Is it possible to access a parent property from a child that is in a collection?

Question

I've researched as much as I can and never found a definitive answer on this for VBA.

This older StackOverflow post has almost everything, but not quite. VBA Classes - How to have a class hold additional classes

Bottom line - I have a class CClock, which is parent to a Collection of CContacts, which is parent to a CContact.

Is there any way to get at a property of the CClock class from a CContact. So something like Debug.Print , clsContact.Parent.Parent.Lawyer in the code below?

I've tried setting the parents as I thought they should be but get the below error almost immediately at Set clsClock = New CClock. When I follow the code it goes to class terminate event in the Contacts collection, which I can't figure out. (Although that is probably why the error below comes up.)

91 - Object Variable or With Variable not set

The various classes and a quick test rig are below (all based on Dick Kusleika's post in the link.) Thanks.

(Edit- added the test routine, whooopsy)

Sub test()

    Dim i As Long, j As Long
    Dim clsClocks As CClocks
    Dim clsClock As CClock
    Dim clsContact As CContact

    Set clsClocks = New CClocks

    For i = 1 To 3
        Set clsClock = New CClock
        clsClock.Lawyer = "lawyer " & i
        For j = 1 To 3
            Set clsContact = New CContact
            clsContact.ContactName = "Business Contact " & i & "-" & j
            clsClock.Contacts.Add clsContact
        Next j
        clsClocks.Add clsClock
    Next i

    For i = 1 To 2
        Set clsContact = New CContact
        clsContact.ContactName = "Business Contact 66" & "-" & i
        clsClocks(2).Contacts.Add clsContact
    Next i

    'write the data backout again
    For Each clsClock In clsClocks
        Debug.Print clsClock.Lawyer
        For Each clsContact In clsClock.Contacts
            Debug.Print , clsContact.ContactName
            Debug.Print , clsContact.Parent.Parent.Lawyer

        Next clsContact
    Next clsClock


End Sub

Clas CClocks

'CClocks
Option Explicit
Private mcolClocks As Collection
Private Sub Class_Initialize()
    Set mcolClocks = New Collection
End Sub
Private Sub Class_Terminate()
    Set mcolClocks = Nothing
End Sub
Public Property Get NewEnum() As IUnknown
    Set NewEnum = mcolClocks.[_NewEnum]
End Property
Public Sub Add(clsClock As CClock)
    If clsClock.ClockID = 0 Then
        clsClock.ClockID = Me.Count + 1
    End If

    Set clsClock.Parent = Me
    mcolClocks.Add clsClock, CStr(clsClock.ClockID)
End Sub
Public Property Get Clock(vItem As Variant) As CClock
    Set Clock = mcolClocks.Item(vItem)
End Property
Public Property Get Count() As Long
    Count = mcolClocks.Count
End Property
Public Sub Remove(vItem As Variant)
        clsClock.Remove vItem
End Sub
Public Sub Clear()
        Set clsClock = New Collection
End Sub

