Fundamentals of GUI Programming

Objectives:At the end of the session, you should be able to:

• describe the guidelines that are used for creating user-friendly graphical user interfaces;

• ascertain steps in creating applications;• define variables and data types; and• construct and execute applications by

correctly following syntax and semantics .

Guidelines for GUI Design

• Give priority to the user• Design for clarity• Design for consistency• Provide visual and audio

feedback• Provide keyboard support• Use of appropriate controls

KEYBOARD Support

Steps in Creating Simple Applications

• Create the User Interface (GUI)• Set the Properties of the

Objects• Enter the appropriate Source

Code• Run the Program

Create the User Create the User InterfaceInterface

Set the Properties of the

Objects

Enter the Source Enter the Source CodeCode

Run the ProgramRun the Program

GUI Controls•Used to interact with the

application.•A control is defined by:

– Property– Event– Method

Property•It refers to the characteristic

or parameter of a control–Control’s properties determine its name, color, size, location and appearance on the screen

Types of Properties• Properties of a control can be classified

into the following categories:– Design time property - This type of property

can be changed only during the design phase of the program.

– Runtime property - This type of property will only take effect when the program is running.

– Design time/Runtime property - This type of property can be changed during the design time as well as during the runtime.

PROPERTIES

TEXT of a LabelBox

TEXT of a

TextBox

BackColor of a FormBackColor of a FormBackColor of a FormBackColor of a Form

Event• It refers to an action that happens

during the program’s execution– clicking of a button, pressing a key,

changing the text of a textbox

Method• It refers to the function of a control• It commands the control on what it

should perform once an event occurs.– open, close, move, refresh

Naming a Visual Basic Control

SYNTAX: <prefix> <content>

Control Prefix Label Box lbl

lblHelloWorld Command Button btn btnExit Text Box txt

txtRemarks Form frm frmProgram

Naming a Visual Basic

Control

Variables

• Variable – a named memory location capable of storing

values based on its definition– Numeric: used to store a value which is

numeric in nature– String: used for storing strings

RULES IN NAMING VARIABLES

1. It must start with an alphabetic character.

2. It can contain letters, numbers and an underscore (_).

3. It should not exceed 255 characters.4. It should not contain any special

character and a space.

Data Types

• Data Type – an element of a variable that verifies the kind of data it can store.– Boolean - Short (9)– Integer - Long (17)– Single - Double– String

** the value of string must be enclosed within “ ”

Variable DeclarationsSYNTAX:

Dim <variablename> as <data type>

OR:

Dim <variablename><suffix>Suffixes:

Integer ( % ) Double ( # )Single ( ! ) Long ( & )String ( $ )

Sample Variable Declarations

Ex 1. X and Y are of integer data type.Dim X as integerDim Y%

Ex 2. Name is of string data type. Dim Name$

The Assignment Statement SYNTAX:

ObjectName.PropertyName = Value

WHERE:

ObjectName – name of the control

PropertyName – property of the control Value - a constant or a variable

Ex: lblDisplay.text = “Hello!”

Assignment StatementExample1: Assign the value “Sophomores”

in the textbox named as Remarks.

ANS: Remarks.Text = “Sophomores”

Example2: Assign the value Num1 in the textbox named txtNum1.

ANS: TxtNum1.Text = Num1

Example3: Delete the text in the textbox named as Remarks.

ANS: Remarks.Text = “ ”