I am creating an object that implements quite a few interfaces. My problem is that there are a couple of variables that all the interfaces need access to. I know that I could put these variables in a module or shared class, but that is generally a sign of poor OOP design.

Is there any way that I could implement this without using global variables?

Here is a sample of the layout of the object. In the sample the Interfaces need to be able to get what the CurrentIndex is, but I don't want them to be able to change it at all. It should only be writeable from MainObject.

VB Code:
  1. Public Interface MainObject

  2. ReadOnly Property CurrentIndex as Integer

  3. ReadOnly Property If1 as Interface1

  4. ReadOnly Property If2 as Interface2

  5. ReadOnly Property If3 as Interface3

  6.  
  7. Function SetCurrentIndex(index as Integer)

  8.  
  9. End Interface

  10.  
  11. Public Interface Interface1

  12.     ReadOnly Property P1 as Something

  13.     ReadOnly Property P2 as Something

  14.     ReadOnly Property P3 as Something

  15.     ReadOnly Property P4 as Something

  16.  
  17.     Function F1(ST as Something) As Something

  18.     Function F3(ST as Something) As Something

  19.     Function F2(ST as Something) As Something

  20. End Interface

  21.  
  22. Public Interface Interface2

  23.     ReadOnly Property P1 as Something

  24.     ReadOnly Property P2 as Something

  25.     ReadOnly Property P3 as Something

  26.     ReadOnly Property P4 as Something

  27.  
  28.     Function F1(ST as Something) As Something

  29.     Function F3(ST as Something) As Something

  30.     Function F2(ST as Something) As Something

  31. End Interface

  32.  
  33. Public Interface Interface3

  34.     ReadOnly Property P1 as Something

  35.     ReadOnly Property P2 as Something

  36.     ReadOnly Property P3 as Something

  37.     ReadOnly Property P4 as Something

  38.  
  39.     Function F1(ST as Something) As Something

  40.     Function F3(ST as Something) As Something

  41.     Function F2(ST as Something) As Something

  42. End Interface