Get ThemeResource textbox / richeditbox foreground and background color properties from code behind

[iomismo]

Making a basic text editor with WinUI, MVVM. Stucked in default RichEditBox foreground and background color viewmodel properties based on selected theme, to show them in AppBar ColorPickerButtons (from CommunityToolkit, same results with "basic" ColorPicker).

Using Application.Current.Resources[]:

Tried different resource names and still not getting correct colors in dark theme (white foreground and whatever background color uses RichEditBox). They always show light theme colors:

• TextControlForegroundFocused (that TextBox Class msdn page states it is "Text color when focused")
• TextFillColorPrimary
• SystemControlBackgroundAltHighBrush
• SystemColorButtonFaceColor
• SystemColorButtonTextColor

Same results using new TextBox().Resources as property value (TextBox because, again, msdn TextBox class page states that resources used by TextBox are shared with RichEditBox, among other controls. Same results using RichEditBox):

• TextBoxForegroundThemeBrush
• TextBoxBackgroundThemeBrush

So maybe the question is how to know what specific resource / themeresource names are used in specific control properties. I see resource names in resource xaml files are very descriptive but for now it is a mess for me. Also, I never see dark theme in those files, only Default, Light and HighContrast, and there are no colors matching dark theme, so it is evident that I am missing something (or many things :)

Actually, using in xaml works with selected theme, e.g:
<controls:ColorPickerButton SelectedColor="{ThemeResource SystemBaseHighColor}"/>

But not if using it in code:

<!--xaml-->
<controls:ColorPickerButton SelectedColor="{x:Bind ViewModel.SelectedForeColor, Mode=TwoWay}"/>

// cs
private Color _selectedForeColor = Application.Current.Resources["SystemBaseHighColor"];

It always shows white foreground color, despite of selected theme.

[jschwizer99]

Seems to be related to #3783 (comment).

Meanwhile, I use the following code

// It shows one of the work-arounds for the missing DynamicResource issue.
// The problem is that winrt::Microsoft::UI::Xaml::Application::Current().Resources() itself does not update dynamically
// its theme resources. Thus, we need to search through the MergedDictionaries() to find the proper theme resource.
// This is an awful workaround just to get a proper resource value.
winrt::Microsoft::UI::Xaml::Media::Brush getThemeBrush(winrt::Microsoft::UI::Xaml::ElementTheme const& theme, winrt::hstring const& style)
{
	std::wstring themeString = (theme == Microsoft::UI::Xaml::ElementTheme::Dark) ? L"Dark" : L"Light";
	winrt::Windows::Foundation::IInspectable themeResource = nullptr;
	for (const auto& mergedDirectory : winrt::Microsoft::UI::Xaml::Application::Current().Resources().MergedDictionaries())
	{
		// Its hard to find a stable solution to identify the correct merged
		// directory as we cannot use HasKey(). Currently, we assume that we
		// have only "Light" and "Dark" custom themes. The first directory
		// has 3 themes.
		// See https://docs.microsoft.com/en-us/uwp/api/windows.ui.xaml.resourcedictionary?view=winrt-19041
		if (mergedDirectory.ThemeDictionaries().Size() == 2)
		{
			themeResource = mergedDirectory.ThemeDictionaries().TryLookup(winrt::box_value(themeString));
			break;
		}
	}
	if (themeResource)
	{
		winrt::Windows::Foundation::IInspectable color = themeResource.as<winrt::Microsoft::UI::Xaml::ResourceDictionary>().TryLookup(winrt::box_value(style));
		if (color)
		{
			auto c = winrt::unbox_value<winrt::Microsoft::UI::Xaml::Media::SolidColorBrush>(color).Color();
			return winrt::Microsoft::UI::Xaml::Media::Brush(
				winrt::unbox_value<winrt::Microsoft::UI::Xaml::Media::SolidColorBrush>(color));
		}
	}
	return nullptr;
}