Xamarin Forms PopAsync crash

Question

I have built a Xamarin forms app with PCL.

The application crashes sometimes on await Navigation.PopAsync(); I have found this https://forums.xamarin.com/discussion/62414/app-resuming-results-in-crash-with-formsappcompatactivity , but it's doesn't help

It appears only on android 5.0 and above. I'm using Xamarin.Forms 2.3.3

Here is crash log:

Xamarin caused by: android.runtime.JavaProxyThrowable: System.AggregateException: A Task's exception(s) were not observed either by Waiting on the Task or accessing its Exception property. As a result, the unobserved exception was rethrown by the finalizer thread. ---> System.AggregateException: One or more errors occurred. ---> Java.Lang.RuntimeException: Can not perform this action after onSaveInstanceState
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at Java.Interop.JniEnvironment+InstanceMethods.CallIntMethod (Java.Interop.JniObjectReference instance, Java.Interop.JniMethodInfo method) [0x00084] in <bd356ef77b9a4127a500b8385b303c4b>:0 
  at Android.Runtime.JNIEnv.CallIntMethod (System.IntPtr jobject, System.IntPtr jmethod) [0x0000e] in <bc38a7e9ac144e5b8f3cbfa1d1cb295b>:0 
  at Android.Support.V4.App.FragmentTransactionInvoker.Commit () [0x00033] in <27c17fe440cf491ba8255bcefade6e02>:0 
  at Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer.SwitchContentAsync (Xamarin.Forms.Page view, System.Boolean animated, System.Boolean removed, System.Boolean popToRoot) [0x0014b] in <651b788f2205433c9db3a98957b5b8aa>:0 
  at Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer.OnPopViewAsync (Xamarin.Forms.Page page, System.Boolean animated) [0x00021] in <651b788f2205433c9db3a98957b5b8aa>:0 
  at Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer.PopViewAsync (Xamarin.Forms.Page page, System.Boolean animated) [0x00000] in <651b788f2205433c9db3a98957b5b8aa>:0 
  at Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer.OnPopped (System.Object sender, Xamarin.Forms.Internals.NavigationRequestedEventArgs e) [0x0000e] in <651b788f2205433c9db3a98957b5b8aa>:0 
  at Xamarin.Forms.NavigationPage+<Xamarin-Forms-INavigationPageController-PopAsyncInner>d__63.MoveNext () [0x0006e] in <83d3340f3b274d389854ce45f51043f6>:0 
--- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0004e] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at Xamarin.Forms.NavigationPage+<PopAsync>d__38.MoveNext () [0x001b9] in <83d3340f3b274d389854ce45f51043f6>:0 
   --- End of inner exception stack trace ---
  at Xamarin.Forms.NavigationPage+<>c.<SafePop>b__93_0 (System.Threading.Tasks.Task`1[TResult] t) [0x0000e] in <83d3340f3b274d389854ce45f51043f6>:0 
  at System.Threading.Tasks.ContinuationTaskFromResultTask`1[TAntecedentResult].InnerInvoke () [0x00027] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at System.Threading.Tasks.Task.Execute () [0x00016] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
   --- End of inner exception stack trace ---
---> (Inner Exception #0) System.AggregateException: One or more errors occurred. ---> Java.Lang.RuntimeException: Can not perform this action after onSaveInstanceState
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at Java.Interop.JniEnvironment+InstanceMethods.CallIntMethod (Java.Interop.JniObjectReference instance, Java.Interop.JniMethodInfo method) [0x00084] in <bd356ef77b9a4127a500b8385b303c4b>:0 
  at Android.Runtime.JNIEnv.CallIntMethod (System.IntPtr jobject, System.IntPtr jmethod) [0x0000e] in <bc38a7e9ac144e5b8f3cbfa1d1cb295b>:0 
  at Android.Support.V4.App.FragmentTransactionInvoker.Commit () [0x00033] in <27c17fe440cf491ba8255bcefade6e02>:0 
  at Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer.SwitchContentAsync (Xamarin.Forms.Page view, System.Boolean animated, System.Boolean removed, System.Boolean popToRoot) [0x0014b] in <651b788f2205433c9db3a98957b5b8aa>:0 
