x:Bind to ActualTheme does not update when the control's theme actually changes

[HO-COOH]

Describe the bug

Continue from #10389 , when x:Bind to a UserControl.ActualTheme actually compiles, it does not trigger update when the theme actually changes.

Steps to reproduce the bug

1. Create a new C++ project
2. Create a new UserControl called MyControl
3. Use this xaml

    <StackPanel>
        <local:MyControl x:Name="MyControl" />
        <TextBlock Text="{x:Bind local:MyPage.ElementThemeToString(MyControl.ActualTheme), Mode=OneWay}" />
    </StackPanel>

4. Build and run, switch theme in windows settings, the text is not updated.

Expected behavior

No response

Screenshots

NuGet package version

None

Windows version

No response

Additional context

Repro

[AndrewKeepCoding]

UserControl's ActualTheme is not a DependencyProperty.

You can use the ActualThemeChanged to get notified when control's theme is changed.

public SomeUserControl()
{
    this.InitializeComponent();
    ActualThemeChanged += SomeUserControl_ActualThemeChanged;
}

private void SomeUserControl_ActualThemeChanged(FrameworkElement sender, object args)
{
    var actualTheme = sender.ActualTheme;
}

Or even go further and add a DependencyProperty to your UserControl and apply the changes in SomeUserControl_ActualThemeChanged.

[HO-COOH]

UserControl's ActualTheme is not a DependencyProperty.

@AndrewKeepCoding How?

[AndrewKeepCoding]

Oops. You are right. It is a DependencyProperty.

[snigdha011997]

Hi @HO-COOH , can you please add a minimal repro project for the issue?

[HO-COOH]

Hi @HO-COOH , can you please add a minimal repro project for the issue?

I literally included a repro in OP Additional context section.