namespace ConsoleApplication1
{
    public class Program
    {
        public static void Main(string[] args)
        {
            Program A = new Program();
 
            //本来メソッドスコープないの変数はメソッド中に
            //回収される事はありませんが、
            //WeakReferenceで囲う事でGCで回収可能にします。
            var oldR = new WeakReference(new ReceiverOld(A));
            var newR = new WeakReference(new ReceiverNew(A));
 
            A.RaiseTestEvent();//１回目のイベント呼び出し
 
            //ガベージコレクションの実行
            GC.Collect();
            GC.WaitForPendingFinalizers();
            GC.Collect();
 
            A.RaiseTestEvent();//2回目のイベント呼び出し
 
            //--結果 -- 
            //
            // ReceiverOld Received ! 
            // ReceiverNew Received ! 
            // ReceiverOld Received ! 
            //
            //２度目のイベント呼び出しではReceiverNewのイベントハンドラが呼び出されていない！
            //
            //GC後もProgram AがRecieveOldのイベントハンドラを参照しているから、
            //oldAオブジェクトはGCに回収されていません。
            //
            //しかし今回の汎用WeakEventListenerを使ったnewAオブジェクトは見事回収されています。
 
            Console.ReadLine();
        }
 
        private void RaiseTestEvent()
        {
            var handler = TestEvent;
            if (handler != null)
            {
                handler(this, new RoutedEventArgs());
            }
        }
 
        public event RoutedEventHandler TestEvent;
    }
 
    //通常通りイベントを受信しているオブジェクト
    public class ReceiverOld
    {
        public ReceiverOld(Program b)
        {
            b.TestEvent += OnTestEvent;
        }
 
        void OnTestEvent(object sender, RoutedEventArgs e)
        {
            Console.WriteLine("ReceiverOld Received ! ");
        }
    }
 
    //今回の汎用WeakEventListener使ってイベントを受信しているオブジェクト
    public class ReceiverNew
    {
        LivetWeakEventListener<RoutedEventHandler, RoutedEventArgs> _listener;//リスナへの強い参照を保持
 
        public ReceiverNew(Program b)
        {
            _listener = new LivetWeakEventListener<RoutedEventHandler, RoutedEventArgs>(
                h => new RoutedEventHandler(h),//このhはEventHandler<RoutedEventArgs>
                h => b.TestEvent += h,//このhはRoutedEventHandler
                h => b.TestEvent -= h,//このhはRoutedEventHandler
                OnTestEvent);//本来のハンドラ
        }
 
        void OnTestEvent(object sender, System.Windows.RoutedEventArgs e)
        {
            Console.WriteLine("ReceiverNew Received ! ");
        }
 
 
    }
}

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