Avalonia/src/Avalonia.Base/Controls/IThemeVariantProvider.cs

using Avalonia.Metadata;
using Avalonia.Styling;

namespace Avalonia.Controls;

/// <summary>
/// Resource provider with theme variant awareness.
/// Can be used with <see cref="IResourceDictionary.ThemeDictionaries"/>.
/// </summary>
/// <remarks>
/// This is a helper interface for the XAML compiler to make Key property accessibly by the markup extensions.
/// Which means, it can only be used with ResourceDictionaries and markup extensions in the XAML code.
/// This API might be removed in the future minor updates.
/// </remarks>
[Unstable]
public interface IThemeVariantProvider : IResourceProvider
{
    /// <summary>
    /// Key property set by the compiler.
    /// </summary>
    ThemeVariant? Key { get; set; }
}