Chapter 3

Introduction to Visual Basic Environment

Application – another name for a program. Interface – is what appears on the screen when the application is

running. Program Code – is instructions that tells an application’s objects

how to behave. Object Oriented Programming - Uses classes, which are program

code and data, to create objects. Objects- can have visual representation such as a dialog box,

button, Label etc. Event-driven program – when a program runs due to an object

being selected by the user.

A Visual Basic Application

IDE – Integrated Development Environment.◦ Used to create a Visual Basic application

The Visual Basic IDE consists of:◦ Menu Bar◦ Tool Bar◦ Tool Box◦ Project Window◦ Project Explorer Window◦ Properties Window◦ Form Layout Window

The Visual Basic IDE

The Visual Basic IDE

Menu Bar Tool Bar Project Window Project Explorer Window Properties Window Form Layout Window

Visual Basic Environment

Form – is a container object for other objects

Adding Objects to a Form

Objects are added during design time The time during which the applications interface is being

created. Label object is used to display information. Command Button object is something a user can click on.

Objects are added by clicking and moving your mouse over to the screen and dragging it across the form.

Design Time

Properties – defines its appearance, behavior, position, and other attributes.

Each type of objects have many different types of properties.

Object Property Values

Name – identifies an object all names should start with the prefix “lbl”.

Caption – changes the text displayed in the label Font – used to change font style, and size. Alignment – Changes the alignment of text in a label’s

caption (left & right justify and center)

Label Properties

Name – identifies the object. Prefix “cmd”. Cannot be change at runtime.

Caption – Changes the text displayed in the command button.• Example: cmdCancelorDone.Caption = “Done”.

Form Properties Name – identifies an object. Prefix “frm”. Cannot change

during runtime. Caption – changes the text displayed in the title bar.

• Example: frmUserApp.Caption = “My Application”

Command Button Properties

When naming an object, it should start with the appropriate prefix and then be descriptive of the object’s purpose.

Programming Style

Selecting an object is done by simply clicking on it. Resizing by using the drag handle Marquee Selection – Selecting the pointer control and

create a dash box around several objects at one time.

Resizing and Moving Objects

File menu and select the “Save Project” command or clicking on disk icon shortcut key.

First saved – both form and project must be given descriptive names.◦ Save the form using the same name as its Name Property and then

save the project using a descriptive name of the application.

Saving a Project

F5 – start command Run Menu and select run Run icon on the toolbar

Run Time Refers to the time during which application is being

executed. A VB program can be run at any time of its development.

Running a Visual Basic Application

Run Menu – select “End” command. Click the End icon on the Tool Bar.

End Command

Also refer to as Program Contains set of instructions that tells the computer how to

perform specific task. Each line of code is referred to as a statement.

Event Procedures Is a block of code that executes in response to an event. Event (User Event) – is a way in which the user can

interact with an object, such as clicking a button. Specific actions will be taken when the user clicks on the

button.

Application

Container for program code. Code Editor – is the area displaying the form module

Form Module

View Code button View Object button

Display by double-clicking on the form. Display by clicking on the View Code Button in the Project

Explorer. Clicking the button beside the view

code button returns you back to the form.

Code Editor Window

Removes a form from memory and ends the application. Unload statement requires a form name to be unloaded. If the form to be unloaded is the current form, then you

could use Me◦Example:

Unload Me or Unload Form1

Unload Statement

Examples of Unload Statement

Select object name from Object list and then a corresponding event is selected from the Event name.

Adding Event Procedures

Indicates that the procedure cannot be accessed outside of the form module.

Sub declares the procedures End Sub – ends the Sub statement. Body is between Sub and End Sub statements.

Private

The interface and program code of an application are printed by selecting the print command from the file menu

CTRL + P

Removing a Project from the IDE File menu – Select the Remove Project command.

Printing A Project

Assignment – is used to change the value of an object property at run time.

Assignment Statement changes property values using the equal sign (=).

Each Object property can only be assigned a valid property values.

Using Assignment to Change Property Values

Is displayed when typing an object’s name and a dot operator notation mark.

AutoList

Name – Cannot be change during run time by an assignment statement

Caption – Text in double Quote• lblMessage.Caption = “Adios”

Font – has several Subproperties• Size – 0 – 2048

Example: lblMessage.Font.Size = 10• Bold & Italic are True or False

Example: lblMessage.Font.Bold = True• Name – enclosed in double quote

lblMessage.Font.Name = “Arial” Alignment – 0 – left, 1 – right, 2 – center

Valid Values of the label object properties

Event procedures can also be written for form events. The Form_Load event procedure is executed when the

form is loaded into memory.(Application is started or run)

ExamplesPrivate Sub Form_Load() lblSample.Caption = “This text is centered.” lblSample.Alignment = 2End Sub

The Form_Load Event Procedure

Changing object property values in the Form_Load event procedure is alternative to setting property values in the Properties window.

Initializing the form – Setting object properties through the Form_Load event.

Form_Load

Comments – are used to explain and clarify program code for a human reader.

No effect on how the application runs. Single quotation mark (‘) begins a comment Mark code that is ambiguous or misleading. Example: lblSample.Alignment = 0 ‘left justify All programs should state the following:

◦ ‘ Author: Your Name◦ ‘ Date: Current Date◦ ‘ Chapter and Exercises

Commenting Code

File menu – Open Project CTRL + O Open Project Button on the Tool Bar

Opening a Project

Makes programs more interesting Makes it easier to interact with.

Graphics

Located in the Tool Box Used to create Images

Image Control

Name – Use the img prefix when naming and image.

Picture – is used to display a dialog box for selecting the graphic to display in the image area.

Stretch – True or False – True if it has been resized. False otherwise.

Visible – True or False – To display at run time Visible = True. To hide Visible = False.

Properties of an Image

Displays as a box, when added to a form.

Image Object

Go to Property box and select Picture. Click on box on ellipsis.

Stretch should be set to true so image will fit in the image box.

Click event Is when the user clicks on an image object to perform an

action.

Selecting an Image

Built-in arithmetic operators◦ “^” - exponential◦ “*” - multiplication◦ “/” – division◦ “\” – Integer division◦ “Mod” - Modulus◦ “+” - addition◦ “-” - subtraction

Operators and Expressions

Arithmetic operators are used to form expressions. Expression can be anywhere a numeric value is allowed

◦ Example: lblAnswer.Caption = 3.14 * 10^2◦ Expressions are NOT enclosed in quotes.

Expression

Exponentiation Multiplication and Division Left to Right Addition and Subtraction Left to Right You can change order of precedence by using parentheses.

Order of Precedence

Always use parentheses when any ambiguity or maybe questions about the expression.

Programming Style

Visual Basic also has a compiler that translate the program code into separate executable file.

Executable file can be run on any Computer that uses Windows 95 or later.

Visual Basic acts as an interpreter that reads each line of program code as it is entered.

Visual Basic will highlight any errors immediately. Interpreter executes the code line-by-line and displays the

output in the IDE.

Compiler & Interpreter

ALT + Q File menu – Exit

Exiting Visual Basic

Create the program interface first Name all objects before writing and code. Use Object list in Code Editor window to select the object

event procedure.

Visual Basic Programming Guidelines