Cannot iterate through the items in custom class collection (NewEnum())

[Nando]

Hi all! I have created two class modules: Book and Bookshelf. The last one
is implemented as a collection of items of the first one. I have included
the function NewEnum() in the Bookshelf class, so I can iterate through the
elements of the collections using a "For Each" loop. The problem is that
code below comes up with a runtime error '438': "Object doesn't support this
property or method." However this code does work under VB6. What's wrong?!
How can I make it to work under Access XP? The only way I can get it to work
is using the second code "FormV2_Load()"

'This version does not work
Private Sub Form_Load()

Dim MyBookshelf As Bookshelf
Dim Item As Book

Me.List1.RowSourceType = "Value List"

Set MyBookshelf = New Bookshelf

For Each Item In MyBookshelf
Me.List1.AddItem Item.Title & vbTab & Item.ISBN
Next Item

Set Item = Nothing
Set MyBookshelf = Nothing

End Sub

'This version does work
Private Sub FormV2_Load()

Dim MyBookshelf As Bookshelf
Dim Item As Book
Dim c As Long

Me.List1.RowSourceType = "Value List"

Set MyBookshelf = New Bookshelf

For c = 1 To MyBookshelf.Count
Set Item = MyBookshelf.Item(c)
Me.List1.AddItem Item.Title & vbTab & Item.Author & vbTab &
Item.ISBN
Next

Set Item = Nothing
Set MyBookshelf = Nothing

End Sub

Below is the code I included inside Bookshelf to make sure I can use the
"For Each .. Next". This is the collection object enumerator, so it can know
how to iterate through the items in the collection:

' NewEnum must return the IUnknown interface of a
' collection's enumerator.
Public Function NewEnum() As IUnknown
Set NewEnum = mcolEmployees.[_NewEnum]
End Function

I appreciate it your assistance. Thanks!

 

[bcap]

VBA is not VB6! This might help:

http://p2p.wrox.com/topic.asp?TOPIC_ID=26259

To do it in a more "VBA" kind of a way, have the Books collection as a
public member of the Bookshelf class.

 

[Nando]

Thanks bcap! That did it! I'm so happy now. This is a summary of the steps
for any one reading out here:

1) Create your class then export it as text.
2) Delete the class from the project.
3) Edit the text file to implement the procedure attributes, inserting the
line "Attribute NewEnum.VB_UserMemId = -4" right below the function header
"NewEnum()."
4) Re-import the class.

Also I have been playing around a lot and I found it is lot easier to just
use the Class Builder utility under VB6, and import the .CLS files into
Access. Cool stuff! Thanks bcap!

 

[Nando]

To do it in a more "VBA" kind of a way, have the Books collection as a
public member of the Bookshelf class.

How will that look like? I cannot picture it and I'm curious. This is a
sample of the interaction through code:


Dim MyBookshelf As Bookshelf
Dim Item As Book

Me.List1.RowSourceType = "Value List"

Set MyBookshelf = New Bookshelf

For Each Item In MyBookshelf
Me.List1.AddItem Item.Title & vbTab & Item.ISBN
Next Item

Set Item = Nothing
Set MyBookshelf = Nothing

 

[Nando]

Thanks bcap! That did it! I'm so happy now. This is a summary of the steps
for any one reading out here:

1) Create your class then export it as text.
2) Delete the class from the project.
3) Edit the text file to implement the procedure attributes, inserting the
line "Attribute NewEnum.VB_UserMemId = -4" right below the function header
"NewEnum()."
4) Re-import the class.

Also I have been playing around a lot and I found it is lot easier to just
use the Class Builder utility under VB6, and import the .CLS files into
Access. Cool stuff! Thanks bcap!

As a note: I just found out that if you cut and paste the procedures, during
code editing, these member attributes may be lost, so the importing will
have to be done again.

 

[bcap]

Dim MyBookshelf As Bookshelf
Dim Item As Book

Me.List1.RowSourceType = "Value List"

Set MyBookshelf = New Bookshelf

For Each Item In MyBookshelf.Books
Me.List1.AddItem Item.Title & vbTab & Item.ISBN
Next Item

Set Item = Nothing
Set MyBookshelf = Nothing

 

[Nando]

OK, following your recommendation I had to redesign my object oriented
model, so item iteraction makes more sense. I learned a lot on the way and
hopefully I got it right now.

Book 'Class
Title As String
Author As String
ISBN As String

Books 'Class/Collection
Item As Book
Count As Long
Add()
Remove()
NewEnum()

Bookshelf 'Class
Tag As String
Location As String
Books As Books

'Base on this Object Model I was playing to do this iteraction: (Great it
works!)

Private Sub Form_Load()

Dim MyBookshelf As Bookshelf
Dim Item As Book

Set MyBookshelf = New Bookshelf

With MyBookshelf

'add some test
.Tag = "A-D"
.Location = "South window"

.Books.Add "Learn VB in 5 minutes!", "LL. Liar", "1111111111"
.Books.Add "Mastering Access 2009", "MS Press", "2222222222"
.Books.Add "How to buy the best PC", "M. Dell", "3333333333"

'Print the books
For Each Item In MyBookshelf.Books
Debug.Print Item.Title & vbTab & Item.Author & vbTab & Item.ISBN
Next Item
Set Item = Nothing

End With

Set MyBookshelf = Nothing

End Sub

 

[bcap]

Terrific, looks good to me!

OK, following your recommendation I had to redesign my object oriented
model, so item iteraction makes more sense. I learned a lot on the way and
hopefully I got it right now.

Book 'Class
Title As String
Author As String
ISBN As String

Books 'Class/Collection
Item As Book
Count As Long
Add()
Remove()
NewEnum()

Bookshelf 'Class
Tag As String
Location As String
Books As Books

'Base on this Object Model I was playing to do this iteraction: (Great it
works!)

Private Sub Form_Load()

Dim MyBookshelf As Bookshelf
Dim Item As Book

Set MyBookshelf = New Bookshelf

With MyBookshelf

'add some test
.Tag = "A-D"
.Location = "South window"

.Books.Add "Learn VB in 5 minutes!", "LL. Liar", "1111111111"
.Books.Add "Mastering Access 2009", "MS Press", "2222222222"
.Books.Add "How to buy the best PC", "M. Dell", "3333333333"

'Print the books
For Each Item In MyBookshelf.Books
Debug.Print Item.Title & vbTab & Item.Author & vbTab &
Item.ISBN
Next Item
Set Item = Nothing

End With

Set MyBookshelf = Nothing

End Sub

 

[Nando]

Terrific, looks good to me!

Thanks a million!