BoxView.BackgroundColor binding does not work on WPF

[domyd]

Description

BoxView.BackgroundColor does not update when bound to a Xamarin.Forms.Color ViewModel property on WPF. It does use the inital value of the property to set its background color, but does not react to changes of the property.

Related issue: #4338

Steps to Reproduce

1. Download and open repro
2. Start the WPF application
3. Click the "Switch" button

Expected Behavior

The BoxView's color should change.

Actual Behavior

The BoxView's color does not change.

Additional Info

The BoxView.Color property works as expected and could be considered a valid workaround as I did not yet come across a situation where BoxView.Color behaves differently than BoxView.BackgroundColor. In MainPage.xaml, there's a commented-out BoxView that binds the color to BoxView.Color, which works as expected.

<!--  this works  -->
<!--<BoxView
    HeightRequest="100"
    WidthRequest="100"
    Color="{Binding Color}" />-->
<!--  this does not  -->
<BoxView
    BackgroundColor="{Binding Color}"
    HeightRequest="100"
    WidthRequest="100" />

Basic Information

• Version with issue: Latest stable (3.4.0.1008975) and latest prerelease (4.0.0.8055-pre1)
• IDE: Visual Studio 15.9.4
• Platform Target Frameworks:
  • WPF: .NET Framework 4.7.1
• Nuget Packages: None

Reproduction Link

BgBoxViewBindingIssue.zip

[jfversluis]

Hm! Funny! It seems that Color is actually the designed way of setting the (background)color. The BackgroundColor is actually there by inheritance from VisualElement. Depending on the platform implementation I see a mix of Color and BackgroundColor going on.

Did you test this on any other platforms?

On WPF it seems that the color change is only fired for Color in OnElementChanged so that explains why the initial color sticks, but nothing after that (https://github.com/xamarin/Xamarin.Forms/blob/master/Xamarin.Forms.Platform.WPF/Renderers/BoxViewRenderer.cs#L44). But it looks like it is a good idea to unify all this across all platforms and eliminate the ambiguity between Color and BackgroundColor

[charlesroddie]

I suspect this has nothing to do with binding and that even if the BackgroundColor property is updated, the colour does not change.