2. 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
• 9. VB Help
3. What is VB?
• A windows-based system using objects
responding to events
• An objected-oriented event-driven
programming language
4. 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
• Programming in Windows is usually termed
event-driven programming
5. Objects
• Reusable software components that model
items in the real world
– e.g. GPA calculator, Tax calculator
• They are self-contained modules that
combine data and program code which pass
strictly defined messages to one another
6. 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
– How many drivers are mechanics?
7. 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
create new systems or extend existing ones
8. Starting VB from your computer
…
• Toolbox [p. 27]
• Project Window [p. 28] useful icons
• Properties windows [p. 30]
• How to Add Controls [p. 36]
• How to Add Code [p. 39]
• The toolbar icons [p. 43]
9. 1st Project (ShowName)
• A Form
• Three Command Buttons
– Show Name
– Click Me
– Exit
• One Text Box
• One Label
10. 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
– E.g. command button and textbox etc.
11. 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:
– frmMain.BackColor = vbRed
– txtState.Text = ""
12. Features of Objects
• The programmer can manipulate the object
through the use of three key object features:
– properties
– methods
– events
13. 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:
– shirt.color = "Green“
– shirt.launder = "Clean“
14. 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.
– You are in “Run Time” when you click the VCR
Run icon
15. 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.
• Or advanced programmers can create their own
methods.
16. Methods Example
• Real life example
– dog.eat
– dog.bark
– dog.run
• A Visual Basic example
– E.g. frmMain.hide
17. 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()
…
End Sub
18. Files in Visual Basic
• All projects in VB have a .vbp (project) file
and at least one .frm (form file) file.
• Always save .frm files first and then save
project files. Use File|Save or File|Save
as… commands for this purpose or click
Disk icon on toolbar.
• Projects with graphics also have .frx (binary
form) files. They are saved automatically.
• Module files have a .bas extension and are
pure code files.
19. Save files
Important!
Save early.
All three types can and should have
same names.
Eliminate prefix (eg.frm)
20. Add graphic
• Retrieve your 1st project from your disk
• Use image control
• Select a graphic
• Change the size of graphic
– Stretch property of image control
• Save the project
21. Save it
• Use your last name
• Eg. chen.frm, chen.vbp, chen.frx
• Create a folder in your disk composed
of your name
• Copy files to your folder
• Drag the folder to:
• W:appsclassesmist4600homework
Dchentestfile folder
22. 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
6. Document project in writing
23. 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
– O: gross pay
24. 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
• Comments can be added to end of statements
using apostrophe
25. 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
Dim
26. 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.
• You can seek help by selecting Contents,
Index, or Search from the Help menu item
27. 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
– Tips on the type of data you are working with