Class CClock

'CClock
Private mlClockID As Long
Private msLawyer As String
Private mlParentPtr As Long
Private mclsContacts As CContacts
Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" _
    (dest As Any, Source As Any, ByVal bytes As Long)
Public Property Set Contacts(ByVal clsContacts As CContacts): Set mclsContacts = clsContacts: End Property
Public Property Get Contacts() As CContacts: Set Contacts = mclsContacts: End Property
Public Property Let ClockID(ByVal lClockID As Long): mlClockID = lClockID: End Property
Public Property Get ClockID() As Long: ClockID = mlClockID: End Property
Public Property Let Lawyer(ByVal sLawyer As String): msLawyer = sLawyer: End Property
Public Property Get Lawyer() As String: Lawyer = msLawyer: End Property
Public Property Get Parent() As CClocks: Set Parent = ObjFromPtr(mlParentPtr): End Property
Public Property Set Parent(obj As CClocks): mlParentPtr = ObjPtr(obj): End Property
Private Function ObjFromPtr(ByVal pObj As Long) As Object
    Dim obj As Object
    CopyMemory obj, pObj, 4
    Set ObjFromPtr = obj
    ' manually destroy the temporary object variable
    ' (if you omit this step you'll get a GPF!)
    CopyMemory obj, 0&, 4
End Function
Private Sub Class_Initialize()
    Set mclsContacts = New CContacts
    Set Me.Contacts.Parent = Me
End Sub
Private Sub Class_Terminate()
    Set mclsContacts = Nothing
End Sub
'CContacts
Option Explicit
Private mcolContacts As Collection
Private mlParentPtr As Long
Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" _
    (dest As Any, Source As Any, ByVal bytes As Long)
Public Property Get Parent() As CClock: Set Parent = ObjFromPtr(mlParentPtr): End Property
Private Sub Class_Initialize()
    Set mcolContacts = New Collection
End Sub
Private Sub Class_Terminate()
    Set mcolContacts = Nothing
End Sub
Public Property Get NewEnum() As IUnknown
    Set NewEnum = mcolContacts.[_NewEnum]
End Property
Public Sub Add(clsContact As CContact)
    If clsContact.ContactID = 0 Then
        clsContact.ContactID = Me.Count + 1
    End If
    Set clsContact.Parent = Me
    mcolContacts.Add clsContact, CStr(clsContact.ContactID)
End Sub
Public Property Get Clock(vItem As Variant) As CContact
    Set Clock = mcolContacts.Item(vItem)
End Property
Public Property Get Count() As Long
    Count = mcolContacts.Count
End Property
Public Sub Remove(vItem As Variant)
        clsContact.Remove vItem
End Sub
Public Sub Clear()
        Set clsContact = New Colletion
End Sub
Private Function ObjFromPtr(ByVal pObj As Long) As Object
    Dim obj As Object
    CopyMemory obj, pObj, 4
    Set ObjFromPtr = obj
    ' manually destroy the temporary object variable
    ' (if you omit this step you'll get a GPF!)
    CopyMemory obj, 0&, 4
End Function

Class CContact

'CContact
Private mlContactID As Long
Private msContactName As String
Private mlParentPtr As Long
Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" _
    (dest As Any, Source As Any, ByVal bytes As Long)

Public Property Let ContactID(ByVal lContactID As Long): mlContactID = lContactID: End Property
Public Property Get ContactID() As Long: ContactID = mlContactID: End Property
Public Property Let ContactName(ByVal sContactName As String): msContactName = sContactName: End Property
Public Property Get ContactName() As String: ContactName = msContactName: End Property
Public Property Get Parent() As CContacts: Set Parent = ObjFromPtr(mlParentPtr): End Property
Public Property Set Parent(obj As CContacts): mlParentPtr = ObjPtr(obj): End Property
Private Function ObjFromPtr(ByVal pObj As Long) As Object
    Dim obj As Object
    CopyMemory obj, pObj, 4
    Set ObjFromPtr = obj
    ' manually destroy the temporary object variable
    ' (if you omit this step you'll get a GPF!)
    CopyMemory obj, 0&, 4
End Function

Answer 1

If you figure out how to access the kernel memory to do this, let me know. Take a look at the source code of vbWatchDog for some hints. I have been studying it to try to gain access to the call stack. I haven't figured it out yet.

I'll show you how to fake it though. I'm going to simplify this a bit. You'll need to apply the principle to your own code. The trick is kind of ugly. It requires that we call an Initialize routine each time we create a new child object

The Parent Class:

'Class Parent
Option Explicit

Private mName as String
Public Property Get Name() as String
    Name = mName()
End Property

Public Property Let Name(value As String)
    mName = value
End Property

The Child class

'Class Child
Option Explicit

Private mParent as Parent    

Public Property Get Parent() as Parent
    Set Parent = mParent
End Property

Public Property Let Name(Obj as Parent)
    Set mParent = Obj
End Property

Public Sub Initialize(Obj as Parent)
    Set Me.Parent = Obj
End Sub

Creating a Child object:

Sub CreateChild()
    Dim parentObject As New Parent
    ' create child object with parent property
    Dim childObject As New Child
    childObject.Initialize(parentObject)
End Sub