VB 6 Database Programming

1
VB 6 Database Programming

• Chapter 7

2
Chapter 7 Tutorial

• Read and Complete all of Chapter 7

3
Class Modules

• Code Reuse
• Encapsulate code in VB Class Module
• Reuse the class with any form
• Add a few lines of code to create the class
• Set a few properties
• Example we have coded a Data Entry
  (Maintenance) Program for a table in a database
  so lets reuse the same code for any table in any
  database
• Thus the array and loop concepts

4
What is a Class? An Object?

• A Class is a template for something we wish to
  build
• Like a blueprint to build a house (instructions
  only)
• An object is an instance of the class
• The completed house (using the blueprint) is an
  object
• We have instantiated an object from the class

5
PIE (OOP Technology)

• Polymorphism
• Inheritance
• Encapsulation

6
Polymorphism

• We can call a method or a property irrespective
  of the particular ways that a specific object
  implements them
• Different types of objects can perform the same
  kind of action (in different ways)
• Classes have properties and methods

7
Inheritance

• A child object can inherit the functionality of a
  parent object
• An object could share methods common to other
  objects
• An object could contain methods specific to their
  own type
• Create a parent object, then use it as the basis
  for a new object

8
Encapsulation

• Information about the implementation of an object
  is hidden within the class
• Details of how it works are transparent to the
  outside world

9
VB and PIE

• Classes we can create in VB support the concepts
  of Polymorphism and Encapsulation only

10
VB Class Builder

• Handy tool for building a class module
• Add Properties
• Add Methods
• only shows Public Methods if you re-enter the
  Class Builder
• Creates (Private) Variables for each property in
  code
• Creates (Public) Property code to assign values
• Get Read value from variable
• Let / Set Write (assign) value to variable

11
Creating a Class Module
12
Properties

• Data Control Caption (Find)
• Buttons Record Source (Find)
• DBName Match Field (Find)
• FormName
• Label to Update (Record _ of _ )
• Progress Bar
• Record Source
• Tag

13
Methods

• Process Cmd Build Criteria (Find)
• Lock The Controls
• Navigate Buttons
• Update Buttons
• Update Label

14
P 306 Main Form_Activate

• Add the Boolean variable code to prevent the
  Activate from occurring more than once Refer to
  Book Errata approx. page 11
• Note the following corrections in the
• With myDataClass code
• .LabelToUpdate lblRecordCount quotes
• .LockTheControls(True) add this
  line to lock text boxes instead of code in
  errata
• Make sure it is a Public Sub not Private

15
P 314 cmdFind Routine

• Note error
• Dim sResult As String only 1 letter
  el

16
P 330 339Parent / Child Form

• Adding the Data Bound Grid Control at home
  (thanks to Paul Duncan)
• On the VB6 CD or Visual Studio 6 CD navigate to
• Common -gt Tools -gt VB -gt controls
• CtrlA to select entire contents of this
  directory
• Copy all files into C\Windows\System
• Run 2 commands from Start Menu
• regsvr32.exe dbgrid32.ocx
• regedit dbgrid.reg
• Agree to all the doomsday warnings
• Open VB and add components. If Data Bound Grid
  Control is still not there, select Browse and
  select dbgrid32.ocx from C\Windows\System