Word Document Properties

Chapter 9: Working with Arrays and Collections
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Listing 9-7
(continued)
‘ Add an entry with a Key and Before value.
PersonCollection.Add Item, Key, Before
‘ Determine whether there is an After value.
ElseIf After > 0 Then
‘ Add an entry with a Key and After value.
PersonCollection.Add Item, Key, , After
Else
‘ The entry is just an Item and a Key.
PersonCollection.Add Item, Key
End If
Else
‘ Determine whether there is a Before value.
If Before > 0 Then
‘ Add an entry with a Before value.
PersonCollection.Add Item, , Before
‘ Determine whether there is an After value.
ElseIf After > 0 Then
‘ Add an entry with an After value.
PersonCollection.Add Item, , , After
Else
‘ The entry is just an Item.
PersonCollection.Add Item
End If
End If
End Sub
Public Property Get Count() As Long
‘ Return the current collection count.
Count = PersonCollection.Count
End Property
Public Sub Remove(Index As Variant)
‘ Remove the requested item.
PersonCollection.Remove Index
End Sub
Public Property Get Item(Index As Variant) As Person
‘ Return the requested item.
Set Item = PersonCollection.Item(Index)
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Part III: Expanding Your VBA Horizons 
15_046500 ch09.qxp 12/5/06 5:36 PM Page 224

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End Property
Private Sub Class_Initialize()
‘ Initialize the collection.
Set PersonCollection = New Collection
End Sub
Notice that the code begins by creating a 
Collection
object. You could also
use the 
Implements
statement to implement the 
Collection
class, but 
this technique is easier. The 
Class_Initialize
method initializes
PersonCollection
so that other methods can use it.
The 
Add
method is the most complex sub-procedure that you write for a col-
lection in most cases. The reason for the complexity is that this method has
so many optional arguments. In addition, when you supply a 
Before
argu-
ment, you can’t supply an 
After
argument — the two are mutually exclusive.
The code divides the task of determining what to do into a 
Key
or no 
Key
decision. It then decides whether you supplied a 
Before
or 
After
argument,
or neither, and takes the appropriate action. Look through the 
Add
method
code, and you see that each decision results in a different 
Add
method-calling
syntax.
The 
Count
property returns the 
PersonCollection.Count
property. You
never need to add error-handling code to this property because it’s read only.
Never make this property read/write. You don’t want someone using the col-
lection to change the count.
The 
Remove
method makes a direct call to the 
PersonCollection.Remove
method. You could add range checking to this method by using the same
techniques that I use in previous examples. The 
PersonCollection.Remove
method raises an error when you supply an incorrect value. Notice the use of
a 
Variant
for this method so that it can accept a string or an integer as input.
The 
Item
property is also read only. Again, you should never make this prop-
erty read/write. Always use the 
Add
method to add new entries to the collec-
tion. Notice that this method returns an object, so you have to use the 
Set
statement.
Creating a default property
No matter which collection you look at, 
Item
is the default property or func-
tion. Figure 9-3 shows that 
Item
uses a special symbol. The explanation for
Item
in the lower pane of the Object Browser window also says that this is
the default property of the 
Fields
collection. The only problem is that VBA
doesn’t provide a direct method for you to create a default property or
method for your class.
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