Adding and Removing Anonymous Event Handler

c# events anonymous-methods
HaxElit picture HaxElit · Jan 12, 2010 · Viewed 44.5k times · Source

I was wondering if this actually worked ?

private void RegisterKeyChanged(T item) 
{
    item.OnKeyChanged += (o, k) => ChangeItemKey((T)o, k);
}

private void UnRegisterKeyChanged(T item) 
{
    item.OnKeyChanged -= (o, k) => ChangeItemKey((T)o, k);
}

How does the compiler know that the event handlers are the same ? Is this even recommended?

Answer

Ryan Lundy picture Ryan Lundy · Jan 12, 2010

There's an MSDN page that talks about this:

How to Subscribe to and Unsubscribe from Events

Note in particular:

If you will not have to unsubscribe to [sic] an event later, you can use the addition assignment operator (+=) to attach an anonymous method to the event.

And also:

It is important to notice that you cannot easily unsubscribe from an event if you used an anonymous function to subscribe to it. To unsubscribe in this scenario, it is necessary to go back to the code where you subscribe to the event, store the anonymous method in a delegate variable, and then add the delegate to the event . In general, we recommend that you do not use anonymous functions to subscribe to events if you will have to unsubscribe from the event at some later point in your code.

Related questions

How do I Unregister 'anonymous' event handler

Say if I listen for an event: Subject.NewEvent += delegate(object sender, NewEventArgs e) { //some code }); Now how do I un-register this event? Or just allow the memory to leak?

Read More
How to remove all event handlers from an event

To create a new event handler on a control you can do this c.Click += new EventHandler(mainFormButton_Click); or this c.Click += mainFormButton_Click; and to remove an event handler you can do this c.Click -= mainFormButton_Click; …

Read More
Understanding events and event handlers in C#

I understand the purpose of events, especially within the context of creating user interfaces. I think this is the prototype for creating an event: public void EventName(object sender, EventArgs e); What do event handlers do, why are they needed, …

Read More