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Weak Events in C#

, 25 Apr 2009
Different approaches to weak events
// Copyright (c) 2008 Daniel Grunwald
// 
// Permission is hereby granted, free of charge, to any person
// obtaining a copy of this software and associated documentation
// files (the "Software"), to deal in the Software without
// restriction, including without limitation the rights to use,
// copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following
// conditions:
// 
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
// OTHER DEALINGS IN THE SOFTWARE.

using System;

/* Requires a reference to WPF.
namespace WeakEvents
{
	/// <summary>
	/// WeakEventManager with AddListener/RemoveListener and CurrentManager implementation.
	/// Helps implementing the WeakEventManager pattern with less code.
	/// </summary>
	public abstract class WeakEventManagerBase<TManager, TEventSource> : WeakEventManager
		where TManager : WeakEventManagerBase<TManager, TEventSource>, new()
		where TEventSource : class
	{
		/// <summary>
		/// Creates a new WeakEventManagerBase instance.
		/// </summary>
		protected WeakEventManagerBase()
		{
			Debug.Assert(GetType() == typeof(TManager));
		}
		
		/// <summary>
		/// Adds a weak event listener.
		/// </summary>
		[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1000:DoNotDeclareStaticMembersOnGenericTypes")]
		public static void AddListener(TEventSource source, IWeakEventListener listener)
		{
			CurrentManager.ProtectedAddListener(source, listener);
		}
		
		/// <summary>
		/// Removes a weak event listener.
		/// </summary>
		[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1000:DoNotDeclareStaticMembersOnGenericTypes")]
		public static void RemoveListener(TEventSource source, IWeakEventListener listener)
		{
			CurrentManager.ProtectedRemoveListener(source, listener);
		}
		
		/// <inheritdoc/>
		protected sealed override void StartListening(object source)
		{
			StartListening((TEventSource)source);
		}
		
		/// <inheritdoc/>
		protected sealed override void StopListening(object source)
		{
			StopListening((TEventSource)source);
		}
		
		/// <summary>
		/// Attaches the event handler.
		/// </summary>
		protected abstract void StartListening(TEventSource source);
		
		/// <summary>
		/// Detaches the event handler.
		/// </summary>
		protected abstract void StopListening(TEventSource source);
		
		/// <summary>
		/// Gets the current manager.
		/// </summary>
		[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1721:PropertyNamesShouldNotMatchGetMethods")]
		protected static TManager CurrentManager {
			get {
				Type managerType = typeof(TManager);
				TManager manager = (TManager)GetCurrentManager(managerType);
				if (manager == null) {
					manager = new TManager();
					SetCurrentManager(managerType, manager);
				}
				return manager;
			}
		}
	}
}
*/

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License

This article, along with any associated source code and files, is licensed under The MIT License

About the Author

Daniel Grunwald

Germany Germany
I am the lead developer on the SharpDevelop open source project.
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