CHAPTER 1: INTRODUCTION TO THE VISUAL BASIC

LANGUAGE AND ENVIRONMENT

•Understand what is an object•Learn the properties, methods and events that correspond with an object•Learn the use of the Properties Window

Lesson 4 – Objects: Properties, Methods and

EventsOBJECTIVES

Introduction

Objects are a distinct unit in a program that has a

certain characteristics and can perform certain actions.

Everything in Visual Basic revolves around what is

called as OBJECTS.

Caption Property

Back Color Property

OBJECT PROPERTIESObjects have PROPERTIES, just like a real-world

object, properties determines what physical appearance your object will look like. You can

change the different properties of each objects.

The format for using Properties in an object is:

ObjectName.Property=Value

Object Name = Name of the object with the properties to change

Property = attribute you want to change

Value = New data of the property

EXAMPLE

Form1.Caption=“Welcome”

ObjectName

Property

Value

Properties Window

• You can also change the Property of an object at design time by using the Properties Window in Visual Basic.

OBJECT METHODSObjects can also perform functions of their own.

The whole point of creating objects is that objects does something useful. This additional

functions are known as METHODS. This allows the objects to perform certain actions.

The format for using Properties in an object is:

ObjectName.Method Value

Object Name = Name of the object with the properties to change

Method = action to perform

Value = Optional parameters or data you can add

EXAMPLE

Form1.Show

ObjectName

Method

EXAMPLE

Combo1.AddItem “IV-Malory”

ObjectName

To add data to a ComboBox we can use the methods optional parameter

Properties or Methods are

separated from the object by using a dot

Method

Optional Parameter/value

USING THE FORMThe form is the basic repository for all you controls, this is were you add all those controls when you design the user

interface. A program can have one or more forms. The form that first appear when you run you program is called

the startup form.

You can change the order of the startup of each form by:

1. Clicking Project from the menu bar

2. Select Project1 Properties

3. The Project Properties will appear

4. Click the Startup Object combo box

5. Select from the list of forms

6. Then click the OK button

USING THE PROPERTIES WINDOW

Each form and control has properties assigned to it by default when you start up a new project. There are two ways to display the properties of an object. The first way is to click on the object (form or control) in the form window. Then, click on the Properties Window or the Properties Window button in the tool bar. The second way is to first click on the Properties Window. The select the object from the Object box in the Properties Window.

Properties can be viewed in two ways: • Alphabetic• Categorized

THE PROPERTIES WINDOW

Each object has a set of attributes, called properties, that determine its appearance and behavior

The Properties window exposes the object’s properties to the programmer

The Properties window includes an Object box and a Properties list

The Properties window can be used to change a property of an object

THE PROPERTIES WINDOW

Properties window showing the properties of the Form1.vb file object

PROPERTIES OF THE WINDOWS FORM OBJECT

The Windows Form object has a set of properties

Properties of the Windows Form object will appear in the Properties window when you select the Windows Form object in the designer window

PROPERTIES OF THE WINDOWS FORM OBJECT

Important properties of the Windows Form object:Name propertyText propertyStartPosition propertySize propertyBackgroundImage property

SETTING PROPERTIES AT RUN TIMEYou can also set or modify properties

while your application is running . To do this, you must write some code. The

code format is:

ObjectName.Property = NewValueSuch a format is referred to as dot

notation. For example, to change the BackColor property of a form name

Form1, we’d type:

Form1.BackColor = vbBlue

HOW NAMES ARE USED IN OBJECT EVENTSThe names you assign to objects are used by Visual Basic to set up a

framework of event-driven procedures for you to add code to. The format for

each of these subroutines (all object procedures in VB are subroutines) is:

Sub ObjectName_Event (Optional Arguments)

End Sub

VB provides the Sub line with its arguments (if any) and the End Sub

statement. You provide any needed code.

TRIGGERING EVENTS ON FORM

Several form events will fire starting with the moment of creation. Each has its own purpose and triggers in a

certain order. When the Form is first created, an initialize event will occur, followed by Load, Resize, and Paint.

1. Start VB and create a new project

2. Double-click the form

3. The Code Window will appear, by default you’ll be in the Load event procedure, click on the events combo box, scroll through and select the Click event.

4. You’ll now have two event procedure (Load and Click)

5. Click inside the Form_Click event and type the following statement

6. Your code window should look like the one in the next slide.

Private Sub Form_Click()Msg “Welcome to Malory”

End Sub

Event Procedure

Program Statement

Properties

Description

Caption Changes the caption of the title bar in the form Window.

Appearance Changes the 3D or Flat appearance of the form

BackColor Changes the form background color

Font Changes the Font style of the form

Enable Sets True of False boolean data, disables and enable the form

Picture Puts a picture on the form

Visible Hide or unhide the form by setting it True or False

ForeColor Changes the color of the text

Events DescriptionLoad Triggers once the program starts

Unload Triggers once the program exits

Activate Triggers once the form is active

Click Triggers once the form is click

Double Click Triggers once the form is double click

Terminate Like Initialize, this event will only occur during the existing of the Form. It won’t fire if the program is terminated abnormally

Initialize This event occurs only once when the Form is created. It will not fire again unless the Form is Unloaded and Loaded again

Methods DescriptionHide Hides the active form

Unhide Unhide the active form

Print Use to print text on the form

Cls Clear any picture on the form

IV-MALORYSubmitted by: Group 4