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

  • Thread starter Thread starter Nando
  • Start date Start date
N

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!
 
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!
 
bcap said:
To do it in a more "VBA" kind of a way, have the Books collection as a
public member of the Bookshelf class.
Click to expand...

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 said:
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!
Click to expand...

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.
 
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
 
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
 
Terrific, looks good to me!

Nando said:
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
Click to expand...
 
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