Page 339 - Microsoft Office Excel 2003 Programming Inside Out

Developing Class Modules

Extending a Simple Class
One of the advantages of using a class to hold related data is that you can easily extend the
class using several different techniques. For example, you can easily add a synonym for an
existing property with a pair of property routines like this:

Public Property Get CommonName() As String

CommonName = Name
Chapter 14
End Property
Public Property Let CommonName(value As String)
Name = value

End Property
These routines are used to return and modify a public class-level variable, thus allowing the
user to manipulate the same value by using two different names.
Another useful technique is to add a method that allows you to initialize all the properties of
the class with a single call. Notice that the following routine takes advantage of the Me key-
word so that anyone using this method would know which parameter affects which property:

Public Sub Init(Name As String, _
ScientificName As String, _
Description As String, _
RetailPrice As Currency, _
WholesaleCost As Currency, _
ProductNumber As Long)
Me.Name = Name
Me.ScientificName = ScientificName
Me.Description = Description
Me.RetailPrice = RetailPrice
Me.WholesaleCost = WholesaleCost
Me.ProductNumber = ProductNumber
End Sub

A Collection Class

It’s often useful to create a collection class to hold a group of objects. This task is made a lot
easier by using the Visual Basic Collection object to store your data. The following code
declares a Collection object variable that’s local to the class. When the class is first instanti­
ated, the Collection object is created, and when the object is destroyed, the Collection object
will also be destroyed.

313
Part 4: Advanced VBA