ExcelBanter - View Single Post - Avoiding duplication in objects with large commonality

Jamie Collins

(Andrew) wrote ...

I am implementing an object structure which consists of a number of
objects and each of those objects should be accessed via a collection
class.

I'm not sure whether I can do
anything with the "Implements" keyword but it looks like this is more
for creating a common interface rather than common base code.

VBA supports polymorphism via Implements whereas you are looking for
more traditional inheritance which VBA does not support. I have a
standard collection class 'template' from which I change the class
name each time. And, because I have the usual default member and
NewEnum frigs, I have to do this in a text editor else risk losing
them.

In case that last comment made no sense you can 'neaten' your syntax
to

Joints("JointName").JointProperties
Pipes("PipeName").PipeProperties
etc

by making Item the default member of the class. Because this Attribute
property is invisible in VBA, you have to export the class module to a
file, open it in a text editor (e.g. Notepad) and add the magic line:

Public Property Get Item(ByVal Index As Variant) As CColumn
Attribute Item.VB_UserMemId = 0 ' <<<<< magic line
Set Item = m_colColumns.Item(Index)
End Property

(note must be Public - not Friend - and the keyword 'Item' in the
magic line must match the procedure name). While in the text editor,
you may as well add the following, which contains *two* magic lines:

Public Property Get NewEnum() As IUnknown
Attribute NewEnum.VB_UserMemId = -4
Attribute NewEnum.VB_MemberFlags = "40"
Set NewEnum = m_colColumns.[_NewEnum]
End Property

The above allows a For Each loop to be performed on the collection
class. Save in the text editor and re-import the class to the VBA
project.

Jamie.

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