Lesson III - Visual Basic Programming and Common Controls
In this lesson we shall discuss the programming method and commonly
used basic controls. Visual Basic is just an improved version of the BASIC
language that has "visual" features like controls and forms to
function better in a Windows environment. To use Visual Basic you must first
have good BASIC programming skills. It is recommended that you learn QBASIC
or BASIC before you proceed to learn Visual Basic - in fact, it is essential
that you do so. The "visual" part consists of forms and controls
which serve as the user interface. Without code, they are just some pretty
eye candy that do nothing at all. Each form, control and module must be
assigned with it's own code in order to function. This code is written in
a slightly different version of BASIC. The most important change from the
standard QBASIC/BASIC is the use and reference of controls. The controls
and their behavior are accessed by using code. Each object (ie. a control)
has it's own properties that define it's behavior. These properties can
be changed by code. The syntax for referring to an object and it's properties
from within the code is as follows : <objectname.type.property>. For
example if I wanted to access the "text" property of a "Text
Box" (a type of control) named "Test1" I would type : Test1.text
. In this case I need not specify the type because there is only one object
with the name "Test1". The code for objects are accessed by double
clicking on them. Now that you know how to refer to objects in your code
we shall proceed to explore the common controls in the ToolBox. Out of the
many controls in the ToolBox, the most commonly used ones Label, Command
Button, Text Box and Image Box. To find out the names of the commands, just
move your cursor over the buttons and wait for a few seconds and the name
of the control will appear.
The Command Button 
The command button is the most used control that is found in almost all
Windows applications. It takes the form of a gray square or rectangle take
looks depressed when clicked. It is used to carry out the associated code
when clicked. To create a command button, click the control button then
drag your cursor on the form. Release the mouse button when you have created
the desired size for the command button. A command button with the text
command1 will appear. You can resize and reposition this button. To access
the properties of this control hit "F4" on the keyboard to bring
up the properties window. Scroll up and down in the properties window. You
will see a property called "Caption". You can change properties
by clicking on the box to the right of the property. Modify the Caption
property. Type in text in the box to the right of the Caption property.
You will notice that the text in the command button changes accordingly.
However this text is just for show and user interface but it serves no programming
purposes. The real name of the command button is access via the "Name"
property. Change this property to define the control's name. This name will
be the object name that will be used for reference in the code.
The Label Control 
The label control is just what it says - a label. It is basically a box
that contains text. To create a label click the label button and then drag
your cursor on the form. A label box will be created. It can be resized
and repositioned. As with the command button, hit "F4" to access
the property window. You will notice that it has different properties from
the command button. All controls have properties that are unique and also
properties that are similar (ie. Caption and Name). In this case, the Caption
property defines the contents of the label. This can be changed by using
code. The text on the label cannot be directly changed by the user.
The Text Box 
The text box produces a similar effect as a label except the text on it
can be directly manipulated by the user. In the properties window, the predefined
text is not controlled by the Caption property. Instead it is controlled
by the Text property. To create a text box follow the same procedure as
when creating a label. It can also be resized and repositioned. The text
box is used to obtain input from the user in the form of text. Text boxes
also contain code for it to operate.
The Image Box 
The image box allows you to insert graphics in bitmap form in your program.
It is created in the same manner as the previous controls and can be resized
and repositioned after creation. VB4 only supports BMP (Windows Bitmap)
files whereas VB5 supports many types from GIFs to JPGs. Hit "F4"
to access the properties box. Look for the "Picture" property.
This property defines the image to be placed within the image box. Click
on the box next to the property to open a "file open" dialog box.
Select the graphic files from here. The image will be placed within the
image box. This graphic will be stored in an *.frx file whereas the code
will be stored in a *.frm file. The *.frx file can grow greatly in size
with the addition of many graphics. Therefore, the file in the Picture property
can also be assign by code as the Image control also has it's own code.
This concludes our first look at Visual Basic and some of it programming
techniques and simple controls. In the next lesson we will construct and
discuss our first program using your knowledge of these simple controls!
Back to Learning Visual Basic.
If you have any comments or questions please write to CrydoVax
(Varian Qua)
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