C# - anonymous functions and event handlers

Question

I have the following code:

public List FindStepsByType(IWFResource res)  
{  
    List retval = new List&         


        

Answer 1

When using an anonymous delegate (or a lambda expression) to subscribe to an event does not allow you to easily unsubscribe from that event later. An event handler is never automatically unsubscribed.

If you look at your code, even though you declare and subscribe to the event in a function, the event you are subscribing to is on the class, so once subscribed it will always be subscribed even after the function exits. The other important thing to realize is that each time this function is called, it will subscribe to the event again. This is perfectly legal since events are essentially multicast delegates and allow multiple subscribers. (This may or may not be what you intend.)

In order to unsubscribe from the delegate before you exit the function, you would need to store the anonymous delegate in a delegate variable and add the delegate to the event. You should then be able to remove the delegate from the event before the function exits.

For these reasons, if you will have to unsubscribe from the event at some later point it is not recommended to use anonymous delegates. See How to: Subscribe to and Unsubscribe from Events (C# Programming Guide) (specifically the section titled "To subscribe to events by using an anonymous method").