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Android navigation component display multiple DialogFragments in a row

Hi folks I need to throw up a series of DialogFragments one after another using the navigation component. I have encountered some pretty unusual system behavior which looks like a race condition. I show the dialogs with a global action after an item is clicked, and use the fragment result api to determine if another one should be shown.
I am using a custom layout so there's no positive / negative listeners etc., and my own continue / cancel buttons send a result back to the host fragment.
ItemsFragment.kt:
navController.navigate(RegisterItemsDirections.openModsDialog(item.id, 0))
fragment.setFragmentResultListener(ItemsFragment.MODIFIERS_REQUEST) { key, bundle ->
//kill the current dialog
navController.navigateUp()
//some logic to determine if we need another dialog...
if(needAnotherDialog){
//navigate to the next one
navController.navigate(RegisterItemsDirections.openModsDialog(item.id, lastModGroupSelectionIndex + 1))
}
}
ModsDialogFragment.kt, when the user clicks "continue"
setFragmentResult(MODIFIERS_REQUEST, bundleOf(MODIFIERS_RESULT to selectedMods))
So the issue only appears on 3rd or more dialogs on my devices, I can see that the 1st and 2nd dialogs are completely destroyed and detached. When it displays the 3rd one, the first one attaches itself again, and appears beneath the 3rd one which I can't explain.
I've tried:
Popping the back stack in the global action's nav xml
Navigating up or dismissing the dialog fragment in the dialog itself (before calling setFragmentResult), which is the most logical place to put it
Popping the backstack instead of navigating up, basically the same thing in this case
When I don't dismiss / nav up any of the dialogs and allow them all to just stack, there's no issue. When I delay the navigation by 500ms there is no issue. So navving up and then immediately navigating to another instance of the dialog are fighting with eachother producing very strange results. What could be the solution here that doesn't involve a random delay?
Navigation version is 2.3.3 and I'm having a lot of trouble trying to update it due to AGP upgrades being incompatible with a jar I need so I'm not sure if this has been fixed.

I figured out the issue, it's down to dumb copy pasting.
I took the donut tracker sample code and made it stack dialogs in the same way and there was no issue.
The difference between the two was I am subclassing DialogFragment and for some unknown reason doing this:
override fun show(manager: FragmentManager, tag: String?) {
val transaction = manager.beginTransaction()
val prevFragment = manager.findFragmentByTag(tag)
if (prevFragment != null) {
transaction.remove(prevFragment)
}
transaction.addToBackStack(null)
show(transaction, tag)
}
This code predates the Nav component library I believe, and it completely f***s with the fragment manager used by the navigation component. So the moral of the story is to not do bizarre things in super classes, or better yet not super class at all.

Navigation Controller (Managing Backstack) Jetpack Android

Good day. So I've been working around with NavComponent of Jetpack for Android
I've thought that management of BackStack of fragments had to be implemented there already, well in fact it is there but I have faced an issue.
Here is my structure:
I have and entry Activity
I have a NavHost in the activity
I have Bottom Navigation bar in the Activity
For each Bottom Item I am using separate Fragments to navigate through.
Here is the code for the navigation.
bottomNavigationView.setOnNavigationItemSelectedListener {
when (it.itemId) {
R.id.navigation_home -> {
navController.apply {
navigate(R.id.navigation_home)
}
true
}
R.id.navigation_dashboard -> {
navController.apply {
navigate(R.id.dashboardFragment)
}
true
}
R.id.navigation_notifications -> {
true
}
else -> {
false
}
}
}
Never mind the last item.
So the issue is next.
If I try to switch between home and dashboard multiple times, when I press back then the stack surely will start popping all the items included there. So if I move like 6 times it will take me 12 attempts to actually exit the app.
Currently I couldn't find any source where for example the navigate() method will accept some sort of argument to cash my fragments instead of recreating it each time and adding to the BackStack.
So what kind of approach would you suggest?
If I to manage the BackStack manually on each back button pressed, what's the purpose of NavController at all? Just for creating and FORWARD navigation?
I think I'm missing some source in Android's official docs.
Thank you beforehand.
P.S.
using navController.popBackStack() before calling navigate() surely isn't the correct choice.

According to the documentation here :
NavigationUI can also handle bottom navigation. When a user selects a menu item, the NavController calls onNavDestinationSelected() and automatically updates the selected item in the bottom navigation bar.
to do so you have to give your bottom navigation items an ids as same as the corresponding destination in your navigation graph , and then tie you bottom view to the controller like this :
NavHostFragment navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host_fragment);
NavController navController = navHostFragment.getNavController();
BottomNavigationView bottomNav = findViewById(R.id.bottom_nav);
NavigationUI.setupWithNavController(bottomNav, navController);
Note : from my personal experience , when the startDestination in the graph , that start by default is not currently in back stack (In my case it was the landing page which i pop it out when going to home fragment) then the app act with weird behavior like this . so make sure the start destination is existed in your back stack on should work fine .

