SetWindowThemeWpf: different themes for different windows?

[Rast1234]

Hello. I am trying to open two WPF windows (of the same type) and make them use different themes, to see them live and side by side - this way it's easier to spot style differences. Because applying/comparing themes in design time is not very convenient. I don't really care about style of the window itself, i will be happy to load dark and light style for content.

I can't find a way that, however. My observations:

• SetWindowThemeWpf in window constructor, after InitializeComponent, does nothing visible
• I can omit it entirely and rely only on SetCurrentProcessTheme
• Calling SetWindowThemeWpf as it's suggested in docs, later, eg with a button click, does nothing
• Calling SetCurrentProcessTheme anytime changes the theme for all windows

[Rast1234]

Thanks for the library and write-up of how this all works! Implementing dark mode in WPF is surprisingly difficult, your approach was the only one i was able to fit into my app while understanding what it does

[Aldaviva]

This symptom seems to usually be caused by a missing call to SetCurrentProcessTheme. Can you try calling both SetCurrentProcessTheme (at the top of App.OnStartup) and SetWindowThemeWpf (after Window.InitializeComponent returns)?

I was able to make the WPF demo app show two MainWindow instances in one single process, and each checkbox changes its own window's title bar color independently.

In case it helps, here is the source and binary for the modified WPF demo app with my above changes.

• darknet-demo-wpf.zip

[Rast1234]

Yea, call SetCurrentProcessTheme in the first line of App.OnStartup, and then SetWindowThemeWpf after InitializeComponent. It works as your example: window header changes color, but content style does not. Maybe i am missing something about SkinManager?

[Rast1234]

Looks like it's not possible now:

• EffectiveCurrentProcessThemeIsDarkChanged is fired only for process theme changes
• appResources.Add(_skinResources); is global for app and if you change its source, it gets changed for all windows

I'll try to hack a manager for window scope...

[Aldaviva]

Yeah SkinManager is currently somewhat limited because it's only aware of the process's theme, not each window's effective theme. As you said, it would need to be aware of when the effective window theme changes, and it would need to modify the window's ResourceDictionary, not the app's shared ResourceDictionary. I think I considered adding this functionality in the past, but I ran into some trouble that made it difficult or impossible, and I don't remember exactly what it was.

[Rast1234]

I see that you intentionally stayed away from style management in this project, and i understand why! it must be another level of madness :) Maybe this limitation is worth mentioning in readme?

[Aldaviva]

Yeah the client area can get pretty complex, especially with controls like the WPF DataGrid. But most of all, it's subjective how these controls should look in dark mode, highly dependent on existing app styles, and best left to the developers or their chosen UI libraries (MahApps, Telerik UI, etc) about how it should look, I think.

The SkinManager is definitely a limited example implementation of how to swap resource dictionaries that I added because I realized I was copying common boilerplate between multiple projects. I like your suggestion to clarify its functionality and limitations in the readme and code documentation comments.