问题描述

我编写了一些代码来处理事件，如下所示:

I've written some code to handle an event as follows:

AddHandler myObject.myEvent, AddressOf myFunction

一开始似乎一切正常，但是当我运行调试器时，我发现 myFunction 经常会在每次 myObject.myEvent 触发时运行几次.我发现我允许代码添加事件处理程序多次运行，导致了这种行为.

It seemed that everything was working at first, but when I ran the debugger, I discovered that oftentimes, myFunction would run several times each time myObject.myEvent fired. I figured out that I had allowed the code to add the event handler to run more than once, resulting in this behavior.

有没有办法让我做这样的事情?

Is there a way I can do something like this?

If myObject.myEvent is not handled Then
  AddHandler myObject.myEvent, AddressOf myFunction
End If

推荐答案

假设发布事件的不是你的代码，你不能.这个想法是订阅者彼此隔离 - 您无法了解其他事件订阅者，自己引发事件等.

Assuming it's not your code that's publishing the event, you can't. The idea is that subscribers are isolated from each other - you can't find out about other event subscribers, raise the event yourself etc.

如果问题是您多次添加自己的处理程序，您应该能够通过跟踪您是否添加了处理程序来自己解决这个问题.Steven 在添加之前删除处理程序的想法是一个有趣的解决方法:尝试删除处理程序是有效的，即使它没有被订阅.但是，我认为这是您的应用程序不知道它应该做什么的解决方法.这是一个非常快速的短期解决方案，但我会担心将其长期保留.

If the problem is that you're adding your own handler multiple times, you should be able to fix that yourself by keeping track of whether you have added a handler. Steven's idea of removing the handler before adding it is an interesting workaround: it's valid to attempt to remove a handler even when it isn't subscribed. However, I'd regard this as a workaround to your app not really knowing what it should be doing. It's a very quick short-term fix, but I'd be worried about leaving it in for the longer term.

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