FragmentScenario and nested NavHostFragments don't perform navigations as expected in Instrumentation tests

I am writing a single Activity app that uses Android's Navigation Components to help with navigation and Fragment Scenario for instrumentation testing. I have run into a performance discrepancy when using the back button between the actual app navigation behavior and the behavior of a Fragment being tested in isolation during an Instrumentation tests when using fragment scenario.
In my MainActivity I have a main NavHostFragment that takes up the entire screen. I use that nav host fragment to show several screens including some master detail fragments. Each master detail fragment has another NavHostFragment in it to show the different detail fragments for that feature. This setup works great and provides the behavior I desire.
To accomplish the master detail screen I use a ParentFragment that has two FrameLayouts to create the split screen for tablet and for handset I programatically hide one of the FrameLayouts. When the ParentFragment is created, it detects if it is being run on a tablet or handset and then programatically adds a NavHostFragment to the right frame layout on tablet, and on handset hides the right pane adds a NavHostFragment to the left pane. The NavHostFragments also have a different navigation graph set on them depending on if they are being run on tablet or handset (on handset we show fragments as dialogs, on tablet we show them as regular fragments).
private fun setupTabletView() {
viewDataBinding.framelayoutLeftPane.visibility = View.VISIBLE
if (navHostFragment == null) {
navHostFragment = NavHostFragment.create(R.navigation.transport_destinations_tablet)
navHostFragment?.let {
childFragmentManager.beginTransaction()
.add(R.id.framelayout_left_pane, it, TRANSPORT_NAV_HOST_TAG)
.setPrimaryNavigationFragment(it)
.commit()
}
}
if (childFragmentManager.findFragmentByTag(SummaryFragment.TAG) == null) {
childFragmentManager.beginTransaction()
.add(R.id.framelayout_right_pane, fragFactory.instantiate(ClassLoader.getSystemClassLoader(), SummaryFragment::class.java.canonicalName!!), SummaryFragment.TAG)
.commit()
}
}
private fun setupPhoneView() {
viewDataBinding.framelayoutLeftPane.visibility = View.GONE
if (navHostFragment == null) {
navHostFragment = NavHostFragment.create(R.navigation.transport_destinations_phone)
navHostFragment?.let {
childFragmentManager.beginTransaction()
.replace(R.id.framelayout_left_pane, it, TRANSPORT_NAV_HOST_TAG)
.setPrimaryNavigationFragment(it)
.commit()
}
}
}
When running the devDebug version of the app, everything works as expected. I am able to navigate using the main NavHostFragment to different master-detail screens. After I navigate to the master-detail screen, the nested NavHostFragment takes over and I can navigate screens in and out of the master detail fragment using the nested NavHostFragment.
When the user attempts to click the back button, which would cause the to leave the master detail screen and navigate to the previous screen, we pop up a dialog to the user asking if they really want to leave the screen (it's a screen where they enter a lot of data). To accomplish this we register an onBackPressDispatcher callback so we know when the back button was pressed and navigate to the dialog when the callback is invoked. In the devDebug version, the user begins by being at location A on the nav graph. If, when they are at location A, they click the back button, then we show a dialog fragment asking if the user really intends to leave the screen. If, instead, the user navigates from location A to location B and clicks back they are first navigated back to location A. If they click the back button again, the back press dispatcher callback is invoked and they are then shown the dialog fragment asking if they really intent to leave location A. So it seems that that the back button affects the back stack of the nested NavHostFragment until the nested NavHostFragment only has one fragment left. When only one fragment is left and the back button is clicked, the onBackPressDisapatcher callback is invoked. This is exactly the desired behavior. However, when I write an Instrumentation test with Fragment Scenario where I attempt to test the ParentFragment I have found that the back press behavior is different. In the test I use Fragment Scenario to launch ParentFragment, I then run a test where I do a navigation in the nested NavHostFragment. When I click the back button I expect that the nested nav host fragment will pop its stack. However, the onBackPressDispatcher callback is invoked immediately instead of after the nested nav host fragment has one fragment left on its stack.
I set some breakpoints in the NavHostFragment and it seems that when the tests are run, the NavHostFragment is not setup to intercept back clicks. Its enableOnBackPressed() method is always called with a flag set to false.
I don't understand what about the test setup is causing this behavior. I would think that the nav host fragment would intercept the back clicks itself until it only had one fragment left on its backstack and only then would the onBackPressDispatcher callback be invoked.
Am I misunderstanding how I should be testing this? Why does the onBackPressDispatcher's callback get called when the back button is pressed.

As seen in the FragmentScenario source code, it does not currently (as of Fragment 1.2.1) use setPrimaryNavigationFragment(). This means that the Fragment being tested does not intercept the back button and hence, its child fragments (such as your NavHostFragment) do not intercept the back button.
You can set this flag yourself in your test:
#Test
fun testParentFragment() {
// Use the reified Kotlin extension to launchFragmentInContainer
with(launchFragmentInContainer<ParentFragment>()) {
onFragment { fragment ->
// Use the fragment-ktx commitNow Kotlin extension
fragment.parentFragmentManager.commitNow {
setPrimaryNavigationFragment(fragment)
}
}
// Now you can proceed with your test
}

How to show "up" / "back" button in Xamarin.Forms?

