Event Procedures

Code in a Visual Basic application is divided into smaller blocks called procedures. An event procedure contains code that is executed when an event occurs (such as when a user clicks a button or types something in the text box). In chapter 4 (The Classic hello World Program), you saw what happened when you clicked the "Show" button. Most events come directly from the user at the keyboard and mouse running applications within Windows.

When Windows recognizes that a user triggered an event and the event is not a system event, it passes that event to the application.

If you have written an event procedure to respond to that particular event, your application will respond to that event. To the contrary, if you haven't written an event procedure, the event goes unhandled.

An event procedure for a control combines the control's actual name (specified in the Name property), an underscore (_), and the event name. For example, if you want a command button named "Show" to invoke an event procedure when it is clicked, use the procedure Show_Click.

Visual Basic supports two kinds of procedures: functions and subroutines. All event procedures will be subroutines. A subroutine is indicated by the sub keyword, and it does not return a value. On the contrary, a function can return a value to somewhere else in the program. The keyword Function indicates that a procedure is a function.