Visual Basic 2012 Programmer's Reference

ADDING CODE TO CONTROLS

After you have added controls to a form and set their properties, the next step is to add code to the form that responds to control events and that manipulates the controls.

You use the code editor to write code that responds to control events. The code editor is described in Chapter 5, “Visual Basic Code Editor,” but you can open the code editor from the Windows Forms Designer.

An event handler is a code routine that catches an event raised by a control and takes some action. Almost all program action is started from an event handler. Even actions started automatically by a timer or when a form first appears begin when an event handler catches a timer’s events.

If you double-click a control on the Windows Forms Designer, Visual Studio creates an empty event handler to handle the control’s default event and it opens the event handler in the code editor. For example, the following code shows the event handler the IDE built for a Button control named Button1. The default event for a Button is Click, so this code is a Click event handler.

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
 
End Sub

RELAX, DON’T WORRY

Relaxed delegates let you remove the parameters from the event handler’s declaration if you don’t need them. For example, if you use separate event handlers for each button, you probably don’t need the parameters to figure out what’s happening. If the user clicks the button named btnExit, the btnExit_Click event ...