Ignoring navigate() call - android

I am using the new android Navigation Framework in one of my Applications.
The purpose of Application is to behave as a launcher.
Sometimes when I try to change the fragment (navigate using the navcontroller) it doesn't change the fragment instead it logs
Ignoring navigate() call: FragmentManager has already saved its state
i know this question been asked before here Ignoring navigate() call: FragmentManager has already saved its state
but it doesn't have a Solution.
I am navigating using the following code:
Navigation.findNavController(view).navigate(R.id.action_next, bundle)

I had the same problem, in my case I was trying to use navigate() inside the Mopub ad callback onInterstitialDismissed, and was getting this info.
My solution for this case to use LiveData like this:
private var dismissState = MutableLiveData<Int>(0)
mMobupInterStitialAd?.interstitialAdListener = object : MoPubInterstitial.InterstitialAdListener {
override fun onInterstitialDismissed() {
dismissState.value=1
}
}
override fun onViewCreated() {
dismissState.observe(viewLifecycleOwner) {
if(it == 1) {
findNavController.navigate(R.id.fragmentAtoFragmentB)
}
}
}
This is how I solved the problem.

Related

StateFlow fetching the same data again on Back Navigation

I am working with RecyclerView and using Retrofit to fetch the data from Server. I am using Kotlin with MVVM Design Pattern. I have used LiveData it was working fine. But with Stateflow causing issues when we navigate to another Fragment and Comes back to the Same Fragment again. It just fetches the same data again. Below is the code for ViewModel and the observer:
//View Model
private val _allTimeSheetsResponse =
MutableStateFlow<ResponsesResult<AllTimeSheetsResponse>>(ResponsesResult.Empty)
val allTimeSheetsResponse : StateFlow<ResponsesResult<AllTimeSheetsResponse>> get() = _allTimeSheetsResponse
fun getAllTimeSheets(auth: String) =
viewModelScope.launch {
timeSheetsRepository.getAllTimeSheets(auth).collect {
_allTimeSheetsResponse.value = it
}
}
//Observer
lifecycleScope.launchWhenStarted{
timeSheetsViewModel.allTimeSheetsResponse.collect { timeSheetsResponse ->
when (timeSheetsResponse) {
is ResponsesResult.Loading -> binding.progressBarLayout.show()
is ResponsesResult.Failure -> {
binding.progressBarLayout.gone()
binding.nothingFoundLayout.show()
handleApiError(timeSheetsResponse)
}
is ResponsesResult.Success -> {
binding.progressBarLayout.gone()
if (timeSheetsResponse.value.payload.isNotEmpty()) {
showAllTimeSheetsRecyclerAdapter.submitList(timeSheetsResponse.value.payload)
} else {
binding.nothingFoundLayout.show()
}
}
else -> Unit
}
}
}
Because you call getAllTimeSheets many times (eg. onCreateView or onViewCreated). Trying call it when accessing allTimeSheetsResponse` for the first time.
Your ViewModel's getAllTimeSheets() function starts a new coroutine to collect from the repo's cold Flow each time you call it, so each time the Fragment comes back, presumably. You should remove this function and simply convert the repo's cold Flow directly to a StateFlow:
val allTimeSheetsResponse: StateFlow<ResponsesResult<AllTimeSheetsResponse>> =
timeSheetsRepository.getAllTimeSheets(auth)
.stateIn(viewModelScope, SharingStarted.Eagerly, ResponsesResult.Empty)
You can pass the auth parameter into the ViewModel's factory through to its constructor.
When you are using the navigationComponent and call navController.navigate() to open a fragment, in the background destination fragment replaces with the old destination's fragment. so old fragment will keep in the fragmentManager backStack. but its view will destroy. and when navigate back, old fragment comes from backStack (not created again) and just its view creates.
So it's better to call getAllTimeSheets() in Fragment's onCreate. (to call one time). When fetching done, all data will set in _allTimeSheetsResponse
And then you should observe allTimeSheetsResponse in onViewCreated with viewLifecycleOwner scope.
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewModel.allTimeSheetsResponse.onEach { response ->
// do sth with response
}.launchIn(viewLifecycleOwner.lifecycleScope)
}
fun getAllTimeSheets(auth: String) :StateFlow<ResponsesResult<AllTimeSheetsResponse>> {
var mutableStateFlow = MutableStateFlow<ResponsesResult<AllTimeSheetsResponse>>(ResponsesResult.Empty)
viewModelScope.launch {
timeSheetsRepository.getAllTimeSheets(auth).collect {
mutableStateFlow.value = it
}
}
return mutableStateFlow
}

how to stop observer to automatically observe data when pop back to previous fragment? [duplicate]

