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.
Figure 3.1 on the right is
a typical properties window for a form. You can rename the form caption
to any name that you like best. In the properties window, the item
appears at the top part is the object currently selected (in Figure 3.1,
the object selected is Form1). At the bottom part, the items listed in
the left column represent the names of various properties associated
with the selected object while the items listed in the right column
represent the states of the properties. Properties can be set by
highlighting the items in the right column then change them by typing or
selecting the options available.
For example, in order to change the caption, just highlight Form1
under the name Caption and change it to other names. You may also try to
alter the appearance of the form by setting it to 3D or flat. Other things
you can do are to change its foreground and background color, change the
font type and font size, enable or disable, minimize and maximize buttons and
more.
You can also change the
properties at runtime to give special effects such as change of color,
shape, animation effect and so on. For example the following code will
change the form color to red every time the form is loaded. VB uses
hexadecimal system to represent the color. You can check the color codes in
the properties windows which are showed up under ForeColor and BackColor .
Figure 3.1
Example 3.1: Program to change background color
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 Shape to a particular shape at runtime by
writing the following code. This code will change the shape to a circle at
runtime.
Private Sub Form_Load()
Shape1.Shape = 3
End Sub
We are not
going into the details on how to set the properties. However, I would like to
stress a few important points about setting up the properties.
-
You should set the Caption Property of a control clearly so that a user
knows what to do with that command.
- Use a meaningful name for the Name Property because it is easier to write and read the event procedure and
easier to debug or modify the programs later.
-
One more important property is whether to make the control enabled or not.
-
Finally, you must also considering making the control visible or invisible
at runtime, or when should it become visible or invisible.
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. Just like text fields in websites, powered not by Windows, but typically linux web hosting platforms like iPage, these fields collect user input.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:\VB
program\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:\VB
program\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.
Example 3.7
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
Figure
3.4 The Drive List Box
3.2.11 The Directory List Box
The Directory List Box is for
displaying the list of directories or folders in a selected drive. When you place
this control into the form and run the program, you will be able to select
different directories from a selected drive in your computer as shown in Figure
3.5
Figure 3.5 The Directory List Box
3.2.12 The File List Box
The File List Box is for displaying
the list of files in a selected directory or folder. When you place this control
into the form and run the program, you will be able to shown the list of files in a
selected directory as shown in Figure 3.6
Figure 3.6 The File List Box
You can coordinate the Drive List
Box, the Directory List Box and the File List Box to search for the files you
want. The procedure will be discussed in later lessons.
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