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 the way to attach an event handler using Lambda expression.

For example:

button.Click += new EventHandler(delegate (Object s, EventArgs e) {
            //some code
        });

Can be rewritten using lambda as follows:

button.Click += (s,e) => {
            //some code
        };

One thing to note here. It is not necessary to write 's' and 'e'. You can use any two letters, e.g.

button.Click += (o,r) => {};

The first parameter would represent the object that fired the event and the second would hold data that can be used in the eventhandler.

Answer 2

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) {

}

Answer 3

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.

Answer 4

It is a shorthand for an event handler. s --> object sender and e --> some type of EventArgs.

It can also be rewrriten as:

public void HandlerFunction(object sender, EventArgs e)
{
   this.loaded = true;
}