Enable Direct Color Changes Using Theme Resources in C# for WinUI3

[Zakariathr22]

Proposal: Enable Direct Color Changes Using Theme Resources in C# for WinUI3

Summary

I propose a feature for WinUI3 that enables direct color changes using theme resources in C#. This would allow colors to dynamically adapt when the theme changes, improving the application’s aesthetics and user experience.

Rationale

• Consistency: Allowing direct color changes using theme resources in C# would align with the existing capability in XAML, providing a consistent developer experience across both languages.
• Dynamic UI: This feature would enable the UI to dynamically adapt to theme changes, enhancing the visual appeal of applications and improving the user experience.
• Ease of Development: Developers would have more flexibility and control over the UI design directly from the C# code, potentially simplifying the development process.
• Accessibility: With dynamic color changes, applications could better support accessibility features like high contrast themes, benefiting users with visual impairments.
• Future-Proofing: As theme customization becomes more prevalent in modern applications, this feature would ensure that WinUI applications remain relevant and adaptable to user preferences.

Scope

Capability	Priority
The feature must allow developers to directly change colors using theme resources in C# for WinUI3	Must
The feature should enhance the user experience by dynamically adapting UI colors to theme changes	Should
The feature could simplify the development process by providing more control over UI design from C# code	Could
The feature won’t change the existing functionality of static resources in XAML and C#	Won’t

Important Notes

Currently, we have the ability to change colors using static resources in both XAML and C# code. For instance:

• XAML Code:

  <TextBox x:Name="fullNameTextBox" PlaceholderText="FullName" Background="{StaticResource SystemFillColorCriticalBackgroundBrush}"/>

• C# Code:

  fullNameTextBox.Background = App.Current.Resources["SystemFillColorCriticalBackgroundBrush"] as Brush;

  This works well, but when it comes to using theme resources, we can only change colors in XAML. For example:

  <TextBox x:Name="fullNameTextBox" PlaceholderText="FullName" Background="{ThemeResource SystemFillColorCriticalBackgroundBrush}"/>

  Unfortunately, directly changing colors using theme resources in C# for WinUI3 is not currently supported. This limitation becomes apparent when the app’s theme changes after launch. Using the Previous C# code, colors remain static and do not update to reflect the new theme.

Therefore, it would be highly beneficial to have a feature that allows direct color changes using theme resources in C# for WinUI3. This would ensure that the colors adapt dynamically when the theme changes, enhancing the user experience and the overall aesthetic of the application.

Open Questions

Is there a workaround that can be used to achieve this until the feature is rolled out?

[Zakariathr22]

Workaround

XAML

Define a Style in the Resources section that applies theme-based brushes.

<Page
    x:Class="YourNamespace.YourPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

    <Page.Resources>
        <!-- Define a Style that applies theme-based background -->
        <Style x:Key="CriticalTextBoxStyle" TargetType="TextBox">
            <Setter Property="Background" Value="{ThemeResource SystemFillColorCriticalBackgroundBrush}" />
            <Setter Property="Foreground" Value="{ThemeResource SystemFillColorCriticalTextBrush}" />
        </Style>
    </Page.Resources>

    <Grid>
        <TextBox x:Name="myTextBox" PlaceholderText="Enter text here"/>
    </Grid>
</Page>

C

In the code-behind, access these resources and apply them to your controls:

public sealed partial class YourPage : Page
{
    public YourPage()
    {
        this.InitializeComponent();

        // Apply the style defined in XAML to the TextBox
        myTextBox.Style = (Style)this.Resources["CriticalTextBoxStyle"];
    }
}

Explanation

We still can't implement theme resource in C# without going through XAML, it would be easier if there was a way to use it directly from C# code.

This workaround provides a flexible and lightweight method to achieve dynamic theme-based coloring directly in C# until the feature for direct theme resource application in C# is implemented in WinUI3.