[Bug] NullException at iOS.Effects.iOSViewStyleEffect.OnDetached

[NickeManarin]

Platform:

• OS: iOS
• Device: iPhoneSimulator
• Sdk version: iOS 12.2
• Xamarin.Forms: 4.1.0.581479

Describe the bug
I'm getting a NullException when navigating backwards (to a previous page).
I don't remember ever using that iOSViewStyleEffect, so I have no control over it.

View or View.Layer may be null in here:

Sharpnado.Presentation.Forms/Sharpnado.Presentation.Forms.iOS/Effects/ViewStyleEffect .cs

Line 62 in 71b1ab7

view.Layer.MasksToBounds = _DefaultMaskToBounds;

To Reproduce
Steps to reproduce the behavior:

1. Run the test project.
2. Click on Test
3. Click on Back
4. See error

Exceptions

System.NullReferenceException: Object reference not set to an instance of an object
  at Sharpnado.Presentation.Forms.iOS.Effects.iOSViewStyleEffect.OnDetached () [0x0001c] in <ec6c6356fc024ba987678ca56d694c54>:0
  at Xamarin.Forms.Effect.SendDetached () [0x00009] in D:\a\1\s\Xamarin.Forms.Core\Effect.cs:62
  at Xamarin.Forms.PlatformEffect`2[TContainer,TControl].SendDetached () [0x00000] in D:\a\1\s\Xamarin.Forms.Core\PlatformEffect.cs:23
  at Xamarin.Forms.Element.set_EffectControlProvider (Xamarin.Forms.IEffectControlProvider value) [0x0002e] in D:\a\1\s\Xamarin.Forms.Core\Element.cs:238
  at Xamarin.Forms.Platform.iOS.EffectUtilities.RegisterEffectControlProvider (Xamarin.Forms.IEffectControlProvider self, Xamarin.Forms.IElementController oldElement, Xamarin.Forms.IElementController newElement) [0x0000e] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].SetElement (TElement element) [0x00144] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].Dispose (System.Boolean disposing) [0x0008c] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Xamarin.Forms.Platform.iOS.ViewRenderer`2[TView,TNativeView].Dispose (System.Boolean disposing) [0x0005c] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Xamarin.Forms.Platform.iOS.ButtonRenderer.Dispose (System.Boolean disposing) [0x00064] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Foundation.NSObject.Dispose () [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.10.0.157/src/Xamarin.iOS/Foundation/NSObject2.cs:147
  at Xamarin.Forms.Platform.iOS.VisualElementPackager.Dispose (System.Boolean disposing) [0x0003f] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Xamarin.Forms.Platform.iOS.VisualElementPackager.Dispose () [0x00000] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].Dispose (System.Boolean disposing) [0x00058] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Foundation.NSObject.Dispose () [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.10.0.157/src/Xamarin.iOS/Foundation/NSObject2.cs:147
  at Xamarin.Forms.Platform.iOS.VisualElementPackager.Dispose (System.Boolean disposing) [0x0003f] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Xamarin.Forms.Platform.iOS.VisualElementPackager.Dispose () [0x00000] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].Dispose (System.Boolean disposing) [0x00058] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Foundation.NSObject.Dispose () [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.10.0.157/src/Xamarin.iOS/Foundation/NSObject2.cs:147
  at Xamarin.Forms.Platform.iOS.VisualElementPackager.Dispose (System.Boolean disposing) [0x0003f] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Xamarin.Forms.Platform.iOS.VisualElementPackager.Dispose () [0x00000] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].Dispose (System.Boolean disposing) [0x00058] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Foundation.NSObject.Dispose () [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.10.0.157/src/Xamarin.iOS/Foundation/NSObject2.cs:147
  at Xamarin.Forms.Platform.iOS.VisualElementPackager.Dispose (System.Boolean disposing) [0x0003f] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Xamarin.Forms.Platform.iOS.VisualElementPackager.Dispose () [0x00000] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].Dispose (System.Boolean disposing) [0x00058] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Foundation.NSObject.Dispose () [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.10.0.157/src/Xamarin.iOS/Foundation/NSObject2.cs:147
  at Xamarin.Forms.Platform.iOS.VisualElementPackager.Dispose (System.Boolean disposing) [0x0003f] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Xamarin.Forms.Platform.iOS.VisualElementPackager.Dispose () [0x00000] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Xamarin.Forms.Platform.iOS.PageRenderer.Dispose (System.Boolean disposing) [0x00070] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Foundation.NSObject.Dispose () [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.10.0.157/src/Xamarin.iOS/Foundation/NSObject2.cs:147
  at Xamarin.Forms.Platform.iOS.DisposeHelpers.DisposeModalAndChildRenderers (Xamarin.Forms.Element view) [0x00041] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Xamarin.Forms.Platform.iOS.Platform.Xamarin.Forms.INavigation.PopModalAsync (System.Boolean animated) [0x00143] in <0da03a4594684a9bbf17d4a99d39fbc2>:0
  at Xamarin.Forms.Application+NavigationImpl.OnPopModal (System.Boolean animated) [0x0005d] in D:\a\1\s\Xamarin.Forms.Core\Application.cs:380
  at TestApp.Helpers.NavigationHelper.GoBackAsync (System.Boolean animated) [0x00030] in /Users/development/Projects/Xamarin.Demos2/TestApp/Helpers/NavigationHelper.cs:74
  at TestApp.ViewModel.SignUpViewModel.Back_Executed () [0x000b6] in /Users/development/Projects/Xamarin.Demos2/TestApp/ViewModel/SignUpViewModel.cs:114
  at TestApp.ViewModel.SignUpViewModel.<.ctor>b__24_0 () [0x0001f] in /Users/development/Projects/Xamarin.Demos2/TestApp/ViewModel/SignUpViewModel.cs:32
  at System.Runtime.CompilerServices.AsyncMethodBuilderCore+<>c.<ThrowAsync>b__6_0 (System.Object state) [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.10.0.157/src/Xamarin.iOS/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/AsyncMethodBuilder.cs:1023
  at Foundation.NSAsyncSynchronizationContextDispatcher.Apply () [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.10.0.157/src/Xamarin.iOS/Foundation/NSAction.cs:178
  at at (wrapper managed-to-native) UIKit.UIApplication.UIApplicationMain(int,string[],intptr,intptr)
  at UIKit.UIApplication.Main (System.String[] args, System.IntPtr principal, System.IntPtr delegate) [0x00005] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.10.0.157/src/Xamarin.iOS/UIKit/UIApplication.cs:86
  at UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x0000e] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.10.0.157/src/Xamarin.iOS/UIKit/UIApplication.cs:65
  at TestApp.iOS.Application.Main (System.String[] args) [0x00001] in /Users/development/Projects/Xamarin.Demos2/TestApp.iOS/Main.cs:17

Test project

https://github.com/NickeManarin/Xamarin.Demos2

[roubachof]

yup I will make some cleanup during august, and pull the effects out of the project (I use mrxten ripple effects).

[NickeManarin]

Ok, is there anything that I can do to mitigate this issue while it's not fixed?
I can't continue testing my iOS project because of it.

[roubachof]

Don't think so, I won't release something new before the end of august.
What I always do for such case, is fork and wait next release :)