Correct usage of Action and Events

Question

I am a bit new to c# so please overlook if you find it trivial. I saw the following "weird" code.

Can anybody shed a bit of light on it.

public event Action _action;

if (_action != null)            
{
    foreach (Action c in _action.GetInvocationList())
    {
         _action -= c;
    }
}

Specially the _action -= c; part.

Answer 1

A delegate can be a delegate to more than one function. If you have a delegate alpha that delegates to Alpha() and a delegate beta that delegates to Beta() then gamma = alpha + beta; is a delegate that calls Alpha() then Beta(). gamma - beta produces a delegate that calls Alpha(). It's a bit of a weird feature, to be perfectly frank.

The code you've posted is bizarre. It says "go through the list of functions in action, produce a whole pile of delegates that invoke fewer and fewer functions, and then finally assign a delegate that does nothing to action. Why on earth would anyone do this? Just assign null to action and be done with it.

Answer 2

public event Action _action; //an event


if (_action != null) // are there any subscribers?

{
        foreach (Action c in _action.GetInvocationList()) //get each subscriber
        {
            _action -= c; //remove its subscription to the event
        }
}

Answer 3

It's removing the handlers for the action.