IssueTracker

Component used: Activity

Version used: androidx.fragment:fragment-ktx:1.3.0-alpha02

Devices/Android versions reproduced on: Emulator API level 29

When using the Activity Result API in a fragment, it crashes when receiving a result form an activity in a different configuration than when it was launched.  The steps are like this:

1. Launch first activity.
2. Call second activity for result
3. Reorient the device/emulator
4. Finish the second activity (back button)
5. Crash with this stack:

```
2020-03-22 08:55:07.407 6338-6338/my.testapp E/AndroidRuntime: FATAL EXCEPTION: main
    Process: my.testapp, PID: 6338
    java.lang.RuntimeException: Unable to resume activity {my.testapp/my.testapp.activity.main.MainActivity}: java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=0, result=0, data=null} to activity {my.testapp/my.testapp.activity.main.MainActivity}: java.lang.NullPointerException: Attempt to read from field 'androidx.activity.result.ActivityResultCallback androidx.activity.result.ActivityResultRegistry$CallbackAndContract.mCallback' on a null object reference
        at android.app.ActivityThread.performResumeActivity(ActivityThread.java:4205)
        at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:4237)
        at android.app.servertransaction.ResumeActivityItem.execute(ResumeActivityItem.java:52)
        at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:176)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:97)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
     Caused by: java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=0, result=0, data=null} to activity {my.testapp/my.testapp.activity.main.MainActivity}: java.lang.NullPointerException: Attempt to read from field 'androidx.activity.result.ActivityResultCallback androidx.activity.result.ActivityResultRegistry$CallbackAndContract.mCallback' on a null object reference
        at android.app.ActivityThread.deliverResults(ActivityThread.java:4845)
        at android.app.ActivityThread.performResumeActivity(ActivityThread.java:4192)
        at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:4237) 
        at android.app.servertransaction.ResumeActivityItem.execute(ResumeActivityItem.java:52) 
        at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:176) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:97) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:214) 
        at android.app.ActivityThread.main(ActivityThread.java:7356) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 
     Caused by: java.lang.NullPointerException: Attempt to read from field 'androidx.activity.result.ActivityResultCallback androidx.activity.result.ActivityResultRegistry$CallbackAndContract.mCallback' on a null object reference
        at androidx.activity.result.ActivityResultRegistry.doDispatch(ActivityResultRegistry.java:281)
        at androidx.activity.result.ActivityResultRegistry.dispatchResult(ActivityResultRegistry.java:275)
        at androidx.activity.ComponentActivity.onActivityResult(ComponentActivity.java:444)
        at androidx.fragment.app.FragmentActivity.onActivityResult(FragmentActivity.java:181)
        at android.app.Activity.dispatchActivityResult(Activity.java:8110)
        at android.app.ActivityThread.deliverResults(ActivityThread.java:4838)
        at android.app.ActivityThread.performResumeActivity(ActivityThread.java:4192) 
        at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:4237) 
        at android.app.servertransaction.ResumeActivityItem.execute(ResumeActivityItem.java:52) 
        at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:176) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:97) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:214) 
        at android.app.ActivityThread.main(ActivityThread.java:7356) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 
```

There are no problems if there was no configuration change. Also, oddly, there are no problems if there were two configuration changes (e.g. portrait -> landscape -> portrait).

Code for the fragment:

```kotlin
class MainFragment : Fragment() {

    companion object {
        fun newInstance() = MainFragment()
    }

    private val viewModel: MainViewModel by viewModels()

    override fun onCreateView(
            inflater: LayoutInflater,
            container: ViewGroup?,
          savedInstanceState: Bundle?
    ): View {
        val binding = MainFragmentBinding.inflate(inflater, container, false)
        binding.viewModel = viewModel
        binding.lifecycleOwner = viewLifecycleOwner
        return binding.root
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        observeViewModel()
    }

    private fun observeViewModel() {
        // This is just effectively a listener on button press delivered through a BroadcastChannel
        LifecycleChannelListener(viewLifecycleOwner.lifecycle, viewModel.navigateToFirebaseUi) {
            onSignInButtonClicked()
        }
    }

    private val onSignInButtonClicked = prepareCall(StartActivity()) { result ->
        Log.d("@@@@", "R: $result")
    }

    private inner class StartActivity: ActivityResultContract<Unit, Int>() {
        override fun createIntent(input: Unit?): Intent {
            return Intent(requireContext(), MainActivity::class.java)
        }

        override fun parseResult(resultCode: Int, intent: Intent?): Int {
            return 0
        }
    }

}
```