Exception on Dispose

[daveclarke]

I have a button defined in XAML as:

<buttoncircle:CircleButton Grid.Row="8" Grid.Column="1" x:Name="infoButton" Icon="ic_info" TextColor="White" FontSize="24" HeightRequest="24" WidthRequest="24" BorderThickness="1" BackgroundColor="#0076fa" VerticalOptions="Center" HorizontalOptions="Center" Command="{Binding InfoCommand}" />

It displays perfectly and is used to display some information text on a new page. But if I cancel from the page even without tapping the button I get a null reference exception that appears to be an issue triggered by trying to Dispose the button.

at ButtonCircle.FormsPlugin.iOS.ButtonCircleRenderer.OnElementChanged (Xamarin.Forms.Platform.iOS.ElementChangedEventArgs1[TElement] e) [0x00022] in <a4abc774e1e04cf88321114ac113a4d8>:0 at Xamarin.Forms.Platform.iOS.VisualElementRenderer1[TElement].SetElement (TElement element) [0x00118] in :0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer1[TElement].Dispose (System.Boolean disposing) [0x0008c] in <eb211aa32ac8429489411f4d642db9c2>:0 at Xamarin.Forms.Platform.iOS.ViewRenderer2[TView,TNativeView].Dispose (System.Boolean disposing) [0x00000] in :0
at Xamarin.Forms.Platform.iOS.ButtonRenderer.Dispose (System.Boolean disposing) [0x00036] in :0
at Foundation.NSObject.Dispose () [0x00000] in /Users/builder/data/lanes/5520/51128b8c/source/xamarin-macios/src/Foundation/NSObject2.cs:133
at Xamarin.Forms.Platform.iOS.Platform.DisposeModelAndChildrenRenderers (Xamarin.Forms.Element view) [0x00038] in :0
at Xamarin.Forms.Platform.iOS.Platform+d__23.MoveNext () [0x0015f] in :0
--- End of stack trace from previous location where exception was thrown ---

Is there something I'm missing here?

[wilsonvargas]

how do you cancel button? can you show me your code please?

[daveclarke]

I'm not sure I understand the question. I declare the button in xaml. I'm using FreshMvvm framework for the app so when I want to navigate back to the previous page I use:

 await CoreMethods.PopPageModel(data: true, modal: true, animate: true);

I've just checked FreshMvvm source and PopPageModel resolves to

public virtual Task PopPage (bool modal = false, bool animate = true)
    {
        if (modal)
            return Navigation.PopModalAsync (animate);
        return Navigation.PopAsync (animate);
    }

And Navigation.PopModalAsync() is a Xamarin.Forms method. Not sure if that helps.

[daveclarke]

https://bugzilla.xamarin.com/show_bug.cgi?id=21457 is an old reference but may be relevant?

[extraPaul]

I'm getting the same issue. I have a page that has multiple CircleButtons, and when I navigate back to the home page I get a null reference exception. I use Navigation.PopAsync() to go back to the home page. Here is part of the stack trace:

Object reference not set to an instance of an object (System.NullReferenceException)
at ButtonCircle.FormsPlugin.iOS.ButtonCircleRenderer.OnElementChanged (Xamarin.Forms.Platform.iOS.ElementChangedEventArgs1[TElement] e) [0x00022] in <a4abc774e1e04cf88321114ac113a4d8>:0 at Xamarin.Forms.Platform.iOS.VisualElementRenderer1[TElement].SetElement (TElement element) [0x00118] in :0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer1[TElement].Dispose (System.Boolean disposing) [0x0008c] in <eb211aa32ac8429489411f4d642db9c2>:0 at Xamarin.Forms.Platform.iOS.ViewRenderer2[TView,TNativeView].Dispose (System.Boolean disposing) [0x00000] in :0
at Xamarin.Forms.Platform.iOS.ButtonRenderer.Dispose (System.Boolean disposing) [0x00036] in D:\agent_work\1\s\Xamarin.Forms.Platform.iOS\Renderers\ButtonRenderer.cs:48
at Foundation.NSObject.Dispose ()

As mentioned earlier, it seems like the exception is thrown as the button is being disposed.

[wilsonvargas]

Check latest version (1.2.52). I tested this version on an IPhone with iOS 11, Samsung Galaxy S8 with Android 7.1 and in my computer with Windows 10, it's work fine.

Please tell me if you have a issue again.