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Proposal: Non-XAML ThemeResource #10029

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Proposal: Non-XAML ThemeResource#10029

Description

@MartinZikmund

MartinZikmund
openedon Oct 1, 2024

Proposal: Non-XAML ThemeResource

Summary

Currently it is only possible to set ThemeResource from XAML, which is problematic in various scenarios, for example in Uno Platform's C# Markup:

This is especially problemtai

Rationale

  • It is not possible to retrieve a theme-dependent brush for a given theme from a ResourceDictionary in code
  • It is not possible to set a property like Background or BorderBrush of a control to a theme-dependent brush in code

Scope

Capability Priority
Retrieve a theme-dependent value of a resource from ResourceDictionary in code Must
Set a control's dependency property to a theme-dependent resource in code Must

Workarounds

There some very limited ways to work around this, like:

microsoft-ui-xaml/src/controls/dev/WebView2/WebView2.cpp

Lines 909 to 927 in 66a7b0a

winrt::Color WebView2::GetThemeBackgroundColor()
{
bool isHighContrast = GetAccessibilitySettings().HighContrast();
std::wstring helperBrushName = isHighContrast ? L"BrushForThemeBackgroundColor_HC" : L"BrushForThemeBackgroundColor";
// Ensure helper SCB referencing appropriate color as a ThemeResource is added to WV2.Resources.
// This is needed since programatic lookup of theme resources themselves does not account for active theme.
if (!this->Resources().HasKey(box_value(helperBrushName)))
{
std::wstring resourceName = isHighContrast ? L"SystemColorWindowColor" : L"SolidBackgroundFillColorBase";
winrt::SolidColorBrush helperBrush = winrt::XamlReader::Load(
L"<SolidColorBrush xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation' "
L"xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml' "
L"x:Name='" + helperBrushName + L"' "
L"Color='{ThemeResource " + resourceName + L"}'/>"
).as<winrt::SolidColorBrush>();
this->Resources().Insert(box_value(helperBrushName), helperBrush);
}
, but these are very inefficient and definitely not ideal.

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