WinUI - TemplateBinding not working for Commands

[DRAirey1]

Describe the bug

TemplateBinding to an ICommand property doesn't work in WinUI. However, explicitly binding using the RelativeSource does.
BgLabelControlApp.zip
This doesn't work:

<ResourceDictionary xmlns:local="using:ClassLibrary1"
					xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
	<Style TargetType="local:BgLabelControl">
		<Setter Property="Template">
			<Setter.Value>
				<ControlTemplate TargetType="local:BgLabelControl">
					<Grid Background="{TemplateBinding Background}"
						  Height="100"
						  Width="100">
						<Button Content="{TemplateBinding Label}"
								HorizontalAlignment="Center"
                                Command="{TemplateBinding GoBack}"
					</Grid>
				</ControlTemplate>
			</Setter.Value>
		</Setter>
	</Style>
</ResourceDictionary>

This works:

<ResourceDictionary xmlns:local="using:ClassLibrary1"
					xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
	<Style TargetType="local:BgLabelControl">
		<Setter Property="Template">
			<Setter.Value>
				<ControlTemplate TargetType="local:BgLabelControl">
					<Grid Background="{TemplateBinding Background}"
						  Height="100"
						  Width="100">
						<Button Content="{TemplateBinding Label}"
								HorizontalAlignment="Center"
                                Command="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=GoBack, Mode=OneWay}"
								VerticalAlignment="Center"/>
					</Grid>
				</ControlTemplate>
			</Setter.Value>
		</Setter>
	</Style>
</ResourceDictionary>

Steps to reproduce the bug

1. Expand the attached zip file.
2. Run the application. The second button doesn't work
3. Replace the TemplateBinding with "{Binding RelativeSource={RelativeSource TemplatedParent}, Path=GoBack, Mode=OneWay}"
4. Run the application. The second button works.

Expected behavior

One expects TemplateBinding to bind to the templated parent.

Screenshots

No response

NuGet package version

No response

Windows app type

• UWP
• Win32

Device form factor

Desktop

Windows version

Windows 11 (21H2): Build 22000

Additional context

No response

[MikeHillberg]

{TemplateBinding} only supports binding to a property that's backed by a DependencyProperty, which could be causing this. {Binding} uses reflection and generated code-behind to bind to any WinRT or C# property.

[DRAirey1]

Did you look at the code? What makes you think it's not binding to a DependencyProperty?

[kmgallahan]

Dupe of #4546 ?

[DRAirey1]

Yeah, it's likely. The notes say that someone's having trouble with the repro, so the ZIP file here is an easy way to validate that you have a real bug.

[MikeHillberg]

Did you look at the code? What makes you think it's not binding to a DependencyProperty?

Sorry, I was looking at the code in the Issue and didn't notice the zip file link. Thanks for the repro.

[kmgallahan]

May also be related to #2508 in that x:Bind behevior in templates & resource dictionaries is finicky, failing there when:

x:Bind to a property outside the data template works fine ✅
x:Bind to that same property but with function binding fails to build ❌
x:Bind to that same property from a visual state setter crashes at runtime ❌
x:Bind to that same property with a converter crashes at runtime ❌

[DRAirey1]

May also be related to #2508 in that x:Bind behavior in templates & resource dictionaries is finicky, failing there when:

No. x:Bind is done in code behind. This is not code-behind related code. Definitely related to #4546

[Panda-Sharp]

Just started to play with WinUI, I started with 1.2, and I just hit this issue #4546

[andreaslennartz]

Just stumbled across this exact same issue when creating a very simple CustomControl.

Can confirm that this is still a thing in 1. Template binding works properly for all other properties, but for some reason it doesn't work with commands. The mentioned workaround (Replace {TemplateBinding GoBack} with {Binding RelativeSource={RelativeSource TemplatedParent}, Path=GoBack, Mode=OneWay}) works.

The solution is simple, but took me a while to find this - and to me this a very annoying bug. Should have a higher priority. Hope this can get fixed soon!