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 .
Related
My project
Single activity pattern with fragments in kotlin.
Navigation component + bottom navigation view together.
There are four tabs(fragments) in bottom navigation view.
My issue is changing each tab in bottom navigation, then each fragment is re-created which due to the app is laggy.
So my target is making only one instance of each fragment there.
What I tried is:
adding app:launchSingleTop="true" for the tab fragment in grap.xml. DOESN'T WORK.
This idea is if the tab fragment can be pop backed then use it directly or create new. But this only works sometimes. Some times the tab fragment does not re-created but some times are!
I think the reason is pop back stack clear it for some time? Not sure.
binding.bottomNavigationView.setOnItemSelectedListener { item: MenuItem ->
if (!navController.popBackStack(item.itemId, false)) {
NavigationUI.onNavDestinationSelected(item , navController)
}
true
}
I used navController.navigate(item.itemId, null, NavOptions.Builder().setPopUpTo(item.itemId, false).build()) to replace NavigationUI.onNavDestinationSelected(item , navController), still doesn't work.
Any idea? thanks!
just add this piece of code to avoid recreation
binding.bottomNavigationView.setOnItemReselectedListener { }
I have a bottom navigation bar which is connected with navHost and is configured using the following code:
Val navHostFragment =supportFragmentManager.findFragmentById(R.id.fragment) as NavHostFragment
val navController = navHostFragment.navController
val bottomNavBar = findViewById<BottomNavigationView>(R.id.bottomBar)
setupWithNavController(bottomNavBar, navController)
I have 4 fragments now when I switch to 2nd fragment(by clicking on 2nd icon in the bottom navigation bar) and then I navigate to another fragment which is linked to the 2nd fragment. When I click on the back button I switch to 2nd fragment.
All good till far.
The problem is: I want to go back to 2nd fragment from the opened fragment when I reselect the same icon in the bottom navigation bar
I solved my issue with the help of this thread. If someone is facing the same issue, check this out:
Android clear backstack after reselecting Bottom Navigation tab
I have integrated a better solution which lets you have animations too when switching from one fragment to another.
val id = navController.currentDestination?.id
when (id) {
R.id.detailedTransactionAnalysis -> {
navController.navigate(R.id.action_detailedTransactionAnalysis_to_MainScreen)
}
R.id.detailedCategoryTransactionsFragment -> {
navController.navigate(R.id.action_detailedCategoryTransactionsFragment_to_MainScreen)
}
R.id.addTransaction -> {
navController.navigate(R.id.action_addTransaction_to_Stats)
}
}
navController.popBackStack(reselectedDestinationId, inclusive = false)
It works totally fine.
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
}
I implemented conditional navigation to my LoginFragment, with android navigation architecture component. The problem I facing now, is that I would like to hide the up button on the toolbar, and the disable any in-app navigation while the user is not logged in.
I would like to be able to implement this with a one-activity approach, where the Activity sets up the in app navigation UI and the navController like in the android sunflower demo, and the navigation destinations are Fragments.
I implemented the conditional navigation as discribed here:
Navigation Architecture Component - Login screen
How can I properly implement hiding the navigation and the up button on the login screen, with Navigation Architecture Component?
I don't know exactly what you mean by hiding navigation, but I will assume you mean hiding a drawer layout. To hide the up button and lock the drawer add the following to your MainActivity's onCreate. I'm using Kotlin.
myNavController.addOnDestinationChangedListener { _, destination ->
if (destination.id == R.id.loginFragment) {
myDrawerLayout.setDrawerLockMode(DrawerLayout.LOCK_MODE_LOCKED_CLOSED)
myToolbar.setVisibility(View.GONE)
} else {
myDrawerLayout.setDrawerLockMode(DrawerLayout.LOCK_MODE_UNLOCKED)
myToolbar.setVisibility(View.VISIBLE)
}
To make just the up button go away use myToolbar.setNavigationIcon(null) and to make it come back use myToolbar.setNavigationIcon(R.id.my_icon)
My method is adding the login page to the root set
val navController = findNavController(R.id.main_nav_host)
val appBarConfiguration = AppBarConfiguration(setOf(R.id.home_dest,
R.id.user_dest,R.id.login_dest))
toolbar.setupWithNavController(navController, appBarConfiguration)
So when you are on the login page, there is no back button.
System back button can override onBackPressed()
override fun onBackPressed() {
if (findNavController(R.id.main_nav_host).currentDestination?.id != R.id.next_dest)
super.onBackPressed()
}
}
Sorry for my English
I am using Navigation Component with Navigation Drawer.
I have added Fragments for each Navigation item in the menu.
Add NavHostFragment where this Fragment will be swapped
Then added Fragments as Destinations
I want master Detail Navigation i.e.
start destination -> fragment 2
back button -> start destination
start destination -> fragment 2 -> fragment 3 -> fragment 4
back button -> start destination
My question is whether I should add any connections to this graph?
I also need to have one menu item which is just logout function call not fragment swapping, so I could not configure it with default setup
val navController = findNavController(R.id.main_nav_host_fragment)
nav_view.setupWithNavController(navController)
But rather have to use
nav_view.setNavigationItemSelectedListener(this)
override fun onNavigationItemSelected(item: MenuItem): Boolean {
// Handle navigation view item clicks here.
when (item.itemId) {
R.id.navSignOut -> {
loginViewModel.logout()
}
else -> {
val navController = findNavController(R.id.main_nav_host_fragment)
navController.navigate(item.itemId)
}
}
drawer_layout.closeDrawer(GravityCompat.END)
return true
}
I also need to show Login Activity above (modally) the Main App Activity with Navigation Drawer. Can I use Navigation Graph for it and how?
Login Activity should: on back button -> close app, if logged out -> start above main activity, if logged in go to main activity
So I have to questions:
1. Should I use any actions?
2. Should I use custom navigation for drawer or setupWithNavController()?
3. What about modal login activity navigation?
The part I undrestood from your question is how to navigate to logout.
Usually when the user clicks on logout you want to log them out and navigate to a startup screen.
So you need to add your startup activity to nav_graph.
Michael, navigation architecture it is not that easy to understand at the beginning, what you want to is not the exception. But as this navigation is new, I just suggest you to follow the code lab.
https://codelabs.developers.google.com/codelabs/android-navigation/#0
I see for instance your line to close the drawer. The code lab has instructions on how to setup the nav drawer with navigation and the UI
I hope it helps you.