Lesson 4: Writing the Code in VB6

Master VB6 coding techniques to create interactive applications with professional event handling

Key Takeaway

VB6 event procedures are the foundation of interactive applications. Understanding how to structure code, handle events, and perform calculations is essential for creating responsive VB6 programs.

Welcome to Lesson 4 of our Visual Basic 6 Tutorial! In this lesson, you'll learn how to write effective VB6 program code to create interactive applications. We'll cover event procedures, control properties, calculations, and more with practical examples you can implement.

4.1 Introduction to Writing Code in Visual Basic

Each control or object in VB6 can initiate various events. These events are neatly cataloged in the dropdown menu within the code window. To unlock this menu, double-click on an object and pick your preferred event from the procedures' box.

1 Event Categories

Events cover form loading, command button clicks, keyboard key presses, object dragging, and more.

2 Event Procedures

For every event, you must compose an event procedure outlining the actions to be executed.

4.2 Accessing the Code Window

To start writing code for an event procedure, double-click an object to enter the VB code window. For example, if you want to write code for the event of clicking a command button, double-click the command button and enter the codes in the event procedure.

VB6 Code Window
Figure 4.1: The VB6 Code Window

4.3 Structure of an Event Procedure

The structure of an event procedure follows this pattern:

EventProcedure.vb
Private Sub Command1_Click()
    ' VB Statements
End Sub

4.4 Writing VB Statements

You enter the codes in the space between Private Sub Command1_Click and End Sub. The keyword Sub stands for a sub procedure that makes up part of all procedures in a program or module.

Important Syntax

The syntax of Visual Basic's program code resembles the English language, making it relatively easy to learn. Common keywords include Print, If...Then...Else, For...Next, Select Case, End, and Exit Sub.

4.5 Understanding Object Properties

The syntax to set the property of an object or to pass a certain value to it is:

Object.Property

Where Object and Property are separated by a period. For example:

Visibility Control

Label1.Visible = True
Makes Label1 visible

Text Assignment

Text1.Text = "Hello"
Sets textbox content

Component Control

Timer1.Enabled = False
Disables Timer1

4.6 Examples of Event Procedures

Example 4.1: Changing Label Visibility and Text

LabelControl.vb
Private Sub Command1_Click()
    Label1.Visible = False
    Label2.Visible = True
    Text1.Text = "You are correct!"
End Sub

Example 4.2: Updating a Label and Image

ImageControl.vb
Private Sub Command1_Click()
    Label1.Caption = "Welcome"
    Image1.Visible = True
End Sub

Example 4.3: Showing Picture Box and Starting Timer

TimerControl.vb
Private Sub Command1_Click()
    Picture1.Visible = True
    Timer1.Enabled = True
    Label1.Caption = "Start Counting"
End Sub

Example 4.4: Building a Counter

This counter starts counting after the user clicks the command button. We use a label as a counter, two command buttons, and a Timer control.

Timer Control Properties

The Timer's Interval property determines how frequently the timer changes. A value of 1000 represents 1 second. In this example, we set the interval to 100 (0.1 second). The Timer's Enabled property is set to false at design time so the program only starts counting after the user clicks the button.

Counter.vb
Dim n As Integer

Private Sub cmd_StartCount_Click()
    Timer1.Enabled = True
End Sub

Private Sub cmd_Stop_Click()
    Timer1.Enabled = False
End Sub

Private Sub cmd_Reset_Click()
    Lbl_Display.Caption = 0
    n = 0
End Sub

Private Sub Timer1_Timer()
    n = n + 1
    Lbl_Display.Caption = n
End Sub

Counter Simulation:

Counter: 0
Click "Simulate Counter" to start
Counter application
Figure 4.2: Counter Application Interface

Example 4.5: Click and Double Click Events

This program displays a message indicating whether a label was clicked once or twice.

ClickEvents.vb
Private Sub MyLabel_Click()
    MyLabel.Caption = "You Click Me Once"
End Sub

Private Sub MyLabel_DblClick()
    MyLabel.Caption = "You Click Me Twice!"
End Sub

Click Simulation:

Label: CLICK ME
Click the button to simulate single/double click
Click events application
Figure 4.3: Click Events Application

Performing Calculations in Visual Basic

Program code that involves calculations is fairly easy to write, similar to mathematics. However, you need to know the basic arithmetic operators in VB:

Multiplication

Use * instead of ×

Division

Use / instead of ÷

Exponentiation

Use x ^ n for xn

Square Root

Use Sqr(x) for √x

Critical Functions: Val and Str$

Two important functions for arithmetic operations are Val and Str$:

  • Val converts text to a numerical value
  • Str$ converts numerical to a string (text)

Failure to use Val will result in incorrect calculations when working with text inputs.

Example: Type Conversion with Val Function

Without Val Function

WithoutVal.vb
Private Sub Form_Activate()
    Text3.Text = Text1.Text + Text2.Text
End Sub
Output: "12" + "3" = "123" (Wrong)

With Val Function

WithVal.vb
Private Sub Form_Activate()
    Text3.Text = Val(Text1.Text) + Val(Text2.Text)
End Sub
Output: 12 + 3 = 15 (Correct)

Lesson Summary

In this lesson, you've learned essential VB6 coding techniques:

Event Procedures

Mastered the structure and creation of event procedures for various controls

Object Properties

Learned to manipulate properties at runtime to create dynamic interfaces

Timer Control

Implemented a functional counter using the Timer control and event handling

Type Conversion

Understood the critical importance of Val and Str$ functions for calculations

You've now built interactive VB6 applications using proper coding techniques and are ready to explore data types in the next lesson.

Next Lesson

Continue your VB6 journey with Lesson 5: VB Data Types.

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