In the previous chapter, you have learned that
VB2010 is an object oriented programming language. You have
understood the meanings of class, object, encapsulation inheritance
as well as polymorphism. You have also learned to write some simple
programs without much understanding some underlying foundations and
theories. In this chapter, you will learn some basic theories about
VB2010 programming but we will focus more on learning by doing, i.e.
learning by writing programs .I will keep the theories short
so that it would not be too difficult for beginners.
5.1 The event Procedure
VB2010 is an object oriented and event driven programming
language. In fact, all windows applications are event driven. Event
driven means the user will decide what to do with the program,
whether he/she wants to click the command button, or he/she wants to
enter text in a text box, or he/she might wants to close the
application and etc. An event is related to an object, it is an
incident that happens to the object due to the action of the user ,
such as a click or pressing a key on the keyboard. A class has
events as it creates instant of a class or an object. When we start
a windows application in VB2010 in previous chapters, we will see a
default form with the Form1 appears in the IDE, it is actually the
Form1 Class that inherits from the Form class
System.Windows.Forms.Form, as shown in the Form1 properties
When we click on any part of the form, we will see the code
window as shown below. The is the structure of an event procedure.
In this case, the event procedure is to load Form1 and it starts
with Private Sub and end with End Sub. This procedure includes the Form1 class and the event Load,
and they are bind together with an underscore, i.e. Form_Load. It
does nothing other than loading an empty form. You don't have to
worry the rest of the stuff at the moment, they will be explained in
Public Class Form1
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
The are other events associated with the Form1
class, such as click, cursorChanged, DoubleClick, DragDrop, Enter as
so on, as shown in the diagram below (It appears when you click on
the upper right pane of the code window)
5.2 Writing the code
Now you are ready to write the code for the
event procedure so that it will do something more than loading a
blank form. The code must be entered between Private Sub.......End Sub. Let's enter the following code
Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Me.Text = "My First
Me.ForeColor = Color.ForestGreen
Me.BackColor = Color.Cyan
The first line of the code will change the
title of the form to My First VB2010 Program, the second line will
change the foreground object to Forest Green( in this case, it is a
label that you insert into the form and change its name to
Foreground) and the last line changes the background to Csyan
color. The equal in the code actually is used to assign something to
the object, like assigning yellow color to the foreground of the
Form1 object (or an instance of Form1). Me is the
name given to the Form1 class. We can also call those lines as
Statements. So, the actions of the program will depend on the
statements entered by the porgrammer.
The output is shown in the windows below:
ere is another example.
Private Sub Button1_Click_1(ByVal sender As
System.Object, ByVal e As System.EventArgs) Handles
Dim name1, name2, name3 As String
name2 = "Georges"
name3 = "Ali"
names are " & name1 & " , " & name2 & " and "
In this example, you insert one command button into the form
and rename its caption as Show Hidden Names. The keyword Dim is to
declare variables name1, name2 and name3 as string, which means they
can only handle text. The function MsgBox is to display the names in
a message box that are joined together by the "&" signs.
The output is shown below:
Copyright 2010 Dr.Liew Voon Kiong . All rights
reserved |Contact: firstname.lastname@example.org [Privacy