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我正在附加到第 3 方，长期存在的 Deleted 事件发布者，由于事件处理程序，它最终使我可能短暂存在的对象保持活动状态。Deleted 事件很可能永远不会触发，如果是，我只需要处理。取消订阅 Deleted 事件的位置并不明显，因此我希望对它进行弱引用，以便我的对象可以被 GC 处理。

我已经看到了很多非常精细的方法来创建弱事件处理程序，但是下面的代码片段似乎可以解决问题，至少在提供的测试代码片段中是这样。这只是疯了还是可以工作？

（http://diditwith.net/CommentView,guid,aacdb8ae-7baa-4423-a953-c18c1c7940ab.aspx在“A First Stab”下说类似的片段“（...）不够健壮，无法与一个事件（...）”，为什么不呢？）

public static class WeakEvent
{
    private class WeakEventHolder<TArgs> where TArgs : EventArgs
    {
        private readonly WeakReference _handler;

        public WeakEventHolder(Action<object, TArgs> handler)
        {
            _handler = new WeakReference(handler);
        }

        public void Handle(object sender, TArgs args)
        {
            Action<object, TArgs> handler = (Action<object, TArgs>)_handler.Target;
            if (handler != null)
                handler(sender, args);
        }
    }

    public static EventHandler MakeHandler(Action<object, EventArgs> handler)
    {
        return new WeakEventHolder<EventArgs>(handler).Handle;
    }
}

测试班

[TestFixture]
public class Tests
{
    public class Publisher
    {
        public EventHandler Event;

        public void Raise()
        {
            if (Event != null)
                Event(this, EventArgs.Empty);
        }
    }

    public class Target
    {
        public Target(Publisher publisher)
        {
            publisher.Event += WeakEvent.MakeHandler(HandleEvent);
        }

        public void HandleEvent(object sender, EventArgs args)
        {
            System.Diagnostics.Trace.WriteLine("HandleEvent");
        }
    }

    [Test]
    public void Test()
    {
        Publisher publisher = new Publisher();
        WeakReference wref = new WeakReference(new Target(publisher));
        GC.Collect();

        publisher.Raise();

        Assert.False(wref.IsAlive);
    }
}
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1 回答 1

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Because Action<object, TArgs> handler maybe garbage collected before it's target is. Here's a unit test that exposes the problem:

public class Bar
{
    public void Foo(object sender, EventArgs args)
    {
    }
}

[Test]
public void ActionIsNotGCedBeforeTarget()
{
    Bar bar = new Bar();
    Action<object, EventArgs> action = bar.Foo;
    WeakReference weakRef = new WeakReference(action);
    action = null;
    GC.Collect();

    Assert.IsTrue(weakRef.IsAlive); // Will be false
}
于 2013-10-09T07:53:35.070 回答