Window does not apply implicit Window styles

[dotMorten]

Description

If I define an implicit style for a Window in App.xaml.cs, this style will never get applied. You're forced to explicitly set the style on every single window instance.

Reproduction Steps

1. Create a new WPF application.
2. Add the following style to App.xaml.cs:

    <Application.Resources>

        <Style TargetType="Window" x:Key="DefaultWindowStyle">
            <Setter Property="Background" Value="Red" />
        </Style>

        <Style BasedOn="{StaticResource DefaultWindowStyle}" TargetType="Window" />

    </Application.Resources>

3. Run the application and notice the Window doesn't have a red Background.
4. In MainWindow.xaml set the Window style explicitly by adding Style="{StaticResource DefaultWindowStyle}"
5. Notice the window now has a red background.

Expected behavior

Implicit styles should also be applied to Window instances.

Actual behavior

Implicit styles do not apply to Window instances.

Regression?

No response

Known Workarounds

No known workaround for implicit styles - only explicit styles work.

Impact

Harder to maintain consistent look and feel of windows, or to create styling libraries that doesn't require extra code on every single window instance.

Configuration

.NET 9.0.101
Windows 11 23H2, x64

Other information

No response

[dipeshmsft]

@dotMorten, we got into this but later found out that this was by design.

Implicit styles are applied to the exact type as defined in the TargetType of the style. They are not applied to derived classes.

Now, as MainWindow is subclassed from Window, therefore the implicit styles don't get applied to MainWindow.

[dotMorten]

That’s not quite true though. If you create a style for ButtonBase it is also applied to both Button and ToggleButton sub classes. Why is Window any different?