Let the button do safe navigation

Explore behaviors of Jetpack Navigation Component.
Share some tips when doing navigation from a click event.

Transcript

1. Let the button do safe navigation Mao Yufeng
2. Self-Introduction Mao Yufeng • @myf_pa • https://github.com/lcdsmao • https://medium.com/@lcdsmao • CyberAgent/CATS
3. Ensure navigation is safe
4. Navigation Graph:
5. button_navigate_bar.setOnClickListener { findNavController().navigate(R.id.action_fooFragment_to_barFragment) } FooFragment.kt:
6. java.lang.IllegalArgumentException: navigation destination com.github.lcdsmao.uievent:id action_fooFragment_to_barFragment is unknown to this NavController at androidx.navigation.NavController.navigate(NavController.java:789) at androidx.navigation.NavController.navigate(NavController.java:730) at androidx.navigation.NavController.navigate(NavController.java:716) at androidx.navigation.NavController.navigate(NavController.java:704) at com.github.lcdsmao.uievent.FooFragment$onCreateView$$inlined$apply$lambda$1.onClick(FooFragment.kt:22) at android.view.View.performClick(View.java:6256) at android.view.View$PerformClick.run(View.java:24710) at android.os.Handler.handleCallback(Handler.java:789) at android.os.Handler.dispatchMessage(Handler.java:98) at android.os.Looper.loop(Looper.java:251) at android.app.ActivityThread.main(ActivityThread.java:6572) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767) This exception occurs when calling Action that does not belong to the current Fragment
7. <fragment android:id="@+id/fooFragment" android:name="com.github.lcdsmao.uievent.FooFragment" android:label="FooFragment"> <action android:id="@+id/action_fooFragment_to_barFragment" app:destination="@id/barFragment" /> </fragment> <fragment android:id="@+id/barFragment" android:name="com.github.lcdsmao.uievent.BarFragment" android:label="BarFragment" /> nav_main.xml:
8. <fragment android:id="@+id/fooFragment" android:name="com.github.lcdsmao.uievent.FooFragment" android:label="FooFragment"> <action android:id="@+id/action_fooFragment_to_barFragment" app:destination="@id/barFragment" /> </fragment> <fragment android:id="@+id/barFragment" android:name="com.github.lcdsmao.uievent.BarFragment" android:label="BarFragment" /> nav_main.xml:
9. button_navigate_bar.setOnClickListener { findNavController().navigate(R.id.action_fooFragment_to_barFragment) findNavController().navigate(R.id.action_fooFragment_to_barFragment) } FooFragment.kt:
10. NavController holds its own back stack of navigation info and check the state before each navigation private final Deque<NavBackStackEntry> mBackStack = new ArrayDeque<>(); NavController.java
11. button_navigate_bar.setOnClickListener { this@FooFragment.logv("Click NavigateBarMaybeCrash") this@FooFragment.logv("Before Call Navigate") findNavController().navigate(R.id.action_fooFragment_to_barFragment) this@FooFragment.logv("After Call Navigate") } V/FooFragment: Click NavigateBar V/FooFragment: Before Call Navigate V/FooFragment: After Call Navigate V/BarFragment: onAttach V/BarFragment: onCreate V/BarFragment: onViewCreated V/BarFragment: onActivityCreated V/BarFragment: onStart V/BarFragment: onResume V/FooFragment: onPause V/FooFragment: onStop V/FooFragment: onDestroyView FragmentTransaction will not be performed immediately FooFragment.kt: Pending input events are canceled at onStop
12. The View system is completely independent from any higher level framework such as Fragments or Navigation, so there's not much we can do. https://issuetracker.google.com/issues/136024230
13. button_navigate_bar.setOnClickListener { val navController = findNavController() navController.navigate(R.id.action_fooFragment_to_barFragment) } Check to see if we haven't already navigated away
14. button_navigate_bar.setOnClickListener { val navController = findNavController() if (navController.currentDestination?.id == R.id.fooFragment) { navController.navigate(R.id.action_fooFragment_to_barFragment) } } Check to see if we haven't already navigated away
