An Interface class is just an empty class template containing procedures to implement
class methods and properties as discussed in the subsections immediately following
"Implementing COM Components Through Class Modules" in this
chapter. You don't normally put any code or Private variable declarations in an
Interface class, only the blank procedures.
Therefore, the entire contents of an IVehicle Interface class might look like Listing 12.17.
LISTING 12.17
THIS IS ALL THE CODE REQUIRED TO SET UP THE IVEHICLE
INTERFACE CLASS
Option Explicit
Public Property Let Color(newval As Long)
End Property
Public Property Get Color() As Long
End Property
Public Property Get MaxSpeed() As Single
End Property
Public Property Let MaxSpeed(newval As Single)
End Property
Public Function Travel(xStart, yStart, xEnd, yEnd)
As Single
End Function
Notice that the IVehicle Interface provides
two properties (Color and MaxSpeed) and one method
(Travel).
You specify the type of each property and the number and type of the parameters
that the method receives as well as its return value. You specify absolutely no
behavior beyond this, however. The way that these members will function depends
completely on the programmer who uses this Interface in other classes.
