What's a proper way to unsibscribe from events in c#?

Question

I have a model class with an event which I subscribe from other classes. I want to subscribe and un-subscribe in each class correctly.

• First I want to guarant

Answer 1

You can also control subscriptions and unsubsriptions with this declaration. But you also have to iterate through dictionary and call manually subscribed delegates.

    private Dictionary<string, EventHandler> TestEvents { get; }

    public event EventHandler TestEvent
    {
        add
        {
            string name = value.GetType().FullName;
            if (!TestEvents.ContainsKey(name))
            {
                TestEvents.Add(name, value);
            }
        }
        remove
        {
            string name = value.GetType().FullName;
            if (TestEvents.ContainsKey(name))
            {
                TestEvents.Remove(name);
            }
        }
    }

Answer 2

You can safely unsubscribe the same handler from an event multiple times. Additional checking is not required and would be contraproductive.

Answer 3

If you only subscribe once, it doesn't matter how many times you unsubscribe - unsubscribing when you don't have a subscription is a no-op. Equally, the entire point of the event API is that you can't accidentally unsubscribe other subscriptions (either other types, or other instances of the same type).

As such, the code as shown should be fine, although it might be worth moving the two calls to a single method that handles this. That might be overkill, though.

Also, if your type is IDisposable, make sure it gets called in that code-path too (presumably by calling Close()).

Answer 4

If you want to guarantee you only unsubscribe once, you can use the GetInvocationList method:

if (_model.OnMyEvent != null && _model.GetInvocationList().Contains(EventHandle))
{
    _model.OnMyEvent -= EventHandle
}

But as mentioned by the others, you can unsubscribe multiple times. If this really isn't a problem, keep it that way. The solution I propose is just code-noise. Simply unsubscribing in one line is much neater, and easier to read when your class starts to grow.