Page 335 - Microsoft Office Excel 2003 Programming Inside Out

Developing Class Modules

The same situation occurs when you execute the second statement. Because a value
wasn’t assigned to Latitude in the temporary variable, the previous value of 47.63 is over-
written by zero, which undoes the change made in the first statement.
There are a couple of ways to avoid this problem. The first and probably best way is to cre­
ate a class rather than use a Type statement. However, if you really want to use the Type
statement, you should create a temporary variable of your own, assign the values to the
structure, and then assign the structure to the property like this:
Dim TempVar As MapCoordinateType
TempVar.Latitude = 47.63 Chapter 14
TempVar.Longitude = 122.13
MicrosoftWay.MapCoordinate = TempVar

Defining Methods

Methods are simply public functions and subroutines. They are free to accept any set of
parameters and return any type of value. They can also access any class-level variable whether
it’s public or private, along with any property routine.
For example, assume that the class held information about a particular product from the
Garden Company. You might create a function that computes the discounted price like this:

Public Function DiscountedPrice (Discount As Currency) As Currency

If Discount >= 0 and Discount < 1.0 Then
DiscountedPrice = MyListPrice * (1 - Discount)
Else
DiscountedPrice = MyListPrice
End If

End Function
This routine verifies that the input parameter is valid by making sure that it’s in the range of
0 to 1 and then computes the discount price accordingly. If the discount value is illegal, the
list price of the item is returned.

Tip Saving Cycles
If you have a choice between using a property routine or a private class-level variable in a
method, use the private class-level variable. Doing that avoids the extra processor cycles
and memory required by the property routine and helps to speed up your application.

309
Part 4: Advanced VBA