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 is an assignment of a delegate instance (the start of a lambda expression) to an event invocation list. The s, e represents the sender and EventArgs parameters of the event delegate type.

See http://msdn.microsoft.com/en-us/library/ms366768.aspx for more info.