Avalonia/src/Avalonia.Native/NativePlatformSettings.cs

using System;
using Avalonia.Media;
using Avalonia.Native.Interop;
using Avalonia.Platform;

namespace Avalonia.Native;

internal class NativePlatformSettings : DefaultPlatformSettings
{
    private readonly IAvnPlatformSettings _platformSettings;
    private PlatformColorValues _lastColorValues;

    public NativePlatformSettings(IAvnPlatformSettings platformSettings)
    {
        _platformSettings = platformSettings;
        platformSettings.RegisterColorsChange(new ColorsChangeCallback(this));
    }

    public override PlatformColorValues GetColorValues()
    {
        var (theme, contrast) = _platformSettings.PlatformTheme switch
        {
            AvnPlatformThemeVariant.Dark => (PlatformThemeVariant.Dark, ColorContrastPreference.NoPreference),
            AvnPlatformThemeVariant.Light => (PlatformThemeVariant.Light, ColorContrastPreference.NoPreference),
            AvnPlatformThemeVariant.HighContrastDark => (PlatformThemeVariant.Dark, ColorContrastPreference.High),
            AvnPlatformThemeVariant.HighContrastLight => (PlatformThemeVariant.Dark, ColorContrastPreference.High),
            _ => throw new ArgumentOutOfRangeException()
        };
        var color = _platformSettings.AccentColor;

        if (color > 0)
        {
            _lastColorValues = new PlatformColorValues
            {
                ThemeVariant = theme,
                ContrastPreference = contrast,
                AccentColor1 = Color.FromUInt32(color)
            };
        }
        else
        {
            _lastColorValues = new PlatformColorValues
            {
                ThemeVariant = theme,
                ContrastPreference = contrast
            };
        }

        return _lastColorValues;
    }

    public void OnColorValuesChanged()
    {
        var oldColorValues = _lastColorValues;
        var colorValues = GetColorValues();

        if (oldColorValues != colorValues)
        {
            OnColorValuesChanged(colorValues);
        }
    }

    private class ColorsChangeCallback : NativeCallbackBase, IAvnActionCallback
    {
        private readonly NativePlatformSettings _settings;

        public ColorsChangeCallback(NativePlatformSettings settings)
        {
            _settings = settings;
        }
        
        public void Run()
        {
            _settings.OnColorValuesChanged();
        }
    }
}