How do I implement a cancelable event?
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n 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?
To check each listener in turn, you need to manually get the handlers via GetInvocationList:
http://stackoverflow.com/questions/295254/how-do-i-implement-a-cancelable-event
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) { /* ... */ }
}
}
http://stackoverflow.com/questions/295254/how-do-i-implement-a-cancelable-event