Dynamic Navigation in Modularized Apps

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September 27, 2021 Dynamic Navigation in Modularized Apps 1

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about me Github: https://github.com/sumayyah LinkedIn: https://www.linkedin.com/in/sumayyah-ahmed 2

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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

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How does modularization make navigation complicated? 4

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A B 5

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A B startActivity() supportFragmentManager.beginTransaction() 6

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A B findNavController().navigate( some id for B ) 7

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A B findNavController().navigate( some id for B ) 8

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A B findNavController().navigate(??) 9

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Host app Library A Library B Library C 10

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Host app Library A Library B Library C ?? ?? 11

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Host app Library A Host Activity Feature Activity startActivity(this, FeatureActivity::class.java) 12

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What if you can’t do a handoff? 13

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Host app Library A Host Activity Feature Activity ?? 14

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Host app Library A Host Activity Feature Activity Fragment A Fragment B Fragment C Graph ?? 15

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Navigation is dynamic 16

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Problem 1: navigating between libraries with known destinations Problem 2: navigating between libraries with unknown destinations 17

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Problem 1: navigating between libraries with known destinations 18

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Compile time solution: deep links 19

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Library 20 library_nav

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Library Host app 21 library_nav

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Library Host app 22 library_nav

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Library Host app 23 library_nav

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Library Host app 24 in code: library_nav

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how does this work? 25

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navigate(destination: NavDestination) 26

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NavController Nav Graph All the destinations Adds and removes destinations onto and off the backstack 27

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XML NavController::class.java mNavGraph SparseArray NavGraph::class.java 28

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FragmentClass::class.java Navigator Actions Deep link NavDestination XML Created by NavComponents Navigator uses FragmentTransaction Navigator uses Intents 29

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NavDestination Navigator Knows how to navigate to this navGraph 31

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NavDestination Navigator 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.navigate() 4. Navigator adds deep linked destination fragment to backstack 32

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Library Host app 33 library_nav

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How can we ensure that users always see a cohesive flow? 34

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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

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Fragment A from host app ?? – Fragment D Fragment C from host app How can we share data across a backstack? 36

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NavGraphViewModels 37

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SavedStateHandle 38

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NavBackStackEntry NavBackStackEntry NavBackStackEntry NavController SavedStateHandle ViewModelStore NavDestination Fragment Backstack 39

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Fragment A Fragment C navController.currentBackstackEntry.savedStateHandle.set[“hasSeenNewOnboardingFlow”, false] 41

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Fragment A Fragment D Fragment C navController.previousBackstackEntry.savedStateHandle.set[“hasSeenNewOnboardingFlow”, true] 42

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Fragment A Fragment C navController.currentBackstackEntry.savedStateHandle.get(“hasSeenNewOnboardingFlow”) 43

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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

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Problem 2: navigating between libraries with unknown destinations 45

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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

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Fragment A Fragment C Fragment D Fragment E ?? 47

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Runtime solution: addDestination 48

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how does this work? 50

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Fragment A Fragment B Fragment C Fragment E NavDestination Fragment D External lib 51

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52 Summary Navigation doesn’t have to be statically defined! Modularization creates unknowns and dynamically handled navigation can help deal with these unknowns