VB Forum / General / December 2004

One way of doing this is to have an Attach and Detach method of each class that allows it to store it's parent object, probably the
easiest way of doing this is you have multiple classes in your project is to use an interface which exposes the functionality:

'*** IParentTrack
Public Property Get ParentObj() As Object
End Property

Public Sub AttachParent(ByRef inParent As Object)
End Sub

Public Function DetachParent() As Boolean
End Function
'***

Then each class you need to know it's parent object can simply implement the interface:

'***
Implements IParentTrack

Dim m_ParentObj As Object

Private Property Get IParentTrack_ParentObj() As Object
   Set IParentTrack_ParentObj = m_ParentObj
End Property

Private Sub IParentTrack_AttachParent(ByRef inParent As Object)
   m_ParentObj = inParent
End Sub

Private Function IParentTrack_DetachParent() As Boolean
   IParentTrack_DetachParent = Not (m_ParentObj Is Nothing)
   m_ParentObj = Nothing
End Function
'***

You must remember to call DetachParent() on each before you want to destroy it though otherwise you're left with a circular
reference.  If you don't like this solution then you could store a 'soft pointer' to the parent by using the ObjPtr() function
instead:

'*** IParentTrack
Public Property Get ParentPtr() As Long
End Property

Public Sub AttachParent(ByRef inParent As Object)
End Sub

Public Function DetachParent() As Boolean
End Function
'***

'***
Implements IParentTrack

Dim m_ParentPtr As Long

Private Property Get IParentTrack_ParentPtr() As Long
   IParentTrack_ParentPtr = m_ParentPtr
End Property

Private Sub IParentTrack_AttachParent(ByRef inParent As Object)
   m_ParentObj = ObjPtr(inParent)
End Sub

Private Function IParentTrack_DetachParent() As Boolean
   IParentTrack_DetachParent = (m_ParentPtr <> 0)
   m_ParentObj = 0
End Function
'***

This doesn't quite give you the flexibility of the first solution, but doesn't create any circular references.  If you need to get
back to the parent object from the pointer then you can use this function:

'***
Private Declare Sub PutDWord Lib "MSVBVM60.dll" Alias _
   "PutMem4" (ByRef inDst As Any, ByVal inSrc As Long)

...

Private Function ResolveObjPtr(ByVal inPtr As Long) As Object
   Dim TempObj As Object

   If (inPtr) Then
       Call PutDWord(TempObj, inPtr)
       Set ResolveObjPtr = TempObj
       Call PutDWord(TempObj, 0&)
   End If
End Function
'***

If the parent object has already been released though, this will give you back an invalid object which will more thank likely kill
the IDE if you attempt to use it, so be careful when using it..
If you're in a position to use a class factory for your object creating then it's possible to add parent/child relationships
directly into it including communication between the parent and child classes for when either gets destroyed - Have a look at the
class factory and subject/observer design patterns if you want to know more on this approach.
Hope this helps,

   Mike

- Microsoft Visual Basic MVP -
E-Mail: EDais@mvps.org
WWW: Http://EDais.mvps.org/

On Thu, 30 Dec 2004 08:37:01 -0800, "=?Utf-8?B?QWwgTWVhZG93cw==?="
<AlMeadows@discussions.microsoft.com> wrote:

<snip>

A simple halfway house is to stick code in the Initialize and
Terminate Events of every Class, UC and Form

That code 'registers'/'unregisters' itself with a dinky utility in a
BAS module that maintains an Array of names (and I suggest pseudo
handles)

As a starter look at :

 Private Sub Command1_Click()
     Me.Print TypeName(Me)
 End Sub

Consider this :
    Private cmnHandle As Integer

    Private Sub Class_Initialize
           cmnHandle = DbgMod.RegObj( Me )
    End Sub

And in DbgMod.bas

    Public Function RegObj( Obj As Object ) As Integer
          Dim S As String
          S$ = TypeName( Obj )  
          RegObj = Local_StoreRefStr( S$ )
    End Function

On return the Object 'knows' its own 'Handle', so in the
Class_Terminate event you can tell DbgMod.bas to delete that reference
from the list it is holding

    Call DbgMod.UnRegObj( cmnHandle )

To get to the next stage of your Wish List you give each Class a
property or a Method that takes the Parent/Creator and appends that to
the interesting data in DbgMod.bas
- obviously via the Class

Something like :
    Call oMyObj.RegParent(  Me )  ' if Me is an Object

The nice thing is that at any point one can do a MsgBox (or similar)
of all living Objects - nice to see an inventory of Objects

In my case I have never bothered to record the ancestry, because as
soon as I find a little sucker that refuses to 'die on demand',  I
simply hunt it down, locate its life support machine, and ensure that
it gets switched off.