Mahapps.metro: The window background is not shown correctly in the designer

[timunie]

Describe the bug

If one designs a MetroWindow in the Visual Studios designer it is not shown correctly. It is shown correctly at runtime. This issue is more visible if one uses the dark theme

Steps to reproduce

1. Create a blank App with MahApps.Metro imported
2. Set the theme to dark
3. Create a new MetroWindow
4. You will notice that the Background is white

Expected behavior

MetroWindow should render the Background correctly. It does if one sets the Background explicitly in XAML

Sample

see https://github.com/Volmancer/OWGENC

Environment

MahApps.Metro version: v2.0.0 v2.1.0 tested
Windows build number: Win10 and Win7 tested
Visual Studio: 2019 16.6.3
Target Framework: .Net Core 3.1 (v4.5.2, v4.7.2)

Screenshots

Designer

Runtime

[punker76]

This seems to be fixed.

Tested with

Microsoft Visual Studio Enterprise 2019
Version 16.6.3

and

Microsoft Visual Studio Enterprise 2019 Preview
Version 16.7.0 Preview 3.1

[timunie]

@punker76 yes, with this line:

If you are not using this line, it does not work. But I know it seems to be a VS issue.

[timunie]

I'll double check this issue in the upcomming v16.7 release of VS and see if it is fixed there.

[punker76]

Oh yeah, I didn't noticed that the Background was set explicitly. Doesn't work in preview. But it's not a MahApps issue, it should be delegate to VS team.

[timunie]

Created an issue at VS: https://developercommunity.visualstudio.com/content/problem/1106526/wpf-designer-the-window-background-is-not-shown-co.html

The more people vote for it, the better the chance that MS looks for it.

[punker76]

(Closed - Not a Bug) Here is the answer from Microsoft: https://developercommunity2.visualstudio.com/t/wpf-designer-the-window-background-is-not-shown-co/1106526#T-N1239787

This is a limitiation of the designer. The designer does not instantiate the real Window MainWindow. It can’t because the designer process has his own window in order to display the content. This is known XAML designer limitation, Repro class hierarchy is:
MainWindow > MetroWindow (from MashApp SDK) > Window (from WPF).
Then in XAML:

Designer cannot create any Window-derived class. So we end up massaging XAML to be:
<_0:StandInWindow />
As a result we lose MetroWindow default style (see https://github.com/MahApps/MahApps.Metro/blob/develop/src/MahApps.Metro/Themes/MetroWindow.xaml).

If you’re using the XAML Designer for .NetCore, you’ll be able to see d:Background on the Window and setting a design-time background color.