LESSON VISUAL BASIC

WEEK 9 - WEEK11

Objectives

• To continues for the Visual Basic

Naming Controls

This is the string of characters that identifies the control in code. This property can't be an empty string, and you can't have two or more controls on a form with the same name. The special nature of this property is indirectly confirmed by the fact that it appears as (Name) in the Properties window.

When to create a control, Visual Basic assigns it a default name. For example, the first TextBox control that you place on the form is named Text1, the second one is named Text2, and so forth. Similarly, the first Label control is named Label1, and the first CommandButton control is named Command1.

 This default naming scheme frees from having to invent a new, unique name each time you create a control. Notice that the Caption property of Label and CommandButton controls, as well as the Text property of TextBox controls, initially reflect the control's Name property, but the two properties are independent of each other. In fact, just modified the Caption and Text properties of the controls in the Rectangle Demo form without affecting their Name properties.

For an example, we will rename the Text1 through Text4 controls as txtWidth, txtHeight, txtPerimeter, and txtArea respectively. The Command1 control will be renamed cmdEvaluate, and the four Label1 through Label4 controls will be renamed lblWidth, lblHeight, lblPerimeter, and lblArea, respectively. However, please note that Label controls are seldom referred to in code, so in most cases you can leave their names unmodified without affecting the code's readability.

The control classes and their recommended prefixes are shown in below Table:

Control Class	Prefix	Control Class	Prefix
CommandButton	cmd	Data	dat
TextBox	txt	HScrollBar	hsb
Label	lbl	VScrollBar	vsb
PictureBox	pic	DriveListBox	drv
OptionButton	opt	DirListBox	dir
CheckBox	chk	FileListBox	fil
ComboBox	cbo	Line	lin
ListBox	lst	Shape	shp
Timer	tmr	OLE	ole
Frame	fra	Form	frm

Adding Code

This simple program, need to extract the values stored in the txtWidth and txtHeight controls, use them to compute the rectangle's perimeter and area, and assign the results to the txtPerimeter and txtArea controls respectively:

Private Sub cmdEvaluate_Click() ' Declare two floating point variables. Dim reWidth As Double, reHeight As Double ' Extract values from input TextBox controls. reWidth = CDbl(txtWidth.Text) reHeight = CDbl(txtHeight.Text) ' Evaluate results and assign to output text boxes. txtPerimeter.Text = CStr((reWidth + reHeight) * 2) txtArea.Text = CStr(reWidth * reHeight) End Sub