Introduction to Visual Basic (VB)
Topics
• 1. What is VB?
• 2. What is Event-Driven?
• 3. What is Object-Orientation? • 4. Objects used in VB
• 5. VB objects naming practice • 6. Files in VB
• 7. OOED Programming process • 8. VB statements
What is VB?
• A windows-based system using objects
responding to events
Event-Driven
• Procedural languages – run from start to finish with no human intervention
– Basic, COBOL, FORTRAN, C
• Event driven languages - waits for an event to occur before taking any action
• Example of event
– The press of a key on the keyboard – Movement of the mouse
– The click of a mouse button
Objects
• Reusable software components that model
items in the real world
– e.g. GPA calculator, Tax calculator
• They are self-contained modules that
Encapsulation
• The capability of an object to hide its
internal workings from other
objects
.
• In VB, programmers does not need to know
what is going on inside the object, but only
need to know how to work with the object’s
properties and methods
Object-Oriented Event-Driven
Programming (OOED)
• OOED uses objects in the program and runs
only after the
Events
occur
• OOED is easier to work with
• Users can combine multiple objects to
Starting VB from your computer
…
• Toolbox
• Project Window useful icons
• Properties windows
• How to Add Controls
• How to Add Code
VB and IDEs
• The VB environment can be used to create and execute programs. • After creating a program, it is necessary to run or execute it to use it.
• Programs can be executed within the VB environment or created as executable files to be run outside of the environment.
• VB uses the term ‘project’ as an analogy to ‘program’
• The VB integrated development environment (IDE) consist of a number of elements:
The VB IDE
Toolbox Pull-down menus Tool bar Form
Properties window
Project window
1
stProject (ShowName)
• A Form
• Three Command Buttons
– Show Name – Click Me – Exit
Forms and Controls as Objects
•
Forms
and
Controls
are two kinds of
objects you may use in VB
• A
form
is a virtual blank space to design
the user interface for a VB application
• The tools that you use to construct the user
interface are
controls
Some popular components
• Textboxes, buttons, and labels are the most popular components. Textboxes hold text - often user input. • Labels are for labeling other components, usually. • Buttons can be “pressed” to fire an event.
• Picture boxes can “hold” images
• comboboxes allow multiple choices.
• Listboxes are like multi-line textboxes, (Textboxes can also be set to be multiline).
Examples of Useful Events
• Form
– Form_Load( ) : used to initialise values in a form before it appears on screen
– Order of all Form Events:
Form_Initialize, Form_Load, Form_Resize, Form_Activate, Form_GotFocus, Form_Unload, Form_Terminate etc
• Command Button
– Command_Click( ) : used to execute statements whenever the button is clicked
• - Other Command Events:
VB objects naming practice:
• Start the name with a standard object abbreviation
– cmd = command button, txt = text box, frm = form.
• Finish the name with a descriptive word of the objects
purpose
• Spaces and special characters are not allowed in an
objects name. (E.g. cmdCancel)
• Examples might be:
Features of Objects
• The programmer can manipulate the object
through the use of three key object features:
Object Properties
• A property is a named attribute of an object.
• Using an analogy to English grammar, if an object is thought of as a noun, then a property may be
thought of as an adjective.
• Used to change the appearance of objects.
• An example of the relationship between objects and properties using an everyday object:
Setting Values of Properties
• During
design time
, properties may be set
in the Properties Window.
– You are in “Design Time” when you are designing the project and adding code
• Some properties may be set or modified
during
run time
.
Object Methods
• A set of predefined activities that an object can carry out. • The syntax for using an objects method is:
– object.method
• A method is a verb that can be carried out by the object.
• For the various VB objects, there are usually several methods already available.
Methods Example
• Real life example
– dog.eat – dog.bark – dog.run
• A Visual Basic example
Object Event
• An action taken by the object when notified by a message
• Or, user actions taken on the object that provokes a response from the object.
• Examples
– Soccer ball: kicking, throwing, holding etc. – Cat: feeding, hitting, calling etc.
– mouse click, form load, or key press. • VB example
Private Sub cmdsubmit_Click() …
Add graphic
• Retrieve your 1
stproject from your disk
• Use image control
• Select a graphic
• Change the size of graphic
– Stretch property of image control
OOED Programming Process
• A six step process for writing an OOED computer program:
1. Define problem. 2. Create interface
3. Develop logic for action objects
4. Write and test code for action objects 5. Test overall project
More Practice
(step 1 to 3 only)
1. Circle problem revisit
– I: radius
– P: calculate circumference, calculate area – O: radius, circumference, area
2. Payroll problem revisit
– I: employee name, pay rate, and hours worked – P: calculate gross pay
Comments
• To explain the purpose of a program, or a statement, a comment statement is added
– For yourself and others
• Any statement beginning with an apostrophe or REM is a comment
VB Statements
• A statement is a reserved word
• Statements are instructions that are built into the Visual Basic language
• Some examples are: End
Option Explicit Private Sub
Visual Basic Help
• There are three types of Help:
– Help menu option
– context-sensitive help – and Auto Help
• In VB 6, Help uses the familiar Internet
Explorer browser interface for the first
two types of help.
Context-Sensitive and Auto
Help
• With context-sensitive help, pressing the
F1 key provides help on whatever item the
cursor is located.
• With Auto Help, VB tries to help you with
a code statement by providing:
– A list of items to complete the statement – Info on the statement you have started