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Navigation drawer for fragment navigation doesn't know how to go back to main fragment after screen turn off or app going in the background

I have a single activity app that uses navigation graph and a navigation drawer to go to some of the fragments. Pressing back from each of the fragments usually brings me back to the main fragment, UNLESS I turn the screen off and back on or I put the app in the background. When I resume the app, the up button widget turns back into a hamburger menu, but navigation doesn't happen. Pressing the android back button doesn't navigate either, as if the app forgets where to navigate to.
val navController = (supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as NavHostFragment).navController
setSupportActionBar(layoutAppBarMain.layoutToolbarMain)
NavigationUI.setupActionBarWithNavController(this#MainActivity, navController, mainDrawerLayout)
appBarConfiguration = AppBarConfiguration(navController.graph, mainDrawerLayout)
NavigationUI.setupWithNavController(mainActivityNavView, navController)
supportActionBar?.setDisplayShowTitleEnabled(false)
navController.addOnDestinationChangedListener { _: NavController, nd: NavDestination, _: Bundle? ->
when (nd.id) {
R.id.playFragment -> mainDrawerLayout.setDrawerLockMode(DrawerLayout.LOCK_MODE_UNLOCKED)
R.id.navRulesFragment, R.id.navImproveFragment, R.id.navAboutFragment, R.id.navDonateFragment -> mainDrawerLayout.setDrawerLockMode(
DrawerLayout.LOCK_MODE_LOCKED_CLOSED)
else -> {
binding.layoutAppBarMain.layoutToolbarMain.navigationIcon = null
mainDrawerLayout.setDrawerLockMode(DrawerLayout.LOCK_MODE_LOCKED_CLOSED)
}
}
}
Then overriding the onSupportNavigateUp():
override fun onSupportNavigateUp(): Boolean {
return NavigationUI.navigateUp(navController, appBarConfiguration) || super.onSupportNavigateUp()
}

If you don't have below code just add and try again:
override fun onSupportNavigateUp(): Boolean {
return NavigationUI.navigateUp(navController, null) || super.onSupportNavigateUp()
}
Edit: If that doesn't work then try this:
layoutAppBarMain.layoutToolbarMain.setNavigationOnClickListener { onBackPressed() }

I found out what was causing it. I was using postponeEnterTransition() to check if the database was empty. If it is, then it should load the first fragment, else the second fragment. The problem was that I was using startPostponedEnterTransition() after the navigation had already left the first fragment, which was causing the navController to misbehave.
To solve this, I am now starting the enter transition in the first fragment, then hiding it, before navigating to the second fragment. I am also using a splash screen which is being turned off after the navigation is complete.
In MainActivity:
val splashScreen = installSplashScreen()
splashScreen.setKeepOnScreenCondition { mainVm.keepSplashScreen.value }
super.onCreate(savedInstanceState)
In onCreateView of the first fragment:
postponeEnterTransition() // Wait for data to load before displaying fragment
mainVm.matchState.observe(viewLifecycleOwner, EventObserver { matchState ->
when (matchState) {
RULES_IDLE -> mainVm.transitionToFragment(this, 0)
// Here, if database is not empty,
// start transition right away and hide the view only then navigate
// If the transition happens after the navigation has started,
// the navController will have issues returning from the navDrawer fragments.
GAME_IN_PROGRESS -> {
startPostponedEnterTransition()
view?.visibility = GONE
navigate(RulesFragmentDirections.gameFrag()
}
else -> Timber.e("No implementation for state $matchState at this point")
}
})
Within the MainViewModel:
private val _keepSplashScreen = MutableStateFlow(true)
val keepSplashScreen = _keepSplashScreen.asStateFlow()
fun transitionToFragment(fragment: Fragment, ms: Long) = viewModelScope.launch {
fragment.startPostponedEnterTransition()
delay(ms) // Add a delay for the content to fully load before turning off the splash screen
_keepSplashScreen.value = false
}
Aside from this, the navController implementation works correctly as per the post above.

handleOnBackPressed not working on one fragment

I'm using navigation componetns with drawer and app bar in my program.
From home fragment, it has a recyclerview, and when each item is clicked, the nav_host_fragment host another fragment with the selected itme, using the following line:
Navigation.findNavController(view).navigate(R.id.doTimedTaskFragment, args);
The problem, is, I need to ask user if they want to give up the progress they made in the new fragment (doTimedTaskFragment) if they hit the back button in app bar.
I digged Google Document and in the following link gives how I should do it.
https://developer.android.com/guide/navigation/navigation-custom-back#java
public class MyFragment extends Fragment {
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// This callback will only be called when MyFragment is at least Started.
OnBackPressedCallback callback = new OnBackPressedCallback(true /* enabled by default */) {
#Override
public void handleOnBackPressed() {
// Handle the back button event
}
};
requireActivity().getOnBackPressedDispatcher().addCallback(this, callback);
// The callback can be enabled or disabled here or in handleOnBackPressed()
}
...
}
However, handleOnBackPressed() never gets called, and I'm suspecting the line of code I've used above to direct to the new fragment, and I can't find a way to resolve this issue.
EDIT/UPDATE:
My question was originally asking how to handle clicking Navigation component left(back) arrow click behavior, and in my case, I overrodeonOptionsItemSelected inside the fragment and code came to be way much cleaner and better than overriding inside MainActivity.
Here's screenshot of my mobile navigation.xml