  at Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer.OnPopViewAsync (Xamarin.Forms.Page page, System.Boolean animated) [0x00021] in <651b788f2205433c9db3a98957b5b8aa>:0 
  at Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer.PopViewAsync (Xamarin.Forms.Page page, System.Boolean animated) [0x00000] in <651b788f2205433c9db3a98957b5b8aa>:0 
  at Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer.OnPopped (System.Object sender, Xamarin.Forms.Internals.NavigationRequestedEventArgs e) [0x0000e] in <651b788f2205433c9db3a98957b5b8aa>:0 
  at Xamarin.Forms.NavigationPage+<Xamarin-Forms-INavigationPageController-PopAsyncInner>d__63.MoveNext () [0x0006e] in <83d3340f3b274d389854ce45f51043f6>:0 
--- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0004e] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at Xamarin.Forms.NavigationPage+<PopAsync>d__38.MoveNext () [0x001b9] in <83d3340f3b274d389854ce45f51043f6>:0 
   --- End of inner exception stack trace ---
  at Xamarin.Forms.NavigationPage+<>c.<SafePop>b__93_0 (System.Threading.Tasks.Task`1[TResult] t) [0x0000e] in <83d3340f3b274d389854ce45f51043f6>:0 
  at System.Threading.Tasks.ContinuationTaskFromResultTask`1[TAntecedentResult].InnerInvoke () [0x00027] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at System.Threading.Tasks.Task.Execute () [0x00016] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
---> (Inner Exception #0) Java.Lang.RuntimeException: Can not perform this action after onSaveInstanceState
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at Java.Interop.JniEnvironment+InstanceMethods.CallIntMethod (Java.Interop.JniObjectReference instance, Java.Interop.JniMethodInfo method) [0x00084] in <bd356ef77b9a4127a500b8385b303c4b>:0 
  at Android.Runtime.JNIEnv.CallIntMethod (System.IntPtr jobject, System.IntPtr jmethod) [0x0000e] in <bc38a7e9ac144e5b8f3cbfa1d1cb295b>:0 
  at Android.Support.V4.App.FragmentTransactionInvoker.Commit () [0x00033] in <27c17fe440cf491ba8255bcefade6e02>:0 
  at Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer.SwitchContentAsync (Xamarin.Forms.Page view, System.Boolean animated, System.Boolean removed, System.Boolean popToRoot) [0x0014b] in <651b788f2205433c9db3a98957b5b8aa>:0 
  at Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer.OnPopViewAsync (Xamarin.Forms.Page page, System.Boolean animated) [0x00021] in <651b788f2205433c9db3a98957b5b8aa>:0 
  at Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer.PopViewAsync (Xamarin.Forms.Page page, System.Boolean animated) [0x00000] in <651b788f2205433c9db3a98957b5b8aa>:0 
  at Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer.OnPopped (System.Object sender, Xamarin.Forms.Internals.NavigationRequestedEventArgs e) [0x0000e] in <651b788f2205433c9db3a98957b5b8aa>:0 
  at Xamarin.Forms.NavigationPage+<Xamarin-Forms-INavigationPageController-PopAsyncInner>d__63.MoveNext () [0x0006e] in <83d3340f3b274d389854ce45f51043f6>:0 
--- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0004e] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] in <7f637a73ebd0402caa24252e5f30bf7b>:0 
  at Xamarin.Forms.NavigationPage+<PopAsync>d__38.MoveNext () [0x001b9] in <83d3340f3b274d389854ce45f51043f6>:0 
  --- End of managed Java.Lang.RuntimeException stack trace ---
java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState
    at android.support.v4.app.FragmentManagerImpl.checkStateLoss(FragmentManager.java:1493)
    at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:1511)
    at android.support.v4.app.BackStackRecord.commitInternal(BackStackRecord.java:638)
    at android.support.v4.app.BackStackRecord.commit(BackStackRecord.java:617)
    at md5b60ffeb829f638581ab2bb9b1a7f4f3f.FormsAppCompatActivity.n_onBackPressed(Native Method)
    at md5b60ffeb829f638581ab2bb9b1a7f4f3f.FormsAppCompatActivity.onBackPressed(FormsAppCompatActivity.java:40)
