I need to display custom AlertDialog
, but only when there are no more fragments after calling NavController.navigateUp()
. My current code does something similar, but there is a bug to it:
override fun onBackPressed() {
if (navController.navigateUp()) {
return
}
showQuitDialog()
}
This somewhat works, but if I cancel the AlertDialog
and don't quit the app, navController
already navigated up to NavGraph
root, which is not the fragment in which I was when AlertDialog
appeared. So, if I try to use any navigation action from that fragment, I get error:
java.lang.IllegalArgumentException: navigation destination com.example.test/actionNavigateToNextFragment is unknown to this NavController
This could be resolved, if I had access to mBackStack
field in NavController
, but it's package private
, and I can't use reflection in my current project. But if it was public
, I would use it the following way:
override fun onBackPressed() {
// 2 because first one is NavGraph, second one is last fragment on the stack
if(navController.mBackStack.size > 2) {
navController.navigateUp()
return
}
showQuitDialog()
}
Is there a way to do this without reflection?
You can compare the ID of the start destination with the ID of the current destination. Something like:
override fun onBackPressed() = when {
navController.graph.startDestination == navController.currentDestination?.id -> showQuitDialog()
else -> super.onBackPressed()
}
Hope it helps.