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Application resumes failure results with FormsAppCompatActivity

I have a Xamarin Forms app that is currently being created for Android. I have MainActivity that is used to extend FormsApplicationActivity , but since I want to use a custom theme, I had to change it to extend FormsAppCompatActivity (see My other question: Xamarin Forms a custom theme does not work ).

From the moment you switch from FormsApplicationActivity to FormsAppCompatActivity application crashes every time the application is disconnected, and then back to the application. It generates an error in the App.xaml.cs class in the App.xaml.cs method, where I try to install MainPage on a new navigation page:

 protected override void OnResume() { bool isRegistered = _authenticationService.IsRegistered(); MainPage = isRegistered ? new NavigationPage(new LoginPage()) : new NavigationPage(new RegisterPage()); // this results in the crash }

The error I am getting is:

Java.Lang.IllegalStateException: Cannot complete this action after onSaveInstanceState

This is stacktrace:

 03-09 13:43:52.098 I/MonoDroid( 1243): Java.Lang.IllegalStateException: Can not perform this action after onSaveInstanceState 03-09 13:43:52.098 I/MonoDroid( 1243): at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in /Users/builder/data/lanes/2098/3efa14c4/source/mono/external/referencesource/mscorlib/system/runtime/exceptionservices/exceptionservicescommon.cs:143 03-09 13:43:52.098 I/MonoDroid( 1243): at Android.Runtime.JNIEnv.CallIntMethod (IntPtr jobject, IntPtr jmethod) [0x00063] in /Users/builder/data/lanes/2098/3efa14c4/source/monodroid/src/Mono.Android/src/Runtime/JNIEnv.g.cs:386 03-09 13:43:52.098 I/MonoDroid( 1243): at Android.Support.V4.App.FragmentTransactionInvoker.Commit () [0x00033] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer.SwitchContentAsync (Xamarin.Forms.Page view, Boolean animated, Boolean removed, Boolean popToRoot) [0x000e1] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer.OnPushAsync (Xamarin.Forms.Page view, Boolean animated) [0x00000] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer.PushViewAsync (Xamarin.Forms.Page page, Boolean animated) [0x00000] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer.<OnElementChanged>b__13_0 (Xamarin.Forms.Page p) [0x00000] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.EnumerableExtensions.ForEach[T] (IEnumerable`1 enumeration, System.Action`1 action) [0x00010] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.Platform.Android.AppCompat.NavigationPageRenderer.OnElementChanged (Xamarin.Forms.Platform.Android.ElementChangedEventArgs`1 e) [0x001af] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.Platform.Android.VisualElementRenderer`1[TElement].SetElement (Xamarin.Forms.Platform.Android.TElement element) [0x000fc] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.Platform.Android.VisualElementRenderer`1[TElement].Xamarin.Forms.Platform.Android.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) [0x00027] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.Platform.Android.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) [0x0001f] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.Platform.Android.RendererFactory.GetRenderer (Xamarin.Forms.VisualElement view) [0x00000] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.Platform.Android.AppCompat.Platform.AddChild (Xamarin.Forms.Page page, Boolean layout) [0x00015] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.Platform.Android.AppCompat.Platform.SetPage (Xamarin.Forms.Page newRoot) [0x00090] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.Platform.Android.FormsAppCompatActivity.InternalSetPage (Xamarin.Forms.Page page) [0x0001a] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.Platform.Android.FormsAppCompatActivity.AppOnPropertyChanged (System.Object sender, System.ComponentModel.PropertyChangedEventArgs args) [0x0001e] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.BindableObject.OnPropertyChanged (System.String propertyName) [0x00012] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.Application.set_MainPage (Xamarin.Forms.Page value) [0x0008b] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Smartbit.App.OnResume () [0x00020] in C:\Users\leonc\Documents\Visual Studio 2015\Projects\Smartbit\Smartbit\Smartbit\App.xaml.cs:52 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.Application.SendResume () [0x00006] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.Platform.Android.FormsAppCompatActivity.OnStateChanged () [0x00039] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Xamarin.Forms.Platform.Android.FormsAppCompatActivity.OnRestart () [0x00019] in <filename unknown>:0 03-09 13:43:52.098 I/MonoDroid( 1243): at Android.App.Activity.n_OnRestart (IntPtr jnienv, IntPtr native__this) [0x00009] in /Users/builder/data/lanes/2098/3efa14c4/source/monodroid/src/Mono.Android/platforms/android-23/src/generated/Android.App.Activity.cs:4539 03-09 13:43:52.098 I/MonoDroid( 1243): at (wrapper dynamic-method) System.Object:cba7a870-1435-4f70-9059-e10915aba0c0 (intptr,intptr) 03-09 13:43:52.098 I/MonoDroid( 1243): --- End of managed exception stack trace --- 03-09 13:43:52.098 I/MonoDroid( 1243): java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState 03-09 13:43:52.098 I/MonoDroid( 1243): at android.support.v4.app.FragmentManagerImpl.checkStateLoss(FragmentManager.java:1448) 03-09 13:43:52.098 I/MonoDroid( 1243): at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:1466) 03-09 13:43:52.098 I/MonoDroid( 1243): at android.support.v4.app.BackStackRecord.commitInternal(BackStackRecord.java:634) 03-09 13:43:52.098 I/MonoDroid( 1243): at android.support.v4.app.BackStackRecord.commit(BackStackRecord.java:613) 03-09 13:43:52.098 I/MonoDroid( 1243): at md5b60ffeb829f638581ab2bb9b1a7f4f3f.FormsAppCompatActivity.n_onRestart(Native Method) 03-09 13:43:52.098 I/MonoDroid( 1243): at md5b60ffeb829f638581ab2bb9b1a7f4f3f.FormsAppCompatActivity.onRestart(FormsAppCompatActivity.java:86) 03-09 13:43:52.098 I/MonoDroid( 1243): at android.app.Instrumentation.callActivityOnRestart(Instrumentation.java:1181) 03-09 13:43:52.098 I/MonoDroid( 1243): at android.app.Activity.performRestart(Activity.java:5291) 03-09 13:43:52.098 I/MonoDroid( 1243): at android.app.Activity.performResume(Activity.java:5302) 03-09 13:43:52.098 I/MonoDroid( 1243): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2764) 03-09 13:43:52.098 I/MonoDroid( 1243): at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2803) 03-09 13:43:52.098 I/MonoDroid( 1243): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1238) 03-09 13:43:52.098 I/MonoDroid( 1243): at android.os.Handler.dispatchMessage(Handler.java:102) 03-09 13:43:52.098 I/MonoDroid( 1243): at android.os.Looper.loop(Looper.java:136) 03-09 13:43:52.098 I/MonoDroid( 1243): at android.app.ActivityThread.main(ActivityThread.java:5001) 03-09 13:43:52.098 I/MonoDroid( 1243): at java.lang.reflect.Method.invokeNative(Native Method) 03-09 13:43:52.098 I/MonoDroid( 1243): at java.lang.reflect.Method.invoke(Method.java:515) 03-09 13:43:52.098 I/MonoDroid( 1243): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785) 03-09 13:43:52.098 I/MonoDroid( 1243): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601) 03-09 13:43:52.098 I/MonoDroid( 1243): at dalvik.system.NativeStart.main(Native Method)
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2 answers

I solved this by adding a thread to my OnResume method before setting MainPage. Now my OnResume looks like this:

 protected override void OnResume() { base.OnResume(); Task.Delay(10).Wait(); bool isRegistered = _authenticationService.IsRegistered(); MainPage = isRegistered ? new NavigationPage(new LoginPage()) : new NavigationPage(new RegisterPage()); }

See this error report for this workaround.

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I had a similar problem. There are several points to this:

1) Move the MainPage configuration code to the App Designer. Because MainPage must be set in the OnCreate method.

 public App () { MainPage = isRegistered ? new NavigationPage(new LoginPage()) : new NavigationPage(new RegisterPage()); }

2) Before installing OnCreate, you need to install the root page. Since you do not know the page you need, you can simply set the blanc page.

 public App () { MainPage = new ContentPage(); }

3) If this does not help. You can simply add a try / catch block with the abundant MainPage installer. This is a dirty solution, but it works. In AppCompatActivity xamarin uses Fragments not Views. A crash occurs when an android tries to restore a fragment state. On a regular android, we used CommitAllowingStateLoss ().

 try{ MainPage = isRegistered ? new NavigationPage(new LoginPage()) : new NavigationPage(new RegisterPage()); }catch(Exception){}
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