C# unhook event

Question

I am using standard windows forms controls under C#.

Short version: is there any problem unhooking a delegate which hasn't been hooked?

Full question:

I have two controls which are different ways of setting a single value. Thus when one is changed, the changed event handler computes a value for the other and sets it. So I need to unhook the change event on the second control temporarily to prevent looping (A changes B, B is changed so it changes A, A is changed...). There are also some other situations where I need to stop the change event. So there are several places where I need to unhook the event, and only one place where it needs to be hooked.

My question is: do I need to keep track of whether the event has been hooked or can I just unhook it as many times as I like and only occasionally hook it again? (Is there any documentation that addresses this?)

Answer 1

Ya, you can unhook it as many times as you want, no exceptions will be thrown.

Answer 2

Unhooking an event handler that was never registered using the -= operator won't give you any problems.

Answer 3

This will loop through and unhook any subscribed methods:

Delegate[] subscribers = myEvent.GetInvocationList();

    for(int i = 0; i < subscribers.Length; i++)

    {

    myEvent -= subscribers[i] as yourDelegateType;

    }

However, I think you should be able to avoid the looping problem by writing a single handler with logic to determine how the data should be modified. This would be cleaner and more maintainable.