utu:Shadow.Opacity does not support data binding in DataTemplate (Uno.Toolkit.UI)

[HakanL]

Current behavior

When using utu:Shadow.Opacity inside a DataTemplate, binding to a property (e.g., {x:Bind GlowOpacity} or {Binding GlowOpacity}) does not work. The property getter is not called, and the shadow does not appear. However, binding works for other controls (e.g., TextBlock), and hard-coding the value for Opacity works as expected.

Expected behavior

utu:Shadow.Opacity should support data binding in DataTemplates, allowing dynamic shadow opacity per item.

How to reproduce it (as minimally and precisely as possible)

• Clone the minimal repro project: https://github.com/HakanL/UnoToolkitShadowIssue
• Open MainPage.xaml and observe the use of {x:Bind GlowOpacity} and {Binding GlowOpacity} for utu:Shadow.Opacity.
• Run the app. The value is shown in a TextBlock (binding works), but the shadow does not appear unless the value is hard-coded.

Nuget Package:
Uno.Toolkit.UI

Package Version(s): SDK 6.3.28
(latest as of .NET 9, please specify if needed)

Affected platform(s):

• Skia
• WebAssembly
• Android
• iOS
• macOS (AppKit)
• Mac Catalyst
• GTK (Linux)
• Linux Framebuffer
• Tizen
• Windows

IDE:

• Visual Studio 2022

Relevant plugins:
None

Anything else we need to know?

The property getter for the bound value is not called for utu:Shadow.Opacity, but is called for other controls in the same DataTemplate. This suggests a limitation or bug in the Uno.Toolkit Shadow control’s binding support.

[Xiaoy312]

@HakanL

		<DataTemplate x:Key="MenuItemGridViewTemplate" x:DataType="local:Thing">
			<utu:ShadowContainer x:Name="ShadowContainer">
				<utu:ShadowContainer.Shadows>
					<utu:ShadowCollection>
                        <utu:Shadow Opacity="{x:Bind GlowOpacity}" .../>
						<utu:Shadow Opacity="{Binding GlowOpacity}" .../>
						<utu:Shadow Opacity="{Binding ElementName=ShadowContainer, Path=DataContext.GlowOpacity}" .../>

This is an issue with the uno binding, likely it would worked under winappsdk[to confirm].
The problem here is that, at least in the case of uno, the data-context doesnt get propagated into property of UIElement. Thus the first two bindings will fail to resolve. [todo: create/find an uno issue]
As a workaround, you can use a view as a proxy to obtain the data-context, as shown in the last line.

[HakanL]

Using that 3rd binding worked great, thank you! I don't 100% understand why that works but the standard way doesn't, but it's working so that's good! :)