IssueTracker

Artifact used:
com.android.support:appcompat-v7

Version used:
28.0.0-alpha3, 28.0.0-alpha1, 27.1.1

- Relevant code to trigger the issue:

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")
    }

    fun onStartClicked(view: View) {
        supportFragmentManager
            .beginTransaction()
            .replace(R.id.container, FragmentSecond())
            .addToBackStack("second")
            .commit()
    }
}

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")
    }
}


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")
    }
}

The test project is here:  https://github.com/allco/onClearedInvestigation

Steps to reproduce:

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


Expected behaviour is the following output at logcat:
V/ViewModelFirst: Created
V/ViewModelFirst: onCleared
V/FragmentFirst: onDestroy
V/MainActivity: onDestroy

This is how it exactly works on 27.0.2.



Real behaviour is the following output at logcat:
V/ViewModelFirst: Created
V/FragmentFirst: onDestroy
V/MainActivity: onDestroy

This is how it works on all the released versions of support library starting from  27.1.1 and till  28.0.0-alpha3

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

I suspect that if in case the "Don't keep activities" is disabled and the app at background is being unloaded by Android at some moment of time "viewModel.onCleared()" will not be called which is incorrect behaviour.