c# - Why do event handlers always have a return type of void?

Question

Hey, I wondered why is it that the return type of events such as

private void button1_Click(object sender, EventArgs e)

is always void?

Can it return any other value too?

Answer 1

An event handler signature, that is the return type and the number and types of arguments it takes, are determined by the signature of the delegate used to define the event. So the Click event of the Button in your example does not support any return values.

Typically you would not expect to return a value from an event handler as a function return value because an event can have multiple subscribers and each would be returning a return value independently of the other handlers and would require special event firing code to decide what to do with all the return values.

Typically, if you need to communicate back from an event handler the EventArgs structure would contain members that the handler can update and each handler will get an opportunity to look at the values and update accordingly, and the code firing the event only needs to react to the final value in the structure.