dotnet/CommunityToolkit.Common/Collections/IReadOnlyObservableGroup.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System.ComponentModel;

namespace CommunityToolkit.Common.Collections;

/// <summary>
/// An interface for a grouped collection of items.
/// It allows us to use x:Bind with <see cref="ObservableGroup{TKey, TValue}"/> and <see cref="ReadOnlyObservableGroup{TKey, TValue}"/> by providing
/// a non-generic type that we can declare using x:DataType.
/// </summary>
public interface IReadOnlyObservableGroup : INotifyPropertyChanged
{
    /// <summary>
    /// Gets the key for the current collection, as an <see cref="object"/>.
    /// It is immutable.
    /// </summary>
    object Key { get; }

    /// <summary>
    /// Gets the number of items currently in the grouped collection.
    /// </summary>
    int Count { get; }
}