Question

Please consider the following scenario:

Class Class1
 Function Func() as String
 End Function
End Class

Class Class2
 Function Func() as String
 End Function

 Function Func2() as String 
 End Function
End Class 

Class Class3

Function GetClassObject as Object
 If (certain condition meets)
   return new Class1();
 Else
  return new Class2();
 End If
End Function

Main()
Object obj1 = GetClassObject();
obj1.Func(); // Error: obj1.Func() is not defined:
End Main

End Class

Question: How to access obj1.Func() given the condition that for some reason I cannot inherit Class1 and Class2 from a common Interface class?

Thank you

Update:
One approach I used to address the problem and failed is as follows:

    Interface ICommon
     Function Func() as string
    End Interface

    Class Class3
    ...
        Main()

        Dim obj1 as ICommon = TryCast(GetClassObject(), ICommon); //Error: obj1 is "Nothing"
        obj1.Func()

or simply: 

TryCast(GetClassObject(), ICommon).Func() //Error: obj1 is Nothing

        End Main
    ...
    End Class

Answer 1

You can try this

Object obj1 = GetClassObject();

If TypeOf obj1 Is Class1 Then 
   DirectCast(obj1 , Class1).Func()
ElseIf TypeOf obj1 Is Class2 Then 
   DirectCast(obj1 , Class2).Func()
End If

Or You can also try

Dim c1 As Class1 = TryCast(obj1, Class1) 
IF Not c1 Is Nothing Then
    c1.Func()
Else
   Dim c2 As Class2 = TryCast(obj1, Class2) 
   IF Not c2 Is Nothing Then
      c2.Func()
   End If
End If

Or you can try With Reflection.

Dim result as String = obj1.GetType().GetMethod("Func").Invoke(obj1, null)