Navigation DESTINATION_NAME is unknown to this NavController, ReOpening fragment previously closed using navController.popBackStack()?

Question

I am using Navigation Component in my app , recently it was working correctly but after updating project to AndroidX I am getting error navigation destination DESTINATION_NAME is unknown to this NavController only if that destination(Which I'm going to open) is previously closed from itself using navController.popBackStack(). Also, There is no error if I close DESTINATION fragment from MainActivity, But Error only Occurs fragment is closed from itself using popBackStack. like below

DestinationFragment

viewModelOfActivity.handleBackButton.observe(this, Observer {
        Navigation.findNavController(requireActivity(), R.id.main_nav_host).popBackStack() 
        //CALLING popBackStack() HERE CAUSING PROBLEM WHEN REOPNING THIS DESTINATION(or frg ) AGIAN
})  

MainActivity

override fun onBackPressed() {
    if (myViewModel.isDefaultBehaviour.value == true) {
        super.onBackPressed()
    } else{
        myViewModel.handleBackButton.value=true
        //NO ERROR IF HANDLE BACK BUTTON HERE ie->findNavController(R.id.main_nav_host).popBackStack()
       //INSTEAD OF myViewModel.handleBackButton
    }
}

I Have also checked related Question but no help Similar Question.

NOTE: I am using the latest version of the navigation library (alpha05)

Answer 1

I was using SingleLiveEvent in DestinationFragment to observe back press from MainActivity as I have already mentioned this in my question. So the problem was in SingleLiveEvent I noticed that I have accidently changed code of fun observe(owner: LifecycleOwner, observer: Observer<in T>) to

override fun observe(owner: LifecycleOwner, observer: Observer<in T>) {
    super.observe(owner, observer)//Here is problem I was calling super twice in function
    if (hasActiveObservers()) {
        Log.w(TAG, "Multiple observers registered but only one will be notified of changes.")
    }
    super.observe(owner, Observer { t ->/** other code*//})
}

Here you can see I was calling super function twice which calls onChanged of observer twice in Fragment , below code is called twice
Navigation.findNavController(requireActivity(), R.id.main_nav_host).popBackStack() which popBackStack() twice.
Then I have changed observe function like below

@MainThread
override fun observe(owner: LifecycleOwner, observer: Observer<in T>) {
    if (hasActiveObservers()) {
        Log.w(TAG, "Multiple observers registered but only one will be notified of changes.")
    }
    super.observe(owner, Observer { t ->/** other code*//})
}  

Now my code works fine