Lesson 3-Working With Controls

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3.1 The Control Properties

Before writing an event procedure for the control to response to an event, you have to set certain properties for the control to determine its appearance and how will it work with the event procedure. You can set the properties of the controls in the properties window or at runtime.

You can also change the properties at runtime to give special effects such as change of color, shape, animation effect and so on. Example 3.1 show the code that will change the form color to red every time the form is loaded. VB uses the hexadecimal system to represent the color. You can check the color codes in the properties windows which are showing up under ForeColor and BackColor .

Example 3.1: Program to change background color

This example changes the background colour of the form using the BackColor property.

Private Sub Form_Load()
Form1.Show
Form1.BackColor = &H000000FF&
End Sub

Example 3.2: Program to change shape

This example is to change the control's Shape using the Shape property. This code will change the shape to a circle at runtime.

Private Sub  Form_Load()
Shape1.Shape = 3 
End Sub

3.2 Handling some of the common controls

Figure 3.2 below is the VB6 toolbox that shows the basic controls.

Figure 3.2: Toolbox

3.2.1 The Text Box

The text box is the standard control for accepting input from the user as well as to display the output. It can handle string (text) and numeric data but not images or pictures.String in a text box can be converted to a numeric data by using the function Val(text). The following example illustrates a simple program that processes the input from the user. 

Example 3.3

In this program, two text boxes are inserted into the form together with a few labels. The two text boxes are used to accept inputs from the user and one of the labels will be used to display the sum of two numbers that are entered into the two text boxes. Besides, a command button is also programmed to calculate the sum of the two numbers using the plus operator. The program use creates a variable sum to accept the summation of values from text box 1 and text box 2.The procedure to calculate and to display the output on the label is shown below. The output is shown in Figure 3.3

Private Sub  Command1_Click()
'To add the values in text box 1 and text box 2
Sum = Val(Text1.Text) +Val(Text2.Text)
'To display the answer on label 1
Label1.Caption = Sum
End Sub

Figure 3.3

3.2.2 The Label

The label is a very useful control for Visual Basic, as it is not only used to provide instructions and guides to the users, it can also be used to display outputs. One of its most important properties is Caption. Using the syntax label.Caption, it can display text and numeric data . You can change its caption in the properties window and also at runtime.  Please refer to Example 3.1 and Figure 3.1 for the usage of label.

3.2.3 The Command Button 

The command button is one of the most important controls as it is used to execute commands. It displays an illusion that the button is pressed when the user click on it. The most common event associated with the command button is the Click event, and the syntax for the procedure is

Private Sub Command1_Click ()
Statements
End Sub

3.2.4 The Picture Box 

The Picture Box is one of the controls that is used to handle graphics. You can load a picture at design phase by clicking on the picture item in the properties window and select the picture from the selected folder. You can also load the picture at runtime using the LoadPicture method. For example, the statement will load the picture grape.gif into the picture box.

Picture1.Picture=LoadPicture ("C:\VBprogram\Images\grape.gif")

You will learn more about the picture box in future lessons. The image in the picture box is not resizable.

3.2.5 The Image Box

The Image Box is another control that handles images and pictures. It functions almost identically to the picture box. However, there is one major difference, the image in an Image Box is stretchable, which means it can be resized. This feature is not available in the Picture Box. Similar to the Picture Box, it can also use the LoadPicture method to load the picture. For example, the statement loads the picture grape.gif into the image box.

Image1.Picture=LoadPicture ("C:\VBprogram\Images\grape.gif")

3.2.6 The List Box

The function of the List Box is to present a list of items where the user can click and select the items from the list. In order to add items to the list, we can use the AddItem method. For example, if you wish to add a number of items to list box 1, you can key in the following statements

Example 3.4

Private Sub Form_Load ( )
List1.AddItem "Lesson1"
List1.AddItem "Lesson2"
List1.AddItem "Lesson3"
List1.AddItem "Lesson4"

End Sub

The items in the list box can be identified by the ListIndex property, the value of the ListIndex for the first item is 0, the second item has a ListIndex 1, and the third item has a ListIndex 2 and so on

3.2.7 The Combo Box 

The function of the Combo Box is also to present a list of items where the user can click and select the items from the list. However, the user needs to click on the small arrowhead on the right of the combo box to see the items which are presented in a drop-down list. In order to add items to the list, you can also use the AddItem method. For example, if you wish to add a number of items to Combo box 1, you can key in the following statements

Example 3.5

Private Sub Form_Load ( )

Combo1.AddItem "Item1"
Combo1.AddItem "Item2"
Combo1.AddItem "Item3"
Combo1.AddItem "Item4"

End Sub

3.2.8 The Check Box

The Check Box control lets the user  selects or unselects an option. When the Check Box is checked, its value is set to 1 and when it is unchecked, the value is set to 0.  You can include the statements Check1.Value=1 to mark the Check Box and Check1.Value=0 to unmark the Check Box, as well as  use them to initiate certain actions. For example, the program will change the background color of the form to red when the check box is unchecked and it will change to blue when the check box is checked.  You will learn about the conditional statement If….Then….Elesif in later lesson. VbRed and vbBlue are color constants and BackColor is the background color property of the form.

Example 3.6

Private Sub Command1_Click()
If Check1.Value = 1 And Check2.Value = 0 Then
MsgBox "Apple is selected"
ElseIf Check2.Value = 1 And Check1.Value = 0 Then
MsgBox "Orange is selected"
Else
MsgBox "All are selected"
End If

End Sub

3.2.9 The Option Box

 The Option Box control also lets the user selects one of the choices. However, two or more Option Boxes must work together because as one of the Option Boxes is selected, the other Option Boxes will be unselected. In fact, only one Option Box can be selected at one time. When an option box is selected, its value is set to “True” and when it is unselected; its value is set to “False”. In the following example, the shape control is placed in the form together with six Option Boxes. When the user clicks on different option boxes, different shapes will appear. The values of the shape control are 0, 1, and 2,3,4,5 which will make it appear as a rectangle, a square, an oval shape, a rounded rectangle and a rounded square respectively.

Private Sub Option1_Click ( )
Shape1.Shape = 0
End Sub

Private Sub Option2_Click()
Shape1.Shape = 1

End Sub

Private Sub Option3_Click()
Shape1.Shape = 2
End Sub

Private Sub Option4_Click()
Shape1.Shape = 3
End Sub

Private Sub Option5_Click()
Shape1.Shape = 4
End Sub

Private Sub Option6_Click()
Shape1.Shape = 5
End Sub

3.2.10 The Drive List Box

The Drive ListBox is for displaying a list of drives available in your computer. When you place this control into the form and run the program, you will be able to select different drives from your computer as shown in Figure 3.4