James,

   Typically the pattern for an event handler is to have two parameters.
The first, sender, is the object that fired the event.

   The second is to have a class that derives from EventArgs which has any
additional information about the event which might not be immediately
available to the caller.

   For example, a MouseMove event has information on the MouseEventArgs
instance passed to the event handler which indicates the position of the
mouse at the time the event was fired.  This information isn't part of the
regular information that the Control class exposes, so it is exposed through
the MouseEventArgs.