The OnBackPressedCallback is called for back button on the device not the Toolbar back button. For the toolbar back button you have to set it up with the navigation controller.
In your activity's onCreate:
setSupportActionBar(findViewById(R.id.toolbar))
val nc = findNavController(this, R.id.nav_host_fragment)
val appBarConfiguration = AppBarConfiguration.Builder(nc.graph).build()
setupActionBarWithNavController(
this,
nc,
appBarConfiguration
)
and then:
override fun onSupportNavigateUp(): Boolean {
//Handle the toolbar back button here.
val navController = findNavController(this, R.id.nav_host_fragment)
navController.currentDestination?.let {
if (it.id == R.id.someFragment) {
//do something here
} else {
navController.popBackStack()
}
}
return super.onSupportNavigateUp()
}

Alternate for onSupportNavigateUp of activity in fragment with single activity and navigation componnet

I am using onSupportNavigateUp() in activity and now i am moving to use single activity architecture and navigation component problem is that i stuck here i don't find any elternative to onSupportNavigateUp() and onBackPressed() in fragment and navcontroller
override fun onSupportNavigateUp(): Boolean {
// some code like showing ad
onBackPressed()
return super.onSupportNavigateUp()
}
but i find solution solution onBackPressed() with onBackPressedDispatcher but problem is that is only work when navigation bar back button pressed not for toolbar up button
requireActivity().onBackPressedDispatcher.addCallback(this) {
// some code like showing ad
}

for me, that work is you have set up navigation component with toolbar like this
toolbar.setupWithNavController(findNavController())
toolbar.setNavigationOnClickListener {
// some code
findNavController().navigateUp()
}

shared element transition is not working when using toolbar home

I'm currently running into a strange problem, similar to here Shared element transition when using ActionBar Back button but with a fragment to fragment shared element transition. It works fine when using the back button. As soon as the toolbar home is triggered it's just blinking. So calling finishAfterTransition() is no option here.
I call the same method both times. The base for back navigation
override fun onBackPressed() {
if (coordinator != null) {
coordinator!!.back()
} else {
finish()
}
}
and the intercepted toolbar home click.
override fun onOptionsItemSelected(item: MenuItem?): Boolean {
return when (item?.itemId) {
android.R.id.home -> {
onBackPressed()
true
}
else -> return super.onOptionsItemSelected(item)
}
}
Update: Now I noted like one out of ten tries it works correctly.
I hope anyone of you guys has a clue why this happens.
Regards coffeelord

Cannot custom Actionbar's navigate up method

In the activity class, I set up the actionbar as this:
MyActivity
setSupportActionBar(findViewById(R.id.toolbar_my))
supportActionBar?.apply {
setDisplayHomeAsUpEnabled(true)
setDisplayShowHomeEnabled(true)
}
Because I need to override onOptionsItemSelected(...) (in the fragment class), I didn't override onSupportNavigateUp() here.
This activity cotnains a fragment. What I want is, when click on the actionbar up button, besides pop back, also revoke a custom save() method.
So in the fragment's onOptionsItemSelected(...), write some code for the item.id == android.R.id.home case. However, I made a break point here, and found that when click on the up/home button, the code in the android.R.id.home case is never revoked. The other items' on selected methods work.
In the fragment class:
MyFragment
override fun onOptionsItemSelected(item: MenuItem?): Boolean {
when (item?.itemId) {
android.R.id.home -> {
// code here not gets called when click up/home button
mPresenter.save()
return true
}
R.id.edit-> {
// The code here is revoked when item selected.
}
else -> {
return super.onOptionsItemSelected(item)
}
}
}
I tried override another onOptionsItemSelected(...) method in the activity class, and write android.R.id.home case, still cannot invoke methods in it.
Why the code in item.id == android.R.id.home case is not called?

Read setHomeButtonEnabled
Enable or disable the "home" button in the corner of the action bar.
(Note that this is the application home/up affordance on the action
bar, not the systemwide home button.)
supportActionBar?.setHomeButtonEnabled(true)
supportActionBar?.setDisplayHomeAsUpEnabled(true)
Then
override fun onOptionsItemSelected(item: MenuItem): Boolean {
when (item.getItemId()){
android.R.id.home -> {
mPresenter.save()
return true
}
R.id.edit-> {
// some code
}
}
return super.onOptionsItemSelected(item)
}