what is the meaning of “ += ( s, e )” in the code?

Question

What is exactly the += ( s, e ) in the code?

example:

this.currentOperation.Completed += ( s, e ) => this.CurrentOperationChanged();

Answer 1

This codes adds an event listener in form of a Lambda expression. s stands for sender and e are the EventArgs. Lambda for

private void Listener(object s, EventArgs e) {

}