By convention, .NET events have two parameters that specify the event sender and event data. Event handler signatures should ...

By convention, .NET events have two parameters that specify the event sender and event data. Event handler signatures should follow this form: void MyEventHandler(object sender, EventArgs e). The 'sender' parameter is always of type System.Object, even if it is possible to employ a more specific type. The 'e' parameter is always of type System.EventArgs. Events that do not provide event data should use the System.EventHandler delegate type. Event handlers return void so that they can send each event to multiple target methods. Any value returned by a target would be lost after the first call.