CS 4448 - Fall 1998
Object-Oriented Programming and Design
Talk 11.3
by
Seth Sanusi

Object Oriented Progamming in Visual Basic^TM

1. History of Visual Basic
   • Modelled after BASIC
   • Developed for Arts and Sciences Students who didn't have in depth programming skills. - "Beginner's All-purpose Symbolic Instruction Code"
   • Objetc Oriented Design first appeared in Version 4.0 for the Windows OS.
   • New OO features in each new version
   • Current Version is 6.0 Released in September 1998
   • Variants of VB:
     • Visual Basic For Applications - MS Office, Visio products - essentially a custom macro language.
     • VBScript - web pages.
2. VB Objects
   • Composed of
     1. Methods
     2. Properties
     3. Events
3. VB Classes
   • Have methods - Functions and Procedures
   • Properties - based on read / write
     • Let - to assign a value to a property
     • Get - to get a value from a property
   • Events - clicks, mouse events, keyboard etc.
4. OOP features in VB
   • Reuse: Class modules, ActiveX controls, ActiveX DLL's, standard OCXs
   • Encapsulations: Hiding of attributes via public and private conventions - just like C++
   • Polymorphism: Common methods throughout objects. Example - Print method works on an Excel Spreadsheet, Word Documents and User Forms. Most languages use inheritance to implement Polymorphism. VB uses the multiple interface approach of COM (Component Object Model).
   • Inheritance / Multiple Inheritance: VB does not support multiple inheritance directly. Inheritance features can be "added-in" to VB via third party ActiveX controls like ClassAssist from Sheridan Software. VB does not implement inheritance for sake of:
     • Simplicity
     • Speed
     • Robustness
5. Common Uses of OOP in VB
   • Wrappers for the WIN32 API
   • Wrappers for I/O to the Windows Registry
   • Database Access - RDO / DAO / ADO encapsulation
6. VB OOP conventions
   • "count the dots" for faster code
     With Command1
     .height = 100
     .width = 200
     End With
     
   • setting objects to temporary ones
     Dim obj As New CommandButton
     Set obj = Form1.Command1
     
     
7. Error Handling as an Object
   • VB uses an Err object to deal with Errors
   • Programmers can raise Errors and catch them
   • Trappable Erors have a description property and Error Numbers.
   • Example:

     Dim Msg
     ' If an error occurs, construct an error message
     On Error Resume Next	' Defer error handling.
     Err.Clear
     Err.Raise 6	' Generate an "Overflow" error.
     ' Check for error, then show message.
     If Err.Number <> 0 Then
     	Msg = "Error # " & Str(Err.Number) & " was generated by " _
     			& Err.Source & Chr(13) & Err.Description
     	MsgBox Msg, , "Error", Err.Helpfile, Err.HelpContext
     End If

8. Summary:
   • Visual Basic is a Rapid Application Development environment that supports OOP paradigms except for multiple inheritance.
   • Online Slides can be viewed here: http://ucsu.colorado.edu/~sanusis/oop/vb/sld001.htm

Hyperlinks:

• OO Specific VB Links:
  • Benefits of Good OO Design in VB
  • Providing Polymorphism by Implementing Interfaces
  • VBA Questions and Answers
  • Visual Basic as an Object Oriented Language
  • Object Oriented Language : Visual Basic
  • Visual Basic Corner
• General Visual Basic Links (Some of the best on the Web)
  • Visual Basic:

1. Carl And Gary's VB page - the most popular one on the web
   1. Beginner's links
2. Microsoft's VB page
3. Microsoft's knowledge base
4. Seth's VB page - with sample VB source code for all Numerical Comp assignments
5. VB Online magazine
6. Visual Basic Programmer's Journal
   1. 101 Tech Tips, 7th Edition (Word Format)
7. VB links on the internet
8. Download.com 's ActiveX components. More ActiveX components than you can shake a stick at.
9. Rap with other VB developers for help
10. Newsgroups - ask for help, find a job, make fun of other programmers:
    1. The VB Misc newsgroup
    2. The VB database newsgroup

Copyright © University of Colorado. All rights reserved.
Revised: Novemeber 23, 1998