I have some problem in nested fragment in Kotlin. I have nested fragment with ViewModel. After resuming fragment from back button press all observers on viewModel LiveData triggers again although my data does not changed.
First i googled and tried for define observer in filed variable and check if it is initialized then do not observer it again:
lateinit var observer: Observer
fun method(){
if (::observer.isInitialized) return
observer = Observer{ ... }
viewModel.x_live_data.observe(viewLifecycleOwner ,observer)
}
So at first enter to fragment it works fine and also after resume it does not trigger again without data change but it does not trigger also on data change!
What is going on?
LiveData always stores the last value and sends it to each Observer that is registered. That way all Observers have the latest state.
As you're using viewLifecycleOwner, your previous Observer has been destroyed, so registering a new Observer is absolutely the correct thing to do - you need the new Observer and its existing state to populate the new views that are created after you go back to the Fragment (since the original Views are destroyed when the Fragment is put on the back stack).
If you're attempting to use LiveData for events (i.e., values that should only be processed once), LiveData isn't the best API for that as you must create an event wrapper or something similar to ensure that it is only processed once.
After knowing what happen I decide to go with customized live data to trigger just once. ConsumableLiveData. So I will put answer here may help others.
class ConsumableLiveData<T>(var consume: Boolean = false) : MutableLiveData<T>() {
private val pending = AtomicBoolean(false)
override fun observe(owner: LifecycleOwner, observer: Observer<in T>) {
super.observe(
owner,
Observer<T> {
if (consume) {
if (pending.compareAndSet(true, false)) observer.onChanged(it)
} else {
observer.onChanged(it)
}
}
)
}
override fun setValue(value: T) {
pending.set(true)
super.setValue(value)
}
}
And for usage just put as bellow. It will trigger just once after any update value. This will great to handle navigation or listen to click or any interaction from user. Because just trigger once!
//In viewModel
val goToCreditCardLiveData = ConsumableLiveData<Boolean>(true)
And in fragment:
viewModel.goToCreditCardLiveData.observe(viewLifecycleOwner) {
findNavController().navigate(...)
}
If u are using kotlin and for only one time trigger of data/event use MutableSharedFlow
example:
private val data = MutableSharedFlow<String>() // init
data.emit("hello world) // set value
lifecycleScope.launchWhenStarted {
data.collectLatest { } // value only collect once unless a new trigger come
}
MutableSharedFlow won't trigger for orientation changes or come back to the previous fragment etc

Application Crash/Navigation issue with observer when clicking "back" from fragment

I have a fragment A which sends a search query to the network, and if the result is positive uses Android navigation component to navigate to fragment B, and its done using observers.
After navigation to fragment B, i click on "<-" arrow on the top of the screen, but instead of navigating back to fragment A it reloads fragment B again. And if using the native "back" button on the device, the app crashes with "illegalArgumentException navigation destination unknown" error.
I check the internet for clues on this issue, but all i learned is that this happens because i am using .observe in onViewCreated() and when i go back, it gets called again, and because livedata has something in it already, it just navigates me back to B.
I have tried observing in onActivityCreated(), and using getViewLifeCycleOwner, but no success... the only thing that helped is checking if livedata has observers and returning if true, before using .observe, but it seems incorrect.
This is the viewModel:
private val getAssetResult = MutableLiveData<GeneralResponse<Asset>>()
private val updateAssetResult = MutableLiveData<GeneralResponse<Int>>()
private val deleteAssetResult = MutableLiveData<GeneralResponse<Int>>()
init {
state.value = ViewState(false)
Log.d(TAG, "State in init: $state")
}
fun getAssetResult(): LiveData<GeneralResponse<Asset>>{
return getAssetResult
}
fun findAsset(req: GetAssetRequest) {
scope.launch {
setProgressIndicator(true)
val result = repository.getAsset(req)
getAssetResult.postValue(result)
setProgressIndicator(false)
}
}
This is the fragment:
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewModel = ViewModelProvider(this).get(EditAssetViewModel::class.java)
setupViewModel()
initFields()
}
private fun setupViewModel() {
if (viewModel.getAssetResult().hasObservers()) // <- This is the part that prevents the app from crashing.
return
viewModel.getAssetResult().observe(this, Observer {
if (it == null) return#Observer
handleSearchResult(it)
})
if (viewModel.getState().hasObservers())
return
viewModel.getState().observe(this, Observer { handleState(it) })
}
private fun handleSearchResult(response: GeneralResponse<Asset>) {
if (response.singleValue == null) {
Toast.makeText(context!!, response.errorMessage, Toast.LENGTH_SHORT).show()
return
}
targetFragment?.let { it ->
val bundle = bundleOf("asset" to response.singleValue)
when(it) {
"UpdateLocation" ->
Navigation.findNavController(view!!).navigate(R.id.updateLocation, bundle)
"EditAsset" -> {
Navigation.findNavController(view!!).navigate(R.id.editAsset, bundle)
}
}
}
}
if i remove this part from the setupViewModel function:
if (viewModel.getAssetResult().hasObservers())
return
the app will either crash when clicked "back" using the device button or go back to fragment A, just to be navigated back to fragment B because of the .observe function.
Override the method onBackPressed() to handle the "<-" arrow
Seems like the LiveData that you use to signal to fragment A that it should navigate to fragment B is actually an event. An event happens only once and once it is consumed (navigation event is done), it is gone. Therefore, after navigating you need to send a message to the viewmodel that the navigation took place and that the corresponding data holder should be (e.g.) null again. In Fragment A you check that the new value is unequal to null, and only if this is the case, you issue the navigation event. This would prevent fragment A to immediatelly switch to B again in the back scenario.
If you want to learn more about ways to use live data for events, please refer to this article.

