How to detect light or dark colour mode

[SimonORorke]

How can a desktop application that uses a light/dark colour mode-sensitive Fluent theme find out the operating system's colour mode?

Usage example. I want to colour-code the text in each data row of a DataGrid depending on the value of a property of the row's corresponding view model. Given that the row background colour will be determined by the colour mode , some colour variants look good in dark mode but not light mode and vice versa.

private static void DataGridOnLoadingRow(object? sender, DataGridRowEventArgs e) {
    // How to detect the operating system's colour mode?
    // These colours look good in Dark colour mode. 
    var controlViewModel = (ControlViewModel)e.Row.DataContext!;
    e.Row.Foreground = controlViewModel.ColourId switch {
        1 => Brushes.Chartreuse,
        2 => Brushes.DarkOrange,
        3 => Brushes.Red,
        4 => Brushes.Yellow,
        _ => Brushes.White
    };
// These colours look good in Light colour mode. 
// e.Row.Foreground = controlViewModel.ColourId switch {
//     1 => Brushes.ForestGreen,
//     2 => Brushes.DarkOrange,
//     3 => Brushes.Red,
//     4 => Brushes.DarkGoldenrod,
//     _ => Brushes.Black
// };
}

[thevortexcloud]

I believe you can use one of these:

Avalonia/src/Avalonia.Controls/Application.cs

Lines 93 to 102 in 230e4fd

	public ThemeVariant? RequestedThemeVariant
	{
	get => GetValue(RequestedThemeVariantProperty);
	set => SetValue(RequestedThemeVariantProperty, value);
	}
	/// <inheritdoc />
	[System.Diagnostics.CodeAnalysis.SuppressMessage("AvaloniaProperty", "AVP1031", Justification = "This property is supposed to be a styled readonly property.")]
	[System.Diagnostics.CodeAnalysis.SuppressMessage("AvaloniaProperty", "AVP1030", Justification = "False positive.")]
	public ThemeVariant ActualThemeVariant => GetValue(ActualThemeVariantProperty);

But I have not tried it.

[SimonORorke]

Basically repeating a comment I somehow accidentally deleted.
Thanks, @thevortexcloud ! That works. I'd mark your comment as the answer. But I now realise I should have posted in the Q&A section to do that.

private void DataGridOnLoadingRow(object? sender, DataGridRowEventArgs e) {
    if (ActualThemeVariant == ThemeVariant.Dark) {
        // These colours look good in Dark colour mode
        e.Row.Foreground = controlViewModel.ColourId switch {
            ColourId.Green => Brushes.Chartreuse,
            ColourId.Orange => Brushes.DarkOrange,
            ColourId.Red => Brushes.Red,
            ColourId.Yellow => Brushes.Yellow,
            _ => Brushes.White
       };
    } else { // ThemeVariant.Light
        // These colours look good in Light colour mode
        e.Row.Foreground = controlViewModel.ColourId switch {
            ColourId.Green => Brushes.ForestGreen,
            ColourId.Orange => Brushes.DarkOrange,
            ColourId.Red => Brushes.Red,
            ColourId.Yellow => Brushes.DarkGoldenrod,
            _ => Brushes.Black
        };
    }
}

[thevortexcloud]

All good. Glad I could help.