I am trying to work out how to show the "up" arrow in Xamarin.Forms without a pushing a page onto the stack. I.E. I just want to perform an action when the back button is pressed. I am completely stuck on this so any help would be appreciated.
I have tried creating a custom renderer which handles a view property called DisplayHomeAsBack. Which in the renderer calls the following:
FormsAppCompatActivity context = ((FormsAppCompatActivity)Forms.Context);
Android.Support.V7.App.ActionBar actionBar = context.SupportActionBar;
if (actionBar != null)
{
actionBar.SetDisplayHomeAsUpEnabled(element.DisplayHomeAsBack);
}
Unfortunately it seems this does absolutely nothing, even though all online tutorials and stackoverflow question for android suggest this method.
The plan is that I can then use the "OnBackButtonPressed" override in MasterDetailPage, which should allow me to perform this action. Unfortunately displaying the back button has been the larger hurdle so far!
Any idea of a better way to do this or how I can get the current mechanism to work?
EDIT
I have created a project and uploaded it to this question on the Xamarin support forums, if it helps.
http://forums.xamarin.com/discussion/comment/186330#Comment_186330

Sorry to keep you waiting so long!
Warning that I did not actually run this code and changed it from my own so I would be surprised if it worked perfectly without some changes.
So below should add a back button where there was not one before (so like when there is not really a page to go back to) and then we will add a custom action to perform when it gets pressed.
I would suggest you push a new page onto the stack without using animation so it is transparent to the user and also makes all of this much simpler, but if you absolutely do not want to do that, the below method should work.
MainActivity:
//Use this to subscribe to the event which will create the back button
public override bool OnCreateOptionsMenu(IMenu menu) {
if(menu != null && App.AppMasterPage != null) { //You will need this to make sure you are on your MasterDetailPage, just store a global reference to it in the App class or where ever
Xamarin.Forms.MessagingCenter.Unsubscribe<string>(this, "CreateBackButton");
Xamarin.Forms.MessagingCenter.Subscribe<string>(this, "CreateBackButton", stringWeWillNotUse => { //Use this to subscribe to the event that creates the back button, then when you want the back button to show you just run Xamarin.Forms.MessagingCenter.Send<string>(this, "CreateBackButton")
ActionBar.DisplayOptions = ActionBarDisplayOptions.ShowTitle | ActionBarDisplayOptions.ShowHome | ActionBarDisplayOptions.UseLogo | ActionBarDisplayOptions.HomeAsUp; //You may need to play with these options to get it working but the important one is 'HomeAsUp' which should add the back button
});
} else {
Xamarin.Forms.MessagingCenter.Unsubscribe<string>(this, "CreateBackButton");
}
return base.OnCreateOptionsMenu(menu);
}
Now the next step is do do a custom action when it is pressed. I think you can either override OnBackPressed() or OnOptionsItemSelected() in MainActivity or maybe you can override the MasterDetailPage method. I am not sure.
Which ever one works for you, inside of that override, I would simply check to see if you are on your App.AppMasterPage like we did above, and if so, send a MessagingCenter message which your App.AppMasterPage has already subscribed to in order for it to handle the custom action.
If you get stuck let me know!

I know it sounds like a bit of a hack, but the best "solution" I have found so far is to add a page behind the current page (behind the root) so it is not visible. Then when the user presses the back button, handle it by removing that page.

Handle back action for multiple view

I have an activity which have multiple piece of UI panel(you can think them as view in android), these panels will be invisible by default.
Now when user trigger action1, PanelA will display, when trigger action2, PanelB will display(at different location of the screen).
Both PanelA and PanelB is visible at the moment, now when user hit the back menu, the PanelB should disappear, and PanelA should disappear when hit the back menu again.
At first, I use View to hold different panels, however I found it is difficult to keep the state consist, for example, the activity will be a little different between PanelA and PanelB.
Then I found the fragment, however after I tried and tested, I found that the addTobackStack() can not apply to my us-case, since the PanelA and PanelB are at different location, android can not save their state by default.
So I wonder if there is any other solution for my requirement?

You need to manually handle this scenario inside onBackPressed() method of an Activity.
For instance -
#Override
public void onBackPressed() {
if (panelB.isOpened()) {
panelB.close()
} else if (panelA.isOpened()) {
panelA.close()
} else {
super.onBackPressed();
}
}
When panelB is opened, it will close only panelB and wont do anything else. Same goes for panelA, if its opened and when both the panel are closed then it will exit the app like normal.
I highly recommend to use DialogFragments here as you can call show() and dismiss() any point of time on that and they can handle custom views pretty well.
Hope it helps.