VB Forum / COM / September 2005

I should add... this can come in handy once in a while. For one thing, it
allows you to keep track of the number of instances. If you wanted to limit
the number to exactly 2 (or whatever), you could raise an error in the
Initialize event, which would prevent it from being instantiated. A lot of
other uses too. This was the first that popped into my head.
'============UserControl code
Option Explicit

Private Sub UserControl_Initialize()
  glNumberOfInstances = glNumberOfInstances + 1
  If glNumberOfInstances > 2 Then
     glNumberOfInstances = glNumberOfInstances - 1
     Err.Raise 429 'use a more appropriate error
  End If
  Debug.Print glNumberOfInstances
End Sub

Private Sub UserControl_Terminate()
  glNumberOfInstances = glNumberOfInstances - 1
  Debug.Print glNumberOfInstances
End Sub

Public Property Get NumberOfInstances() As Long
  NumberOfInstances = glNumberOfInstances
End Property
'============Module code
Option Explicit

Public glNumberOfInstances As Long
'============

No, that doesn't work across processes.
Even in VB-Threads the Public Members of VBs "*.bas-Modules" are running
inside their own apartment and cannot be shared - the whole thing is working
only over multiple instances in the *same* thread.

Olaf