如何实现可取消事件？ [英] How do I implement a cancelable event?

问题描述

在System.ComponentModel中，有一个名为CancelEventArgs的类，其中包含可以在事件侦听器中设置的Cancel成员。 MSDN上的文档解释了如何使用它来从监听器中取消事件，但是如何使用它来实现我自己的可取消事件？有没有办法在每个监听器触发之后检查取消成员，或者我必须等待事件触发所有监听器之后？

In System.ComponentModel, there's a class called CancelEventArgs which contains a Cancel member that can be set in event listeners. The documentation on MSDN explains how to use that to cancel events from within a listener, but how do I use it to implement my own cancelable events? Is there a way to check the Cancel member after each listener fires, or do I have to wait until after the event has fired all its listeners?

推荐答案

要依次查看每个监听器，您需要通过GetInvocationList手动获取处理程序：

To check each listener in turn, you need to manually get the handlers via GetInvocationList:

class Foo
{
    public event CancelEventHandler Bar;

    protected void OnBar()
    {
        bool cancel = false;
        CancelEventHandler handler = Bar;
        if (handler != null)
        {
            CancelEventArgs args = new CancelEventArgs(cancel);
            foreach (CancelEventHandler tmp in handler.GetInvocationList())
            {
                tmp(this, args);
                if (args.Cancel)
                {
                    cancel = true;
                    break;
                }
            }
        }
        if(!cancel) { /* ... */ }
    }
}

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