15. fun NavController.safeNavigate( @IdRes currentId: Int, @IdRes destId: Int, ) { if (currentDestination?.id == currentId) { navigate(destId) } } NavigationExt.kt:
16. BaseFragment.kt: abstract class BaseFragment : Fragment() { @IdRes open val navId: Int = 0 protected fun navigate(@IdRes destId: Int) { require(navId != 0) { "Need fragment id in navGraph for safe navigation" } findNavController().safeNavigate(desId) } } class FooFragment : BaseFragment() { override val navId: Int = R.id.fooFragment override fun onViewCreated(view: View, savedInstanceState: Bundle?) { super.onViewCreated(view, savedInstanceState) button_navigate_bar.setOnClickListener { navigate(R.id.action_fooFragment_to_barFragment) } } } FooFragment.kt:
17. <fragment android:id="@+id/fooFragment" android:name="com.github.lcdsmao.uievent.FooFragment" android:label="FooFragment"> <action android:id="@+id/action_fooFragment_to_dialogFragment" app:destination="@id/dialogFragment" /> </fragment> <dialog android:id="@+id/dialogFragment" android:name="com.github.lcdsmao.uievent.DialogFragment" android:label="DialogFragment" /> V/FooFragment: Click ShowDialog V/FooFragment: Before Call Navigate V/FooFragment: After Call Navigate V/DialogFragment: onAttach V/DialogFragment: onCreate V/DialogFragment: onCreateDialog V/DialogFragment: onActivityCreated V/DialogFragment: onStart V/DialogFragment: onResume button_navigate_bar.setOnClickListener { this@FooFragment.logv("Click NavigateBarMaybeCrash") this@FooFragment.logv("Before Call Navigate") findNavController().navigate(R.id.action_fooFragment_to_barFragment) this@FooFragment.logv("After Call Navigate") } Fragment will will not enter onStop when showing a dialogFragment
18. button_navigate_bar.setOnClickListener { findNavController().safeNavigate( R.id.fooFragment, R.id.action_fooFragment_to_barFragment ) } Show dialog:
19. Throttle the navigation destination
20. button_navigate_bar.setOnClickListener { findNavController().navigate(R.id.action_fooFragment_to_barFragment) } Show dialog:
21. V/FooFragment: Click NavigateBaz V/FooFragment: Before Call Navigate V/FooFragment: After Call Navigate V/FooFragment: onPause V/BazActivity: onCreate V/BazActivity: onStart V/BazActivity: onResume V/FooFragment: onStop V/FooFragment: Click NavigateBaz V/FooFragment: Before Call Navigate V/FooFragment: After Call Navigate V/FooFragment: onPause V/BazActivity: onCreate V/BazActivity: onStart V/BazActivity: onResume V/FooFragment: Click NavigateBaz V/FooFragment: Before Call Navigate V/FooFragment: After Call Navigate V/BazActivity: onPause V/BazActivity: onCreate V/BazActivity: onStart V/BazActivity: onResume V/BazActivity: onStop V/FooFragment: onStop Navigate to Activity once: Navigate to Activity twice: - No Crash - CurrentDestinationId not changed
22. BaseFragment.kt: abstract class BaseFragment : Fragment() { @IdRes open val navId: Int = 0 protected fun navigate(@IdRes destId: Int) { require(navId != 0) { "Need fragment id in navGraph for safe navigation" } findNavController().safeNavigate(desId) } }
23. BaseFragment.kt: abstract class BaseFragment : Fragment() { @IdRes open val navId: Int = 0 protected fun navigate(@IdRes destId: Int) { require(navId != 0) { "Need fragment id in navGraph for safe navigation" } if (viewLifecycleOwner.lifecycle.currentState.isAtLeast(Lifecycle.State.RESUMED)) { findNavController().safeNavigate(desId) } } }
24. button_navigate_baz.setOnClickListener { navigate(R.id.action_fooFragment_to_bazActivity) navigate(R.id.action_fooFragment_to_bazActivity) } Two Activities will still be launched …
25. button_navigate_baz.setOnClickListener { navigate(R.id.action_fooFragment_to_bazActivity) } Good enough to deal with the general situation
26. • Check current destination ID before navigation to avoid the crash • Do navigation after onResume to avoid launch duplicate Activities Recap
27. Thank you!