Android Navigation Component has lag when navigating through NavigationDrawer

I am updating my app to Navigation Architecture Components and I see that it has a lag replacing fragments which is visible in the NavigationDrawer that does not close smoothly.
Until now, I was following this approach:
https://vikrammnit.wordpress.com/2016/03/28/facing-navigation-drawer-item-onclick-lag/
So I navigate in onDrawerClosed instead than in onNavigationItemSelected to avoid the glitch.
This has been a very common issue, but it is back again. Using the Navigation Component, it is laggy again and I don't see a way to have it implemented in onDrawerClosed.
These are some older answers prior to Navigation Component
Navigation Drawer lag on Android
DrawerLayout's item click - When is the right time to replace fragment?
Thank you very much.
I'm tackling this issue as I write this answer. After some testing, I concluded that code I'm executing in fragment right after its created (like initializing RecyclerView adapter and populating it with data, or configuring UI) is causing the drawer to lag as its all happening simultaneously.
Now the best idea I got is similar to some older solutions that rely on onDrawerClosed. We delay the execution of our code in fragment until the drawer has closed. The layout of the fragment will become visible before the drawer is closed, so it will still look fast and responsive.
Note that I'm also using navigation component.
First, we are going to create an interface and implement it fragments.
interface StartFragmentListener {
fun configureFragment()
}
In activity setup DrawerListener like:
private fun configureDrawerStateListener(){
psMainNavDrawerLayout.addDrawerListener(object: DrawerLayout.DrawerListener{
override fun onDrawerStateChanged(newState: Int) {}
override fun onDrawerSlide(drawerView: View, slideOffset: Float) {}
override fun onDrawerOpened(drawerView: View) {}
override fun onDrawerClosed(drawerView: View) {
notifyDrawerClosed()
}
})
}
To notify a fragment that the drawer has been closed and it can do operations that cause lag:
private fun notifyDrawerClosed(){
val currentFragment =
supportFragmentManager.findFragmentById(R.id.psMainNavHostFragment)
?.childFragmentManager?.primaryNavigationFragment
if(currentFragment is StartFragmentListenr && currentFragment != null)
currentFragment.configureFragment()
}
In case you are not navigating to the fragment from the drawer (for example pressing back button) you also need to notify fragment to do its things. We will implement FragmentLifecycleCallbacksListener:
private fun setupFragmentLifecycleCallbacksListener(){
supportFragmentManager.findFragmentById(R.id.psMainNavHostFragment)
?.childFragmentManager?.registerFragmentLifecycleCallbacks(object : FragmentManager.FragmentLifecycleCallbacks() {
override fun onFragmentActivityCreated(fm: FragmentManager, f: Fragment, savedInstanceState: Bundle?) {
super.onFragmentActivityCreated(fm, f, savedInstanceState)
if (!psMainNavDrawerLayout.isDrawerOpen(GravityCompat.START)) {
if (f is StartFragmentListener)
f.configureFragment()
}
}
}, true)
}
In fragment:
class MyFragment: Fragment(), MyActivity.StartFragmentListener {
private var shouldConfigureUI = true
...
override fun onDetach() {
super.onDetach()
shouldConfigureUI = true
}
override fun configureFragment() {
if(shouldConfigureUI){
shouldConfigureUI = false
//do your things here, like configuring UI, getting data from VM etc...
configureUI()
}
}
}
A similar solution could be implemented with a shared view model.
Avoid the lag caused while changing Fragment / Activity onNavigationItemSelected- Android
Navigation Drawer is the most common option used in the applications, when we have more than five options then we go towards the navigation menu.
I have seen in many applications that when we change the option from the navigation menu, we observe that it lags, some people on StackOverflow recommended that use Handler like the below code:
private void openDrawerActivity(final Class className) {
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
ProjectUtils.genericIntent(NewDrawer.this, className, null, false);
}
}, 200);
}
But in the above code, it’s still not smooth & I thought why we add handler may be there is another solution after so much R&D, what I figure it out that we need to change the fragment/activity when the drawer is going to be close. let’s see with the implementation.
For more details with solution kindly go through https://android.jlelse.eu/avoid-the-lag-caused-while-changing-fragment-activity-onnavigationitemselected-android-28bcb2528ad8. It really help and useful.
Hope you find better solutions in it!

In Android Navigation Architecture, how can I check if current Fragment is the last one?

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.
Try this for any destination (you can find your destination id in the navigation graph):
private fun isDesiredDestination(): Boolean {
return with(navController) {
currentDestination == graph[R.id.yourDestinationId]
}
}
Comparing IDs of destination may not be the best solution because you may have multiple screens with the same ID but different arguments on the backstack.
Here's an alternative:
val isRootScreen = navController.previousBackStackEntry == null
if you want this is a button so to speak you can have this
yourbutton.setOnClickListener {
val currentFragment = navController.currentDestination?.id
when (navController.graph.startDestination == currentFragment) {
true -> { //Go here}
// Go to the app home
else -> onBackPressed()
}
}

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