Dynamic Navigation in Modularized Apps

Transcript

1. September 27, 2021 Dynamic Navigation in Modularized Apps 1
2. about me Github: https://github.com/sumayyah LinkedIn: https://www.linkedin.com/in/sumayyah-ahmed 2
3. Overview 30 min talk, then questions How does modularization make Navigation Components complicated? How can we solve those problems? How can we ensure that users always see a cohesive flow? 3
4. How does modularization make navigation complicated? 4
5. A B 5
6. A B startActivity() supportFragmentManager.beginTransaction() 6
7. A B findNavController().navigate( some id for B ) 7
8. A B findNavController().navigate( some id for B ) 8
9. A B findNavController().navigate(??) 9
10. Host app Library A Library B Library C 10
11. Host app Library A Library B Library C ?? ?? 11
12. Host app Library A Host Activity Feature Activity startActivity(this, FeatureActivity::class.java) 12
13. What if you can’t do a handoff? 13
14. Host app Library A Host Activity Feature Activity ?? 14
15. Host app Library A Host Activity Feature Activity Fragment A Fragment B Fragment C Graph ?? 15
16. Navigation is dynamic 16
17. Problem 1: navigating between libraries with known destinations Problem 2: navigating between libraries with unknown destinations 17
18. Problem 1: navigating between libraries with known destinations 18
19. Compile time solution: deep links 19
20. Library 20 library_nav
21. Library Host app 21 library_nav
22. Library Host app 22 library_nav
23. Library Host app 23 library_nav
24. Library Host app 24 in code: library_nav
25. how does this work? 25
26. navigate(destination: NavDestination) 26
27. NavController Nav Graph All the destinations Adds and removes destinations onto and off the backstack 27
28. XML <fragment> <activity> <include> NavController::class.java mNavGraph SparseArray<NavDestination> NavGraph::class.java 28
29. FragmentClass::class.java Navigator<T> Actions Deep link NavDestination XML Created by NavComponents Navigator<Fragment> uses FragmentTransaction Navigator<Activity> uses Intents 29
31. NavDestination Navigator<NavGraph> Knows how to navigate to this navGraph 31
32. NavDestination Navigator<NavGraph> Knows how to navigate to this navGraph 1. Iterate through NavDestinations to find a deep link match 2. NavGraph destination knows about its own deep links 3. NavController delegates navigation to Navigator<NavGraph>.navigate() 4. Navigator adds deep linked destination fragment to backstack 32
33. Library Host app 33 library_nav
34. How can we ensure that users always see a cohesive flow? 34
35. How do fragments in the stack react to this unknown destination? Fragment A from host app ?? – Fragment D Fragment C from host app What if Fragment C needs to know what happens in Fragment D? They don’t share a ViewModel or Activity or data store 35
36. Fragment A from host app ?? – Fragment D Fragment C from host app How can we share data across a backstack? 36
37. NavGraphViewModels 37
38. SavedStateHandle 38
39. NavBackStackEntry NavBackStackEntry NavBackStackEntry NavController SavedStateHandle ViewModelStore NavDestination Fragment Backstack 39
41. Fragment A Fragment C navController.currentBackstackEntry.savedStateHandle.set[“hasSeenNewOnboardingFlow”, false] 41
42. Fragment A Fragment D Fragment C navController.previousBackstackEntry.savedStateHandle.set[“hasSeenNewOnboardingFlow”, true] 42
43. Fragment A Fragment C navController.currentBackstackEntry.savedStateHandle.get(“hasSeenNewOnboardingFlow”) 43
44. the problem with SavedStateHandle It’s a little hacky! It requires fragments to know in advance what data is saved and in what format It’s fragile 44
45. Problem 2: navigating between libraries with unknown destinations 45
46. what if you don’t know where to go till runtime? For example: A nav destination relies on external library for content Fragment A ?? Fragment C External lib 46
47. Fragment A Fragment C Fragment D Fragment E ?? 47
48. Runtime solution: addDestination 48
50. how does this work? 50
51. Fragment A Fragment B Fragment C Fragment E NavDestination Fragment D External lib 51
52. 52 Summary Navigation doesn’t have to be statically defined! Modularization creates unknowns and dynamically handled navigation can help deal with these unknowns