An easy and safe technique for preventing circular references  in Visual Basic 6

Avoiding a circular reference in VB6 (VB 6, classic VB, VB classic)

How to prevent a circular reference in VB6

How to avoid a circular reference in VB6

by VT Software

Summary

A weak reference (or uncounted reference) to an object is one that does not prevent the object from terminating.

Imagine for a moment that Microsoft had designed VB6 with a built-in WeakReference type, that every object had a built-in property that returned a weak reference to the object, and that a weak reference could easily be converted back to a normal reference. Avoiding circular references would then be very easy. You would just store weak references to parent objects in the child objects.

Imagine no more! With a few lines of code you can customise any VB6 project to achieve all this. Here's how:

Step by step

1    Download WeakReference.cls and add it to your project, or compile it in a DLL used by all your projects.

2    Add a WeakReference property to your root class by copying and pasting the following code into your root class module.  It does not need any modification:

'Weak reference to this object (module level variable declaration)
Private mWeakReference As WeakReference

Friend Property Get WeakReference() As WeakReference
    'Return a weak reference to this object
    Set WeakReference = mWeakReference
End Property

Private Sub Class_Initialize()
    'Create a weak reference to this object
    Set mWeakReference = New WeakReference
    mWeakReference.Initialize Me
End Sub

Private Sub Class_Terminate()
    'Reset the weak reference. If this method is not called and this
    'object is accessed after it has terminated, VB will crash.
    mWeakReference.Destroy
End Sub

3    Add a Parent property to dependent classes by copying and pasting the following code into any dependent class module (where Root is the name of your root class):

'Weak reference to root object (module level variable declaration)
Private mwrRoot As WeakReference

Public Property Get Parent() As Root
    'Convert weak reference back to a normal reference
    Set Parent = mwrRoot.Target
End Property

Friend Property Set Parent(NewValue As Root)
    'Store a weak reference to the root object
    Set mwrRoot = NewValue.WeakReference
End Property

We would be pleased to find out how you get on using this code. Please send an email.

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