如何取消注册"匿名"事件处理程序

Question

说如果我听一个事件:

Subject.NewEvent += delegate(object sender, NewEventArgs e)
{
    //some code
}); 

现在我如何取消注册此活动？或者只是让内存泄漏？

Answer 1

为匿名委托的实例命名:

EventHandler<NewEventArg> handler = delegate(object sender, NewEventArgs e)
{
    //some code
};

Subject.NewEvent += handler;
Subject.NewEvent -= handler;

Answer 2

如果您需要取消注册事件,我建议您避免使用事件处理程序的匿名委托.

这是一种情况,将此分配给本地方法更好 - 您可以干净地取消订阅事件.

Answer 3

要在第一次调用时删除处理程序:

//SubjectType Subject = ..... already defined if using (2)

EventHandler handler = null;
handler = delegate(object sender, EventArgs e)
{
    // (1)
    (sender as SubjectType).NewEvent -= handler;
    // or
    // (2) Subject.NewEvent -= handler;

    // do stuff here
};

Subject.NewEvent += handler;

Answer 4

您可以创建从所有事件侦听器取消注册的方法.这不完全是你想要的,但有时它可能是有帮助的.例如(这确实有效=)):

    class Program {
    static void Main(string[] args) {
        A someClass = new A();
        someClass.SomeEvent += delegate(object sender, EventArgs e) {
            throw new NotImplementedException();
        };

        someClass.ClearEventHandlers();
        someClass.FireEvent();

        Console.WriteLine("No error.");
    }

    public class A {
        public event EventHandler SomeEvent;

        public void ClearEventHandlers() {
            Delegate[] delegates = SomeEvent.GetInvocationList();
            foreach (Delegate delegate in delegates) {
                SomeEvent -= (EventHandler) delegate;
            }
        }

        public void FireEvent() {
            if (SomeEvent != null) {
                SomeEvent(null, null);
            }
        }
    }
}