VBA - How to add a collection to a collection of collections

Question

I am trying to create code to represent a form document using VBA in Word 2007. I have created classes to represent Section, QuestionSet and Question.

So I have 15 Sections. I have created a function to create each 'Section' Object add it to the 'Sections' Collection then destroy the object, the result being that the objects remain persistent in the collection (or something).

Is it possible to use the same method to add collections to collections or would I have to define each collection explictly?

Code in Module:

Public Sections As Collection

Function DefineSection(ByVal SectionName As String)

    Set Section = New clsSection
    Section.myName = SectionName
    Sections.Add Section, SectionName

End Function


Function DefineQuestionSet(ByVal SectionName As String, ByVal Name As String, ByVal NoOfQuestions As Integer, ByVal IsMutuallyExclusive As Boolean, Optional ByVal DependentOnSection As String)

    Dim Qsets As Collection

    Set Qsets = New Collection
    Set QuestionSet = New clsQuestionSet

    QuestionSet.Name = Name
    QuestionSet.NoOfQuestions = NoOfQuestions
    QuestionSet.MutuallyExclusive = IsMutuallyExclusive

    If Not (DependentOnSection) = "" Then
        QuestionSet.DependentOnSection = DependentOnSection
    End If

    Qsets.Add QuestionSet
    Sections.Item(SectionName).Add Qsets

End Function

Then this is called via:

Sub Initilise()

    Set Sections = New Collection

    DefineSection "PersonalDetails"
    DefineQuestionSet "PersonalDetails", "PersonalDetails", 29, False

End Sub

Answer 1

Yes. You can absolutely add collections to collections to collections ad infinitum. The code you have posted looks like it should work just from glancing through it. Are you having specific problems?

UPDATE: VBA only passes around references to objects. If you explicitly destroy an object after assigning it to a collection (eg, Set myObj = Nothing) then you will also be destroying the object inside the collection.

[EDIT]: Apparently this is not true. From this website (first linked by Stevo in the comments):

In order to use collections to manage class objects, you must do the following:

• Create an instance of the class
• Set the properties and methods of the class
• Add the class to a public collection
• Unload the instance of the class

You might expect that unloading the instance of the class results in the class being closed and terminated. However, the class object persists because you add it to a collection, which then owns the reference to the class. This is a very powerful technique that allows you to control object references through a collection; the class object does not terminate until you remove it from the collection.

UPDATE: There's no reason why you can't add a collection to an object. You just need the class your object is instantiated from to support such a method. For example, in your clsSection class module you need an Add method which adds objects passed to it to a collection stored in the clsSection:

Private QSetsColl As Collection

Public Sub Add(QSets As Object)
    If QSetsColl Is Nothing Then Set QSetsColl = New Collection
    QSetsColl.Add QSets
End Sub

Answer 2

Try this simple example:

Private Sub CommandButton1_Click()

    Dim masterCollection As New collection
    masterCollection.Add "first key", createDetailCollection()
    masterCollection.Add "second key", createDetailCollection()
    masterCollection.Add "third key", createDetailCollection()

End Sub

The follow function return a initializated collection

Function createDetailCollection()
    Dim collection As New collection
    createCollection = collezioneBuy
End Function

Answer 3

I think I have the answer now, but if someone could clarify that would be helpful.

I think what the code is doing is trying to add a collection to an object - which obviously won't work. So I need to create a collection which I can add the object AND the collection to. etc.