Visio VBA: Invalid Parameter in Nested Loop - vba

Question

In Microsoft Visio Professional 2010 I've isolated the error I've been getting to this little code snippet. On the page is a container holding 2 shapes and I want to iterate through those shapes within another loop. But I keep getting an invalid parameter error.
My attempt at a solution is the top block, but it only works with the same definition for the inner loop. It seems like something is changing during the 2nd iteration of the outer loop, but I'm not sure. I feel it has to do with the way a For Each loop is defined.
Sub Nested_Loop_Error()
Dim a As Variant
Dim b As Variant
Dim lngs() As Long
'This Works
lngs = ActiveDocument.Pages(1).Shapes.ItemFromID(1).ContainerProperties.GetMemberShapes(visContainerFlagsDefault)
For a = 0 To 1
For Each b In lngs
'Do nothing
Next b
Next a
'This does not work
For a = 0 To 1
For Each b In ActiveDocument.Pages(1).Shapes.ItemFromID(1).ContainerProperties.GetMemberShapes(visContainerFlagsDefault)
MsgBox "In Loop for a=" & a
Next b
Next a
End Sub
Edit:
I've been playing around with it and got it to work, but what I'm really interested in is why it works. The 2nd block of code fails when a=1, giving an invalid parameter in the line docMyDoc.Pages...
The following is the code showing the difference of using a variant or a document variable to define the ActiveDocument within the loop. Using the debugger I can't see a difference in how docMyDoc or varMyDoc are defined.
Sub Nested_Loop_Error2()
Dim a As Variant
Dim b As Variant
Dim docMyDoc As Visio.Document
Dim varMyDoc As Variant
'This works
For a = 0 To 1
Set varMyDoc = ActiveDocument
For Each b In varMyDoc.Pages(1).Shapes.ItemFromID(1).ContainerProperties.GetMemberShapes(visContainerFlagsDefault)
MsgBox "Using variant, a=" & a
Next b
Next a
'This does not work
For a = 0 To 1
Set docMyDoc = ActiveDocument
For Each b In docMyDoc.Pages(1).Shapes.ItemFromID(1).ContainerProperties.GetMemberShapes(visContainerFlagsDefault)
MsgBox "Using document, a=" & a
Next b
Next a
End Sub

Answer 1

Using the Variant type doesn't help the compiler much: The variable called "b" should be of type Long, and the "a" variable of type Integer.
This said, you're not using the "a" variable but to repeat twice what you do in the inner loop (Msgbox), but nothing else changes.
Moreover, you need to reference the shape whose ID is b, that you're not doing.
And another tip: don't name variables after their type, but after their semantics.
I think that what you intended to do is something like the example in GetMemberShapes method's reference in MSDN:
Sub Nested_Loop()
Dim lngMemberID as Long
Dim vsoShape as Visio.Shape
Dim j as Integer
For j = 0 to 1
For Each lngMemberID In ActiveDocument.Pages(1).Shapes(1).ContainerProperties.GetMemberShapes(visContainerFlagsDefault)
Set vsoShape = ActivePage.Shapes.ItemFromID(memberID)
Debug.Print vsoShape.ID
Next lngMemberID
Next j
End Sub
Here, your vsoShape variable will refer first to one, then to the other of your shapes. And it will work even if you have more shapes in your page.
That's the good thing of Collections and the For Each loop: Collections are special objects made up as a list of other objects. They have their own methods, as Item, or Count, and shortcuts, like using a number between parenthesis to retrieve an individual object from the collection (as in Pages(1)).
What you do with For Each is to iterate through all the objects in the collection (or all the values in an array).
For your purposes, I'd try the following general structure:
dim oPage as Visio.Page
dim oShape as Visio.Shape
dim oInnerShape as Visio.Shape
For each oPage In ActiveDocument.Pages
For each oShape in oPage.Shapes
If oShape.Master.Name = "xxx" Then ' You can check the type of the shape
For each oInnerShape In oShape
' set and compute width and height
Next oInnerShape
' set and compute width and height of the containing shape
End If
Next oShape
' Rearrange shapes
Next oPage
You can construct an array storing the shape IDs, width and height, while iterating through the shapes, then use that array to rearrange the shapes.
Regards,

Answer 2

I don't have Visio on my computer but are you certain that the first nested loop worked?
I have doubt in lngs = ActiveDocument.Pages(1)... with Dim lngs() As Long:
Excel VBA will throw "Type mismatch" error with trying to store arr = Array(1,2) with Dim arr() As Long. Better off Dim lngs As Variant even if you know it's an array of Long being returned.
The second nested loop works in theory.