ThemeManager.ChangeAppStyle from separate thread doesn't take effect every 4th time

[Dimigergo]

Hello!

When I call ThemeManager.ChangeAppStyle from a separate thread the application style is not changed every 4th time, and ThemeManager.IsThemeChanged is not called.

I have a small example to reproduce this issue.
[https://github.com/Dimigergo/MahappsThemeManager]

There is a log file, called "valami.log" which contains:

2017.05.22. 12:43:29 - Changing theme to Red
2017.05.22. 12:43:29 - Change theme: NewTheme: Red Theme changed.
2017.05.22. 12:43:34 - Changing theme to Amber
2017.05.22. 12:43:34 - Current theme from args: Amber
2017.05.22. 12:43:34 - Current theme from detection: Amber
2017.05.22. 12:43:34 - Change theme: NewTheme: Amber Theme changed.
2017.05.22. 12:43:39 - Changing theme to Emerald
2017.05.22. 12:43:39 - Current theme from args: Emerald
2017.05.22. 12:43:39 - Current theme from detection: Emerald
2017.05.22. 12:43:39 - Change theme: NewTheme: Emerald Theme changed.
2017.05.22. 12:43:44 - Changing theme to Red
2017.05.22. 12:43:44 - Current theme from args: Red
2017.05.22. 12:43:44 - Current theme from detection: Amber
2017.05.22. 12:43:44 - Change theme: NewTheme: Red Theme changed.
2017.05.22. 12:43:49 - Changing theme to Amber
2017.05.22. 12:43:49 - Change theme: NewTheme: Amber Theme changed.
2017.05.22. 12:43:54 - Changing theme to Emerald
2017.05.22. 12:43:54 - Current theme from args: Emerald
2017.05.22. 12:43:54 - Current theme from detection: Emerald
2017.05.22. 12:43:54 - Change theme: NewTheme: Emerald Theme changed.

When Current theme from args and Current theme from detection are appeared, the accent of the application is ok.

Environment:
Mahapps.Metro 1.5.0.23
Windows 8.1 64bit
Visual Studio 2015 Update 3
.NET Framework 4.5.1 - 4.6.1

Thanks in advance!

[batzen]

As i just ported ThemeManager to Fluent.Ribbon i will have a look at this issue.

[batzen]

Ok, this is partially cause by a mistake you made and a "bug" in ThemeManager.

You add all themes you use in App.xaml whereas you only should add one. If you only add one, the issue is gone.

This kind of issue is caused because ThemeManager does not search through the merged dictionaries like wpf does. Which means that wpf searches/applies them in reverse order which means that the last dictionary you merge wins. ThemeManager does not apply this reversed order.
This was the first thing i changed when i ported ThemeManager to Fluent.Ribbon and i will bring those fixes to MahApps in the near future.

[Dimigergo]

Oh, thanks, it works in this way, so it is a good solution for me. :)

[batzen]

This issue will be fixed if #2992 is merged.