onCleared is not being called on Fragment's attached ViewModel

Question

I stumbled on a problem when ViewModel.OnCleared() is not being called when the app goes to background (even if Don't keep activities is enabled) but I can see that Fragment.onDestroy() is actually being called.

What could be wrong in the following code? How can I make ViewModel.OnCleared() to be actually called in this scenario?

ViewModel:

class ViewModelFirst(application: Application) : AndroidViewModel(application) {

    companion object {
        private const val TAG = "ViewModelFirst"
    }

    init {
        Log.v(TAG, "Created")
    }

    override fun onCleared() {
        super.onCleared()
        Log.v(TAG, "onCleared")
    }
}

Fragment:

class FragmentFirst : Fragment() {

    companion object {
        private const val TAG = "FragmentFirst"
    }

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {

        ViewModelProviders.of(this).get(ViewModelFirst::class.java)

        return inflater.inflate(R.layout.fragment_first, container, false)
    }

    override fun onDestroy() {
        super.onDestroy()
        Log.v(TAG, "onDestroy")
    }
}

Activity:

class MainActivity : AppCompatActivity() {

    companion object {
        private const val TAG = "MainActivity"
    }
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        if (savedInstanceState == null) {
            supportFragmentManager.beginTransaction().replace(R.id.container, FragmentFirst()).commit()
        }
    }

    override fun onDestroy() {
        super.onDestroy()
        Log.v(TAG, "onDestroy")
    }    
}

Answer myself:

It's a bug of com.android.support:appcompat-v7:27.1.0

I am experiencing this issue if I use the following dependencies:

implementation 'com.android.support:appcompat-v7:27.1.0'
implementation "android.arch.lifecycle:extensions:1.1.0"

If I change the version of appcompat-v7 27.1.0 -> 27.0.2, then ViewModel.OnCleared()works as expected (I have the call when the app goes to background).

appcompat-v7:28.0.0-alpha1 works as well, looks like this is a problem only of appcompat-v7:27.1.0

Update (June 2018)

As @Akshay said, the bug was kinda fixed on 27.1.1. But not fully unfortunately.

The following scenario is still unfixed:

1. Have Don't keep activities enabled.
2. Start the app.
3. Push home button.

On 27.0.2 I have the following output at logcat:

V/ViewModelFirst: Created
V/ViewModelFirst: onCleared
V/FragmentFirst: onDestroy
V/MainActivity: onDestroy

Which totally correct.

But on 27.1.1 till 28.0.0-alpha3 I have the following output at logcat:

V/ViewModelFirst: Created
V/FragmentFirst: onDestroy
V/MainActivity: onDestroy

As we can see activity and fragment was destroyed but viewModel was not notified with onCleared.

I suspect that in case if the Don't keep activities will be disabled and the app at background will be naturally unloaded by Android (due another app claiming for a bunch of resources) at some moment of time the viewModel.onCleared() will not be called which is very sad.

P.S. I have pushed the code here: https://github.com/allco/onClearedInvestigation

And have reported the issue to Google here: https://issuetracker.google.com/issues/110285295

Update (August 2018)

28.0.0-rc01 has this problem solved. Yay!

Answer 1

It was an issue in Support Library v27.1.0 and has been fixed in Support Library v27.1.1.

There is a bug reported previously at https://issuetracker.google.com/issues/74139250.

Refer this link for more details: https://developer.android.com/topic/libraries/support-library/revisions