllerPopped(Controller controller) {…}
 
 }

40. public class HomeCoordinator implements Coordinator, HomeNavListener,… {
 
 private final Router router;
 private CoordinatorDetachListener detachListener;
 
 public HomeCoordinator(Router router) {…}
 
 @Override
 public void start() {
 HomeController homeController = new HomeController();
 homeController.homeListener = this;
 homeController.baseCoordinatorListener = this;
 router.setRoot(RouterTransaction.with(homeController));
 }
 
 @Override
 public void setDetachListener(CoordinatorDetachListener listener) {…} ...

41. public class HomeCoordinator implements Coordinator, HomeNavListener,… {
 
 private final Router router;
 private CoordinatorDetachListener detachListener;
 
 public HomeCoordinator(Router router) {…}
 
 @Override
 public void start() {
 HomeController homeController = new HomeController();
 homeController.homeListener = this;
 homeController.baseCoordinatorListener = this;
 router.setRoot(RouterTransaction.with(homeController));
 }
 
 @Override
 public void setDetachListener(CoordinatorDetachListener listener) {…} ...

42. public class HomeController extends SomeBaseController {
 
 HomeNavListener homeListener;
 
 public HomeController() {}
 
 @NonNull
 @Override
 protected View inflateView(@NonNull LayoutInflater inflater, @NonNull ViewGroup container) {
 return inflater.inflate(R.layout.controller_home, container, false);
 }
 
 @Override
 protected void onViewBound(@NonNull View view) {
 super.onViewBound(view);
 
 ...
 } void onModelRowClick(Model model, int position) {…}
 ...
 
 }
43. public interface HomeNavListener {
 
 void onNavigationClicked();
 
 void onTransitionsClicked(Controller from); ...
 
 }
44. void onModelRowClick(Model m, int position) { switch (model) {
 case NAVIGATION:
 homeListener.onNavigationClicked();
 break;
 case TRANSITIONS:
 homeListener.onTransitionsClicked(this);
 break; ... } }
45. public class HomeCoordinator implements Coordinator, HomeNavListener, BaseCoordinatorListener {
 
 private final Router router;
 private CoordinatorDetachListener detachListener;
 
 public HomeCoordinator(Router router) {…}
 
 @Override
 public void start() {…}
 
 @Override
 public void setDetachListener(CoordinatorDetachListener listener) {…}
 
 @Override
 public void onNavigationClicked() {…}
 
 @Override
 public void onTransitionsClicked(Controller fromController) { router.pushController(TransitionDemoController .getRouterTransaction(0, fromController)); }
 
 @Override
 public void controllerPopped(Controller controller) {…}
 
 }
46. public abstract class SomeBaseController extends Controller { ... 
 @Override
 public void onDestroy() { if (baseCoordinatorListener != null) baseCoordinatorListener.controllerPopped(this);
 super.onDestroy();
 }
 }

47. public abstract class SomeBaseController extends Controller { ... 
 @Override
 public void onDestroy() { if (baseCoordinatorListener != null) baseCoordinatorListener.controllerPopped(this);
 super.onDestroy();
 }
 }

48. public class HomeCoordinator implements Coordinator, HomeNavListener, BaseCoordinatorListener {
 
 private final Router router;
 private CoordinatorDetachListener detachListener;
 
 public HomeCoordinator(Router router) {…}
 
 @Override
 public void start() {…}
 
 @Override
 public void setDetachListener(CoordinatorDetachListener listener) {…}
 
 @Override
 public void onNavigationClicked() {…}
 
 @Override
 public void onTransitionsClicked(Controller fromController) {…}
 
 @Override
 public void controllerPopped(Controller controller) { if (controller instanceof HomeController) { // let’s pretend it might not be null
 detachListener.onDetached(this);
 } }
 }
49. public class AppCoordinator implements CoordinatorDetachListener {
 
 private final Router router;
 private HomeCoordinator homeCoordinator;
 
 public AppCoordinator(Router router) {
 this.router = router;
 }
 
 public void start() {
 homeCoordinator = new HomeCoordinator(router);
 homeCoordinator.setDetachListener(this);
 homeCoordinator.start();
 }
 
 
 @Override
 public void onDetached(Coordinator coordinator) {
 homeCoordinator = null;
 }
 }

50. public class AppCoordinator implements CoordinatorDetachListener {
 
 private final Router router;
 private HomeCoordinator homeCoordinator;
 
 public AppCoordinator(Router router) {
 this.router = router;
 }
 
 public void start() {
 homeCoordinator = new HomeCoordinator(router);
 homeCoordinator.setDetachListener(this);
 homeCoordinator.start();
 }
 
 
 @Override
 public void onDetached(Coordinator coordinator) {
 homeCoordinator = null;
 }
 }

51. • Isolates navigation from view layer • Whole flows reusability • Makes controllers reusable in multiple flows • Multi-step forms is a breeze to implement • Can be used in only some parts of your app! • Testing is easier Overview
52. • Could not find a way to properly survive Process Death (configuration change is ok) • On boarding new users (not a trivial and widely adopted pattern, especially on Android) • Memory Management: can lead to memory leaks if not handled carefully. Clean up after your coordinators. • You *might* end up with a huge Coordinator (happened with me with a flow of more than 13 screens) Problems
53. •Use dependency injection • Don’t make your views see the coordinator directly, always make them pass through listeners (one method for each navigation action) • Use the coordinator for data mutation and views for fetching Recommendations
54. github.com/mcassiano sample app and other goodies
55. thank you!
56. ()
 thank you!