    at android.app.Activity.onKeyUp(Activity.java:2713)
    at android.view.KeyEvent.dispatch(KeyEvent.java:3280)
    at android.app.Activity.dispatchKeyEvent(Activity.java:2983)
    at android.support.v7.app.AppCompatActivity.dispatchKeyEvent(AppCompatActivity.java:524)
    at android.support.v7.view.WindowCallbackWrapper.dispatchKeyEvent(WindowCallbackWrapper.java:50)
    at android.support.v7.app.AppCompatDelegateImplBase$AppCompatWindowCallbackBase.dispatchKeyEvent(AppCompatDelegateImplBase.java:241)
    at android.support.v7.view.WindowCallbackWrapper.dispatchKeyEvent(WindowCallbackWrapper.java:50)
    at com.android.internal.policy.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:2689)
    at android.view.ViewRootImpl$ViewPostImeInputStage.processKeyEvent(ViewRootImpl.java:5233)
    at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:5186)
    at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4633)
    at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4686)
    at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4652)
    at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4794)
    at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4660)
    at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:4851)
    at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4633)
    at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4686)
    at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4652)
    at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4660)
    at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4633)
    at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4686)
    at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4652)
    at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4827)
    at android.view.ViewRootImpl$ImeInputStage.onFinishedInputEvent(ViewRootImpl.java:5070)
    at android.view.inputmethod.InputMethodManager$PendingEvent.run(InputMethodManager.java:2877)
    at android.view.inputmethod.InputMethodManager.invokeFinishedInputEventCallback(InputMethodManager.java:2449)
    at android.view.inputmethod.InputMethodManager.finishedInputEvent(InputMethodManager.java:2440)
    at android.view.inputmethod.InputMethodManager$ImeInputEventSender.onInputEventFinished(InputMethodManager.java:2854)
    at android.view.InputEventSender.dispatchInputEventFinished(InputEventSender.java:141)
    at android.os.MessageQueue.nativePollOnce(Native Method)
    at android.os.MessageQueue.next(MessageQueue.java:323)
    at android.os.Looper.loop(Looper.java:143)
    at android.app.ActivityThread.main(ActivityThread.java:7230)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

Answer 1

Because the FormsAppCompatActivity

didn't allow your code to manipulate the page diplaying...

That's all. I've searched a lot, and no choice for this moment. Maybe it's a bug, anyway we had right of Push, so would that. But it wouldn't. Solution I choosed was:

1. find out the target page from the history
2. remove it from the NavigationStack, in order to push it back to the top of the NavigationStack
3. then I could cut off the wanted pages of the NavigationStack

Answer 2

The first row is saying your task crashed so your app crashed. Adding this class

public static class LogException
{
    public static void LogExceptions(this Task task)
    {
        task.ContinueWith(t =>
        {
            var aggException = t.Exception.Flatten();
            foreach (var exception in aggException.InnerExceptions)
            {
                System.Diagnostics.Debug.WriteLine("LOG EXCEPTION catch: " + exception);
            }
        },
        TaskContinuationOptions.OnlyOnFaulted);
    }
}

and using it like this:

Task.Factory.StartNew(() => PopYourPage()).LogExceptions();

would catch these exceptions not killing your app. What are you popping, can you explain it better?