REALbasic: Sharing common code between disparate subclasses

Question

I have two separate classes (A = a subclass of BevelButtom, B = a subclass of PushButton). Both A and B implement a number of identical methods in exactly the same way. Since both subclasses' superclasses are different and since RB doesn't support multiple inheritance, all I can do to tie these methods together is define a class interface, have both subclasses implement the interface, then copy/paste the method bodies in each subclass.

That offends my sensibilities. Is there a way in RB to extract this common logic elsewhere?

Thanks!

Answer 1

Using an interface seems like the right approach, but rather than copying the method bodies to each subclass, I think it makes more sense to create a new class (say CommonButtonStuff) with the common code. Then you can call it in the implemented methods:

CommonButtonInterface
  Sub Method1

Class CommonButtonHandler
  Sub DoMethod1
    MsgBox("Do it!")
  End Sub

Class A Inherits From PushButton, Implements CommonButtonInterface
  Private Property mCommonStuff As CommonButtonHandler

  Sub Constructor
    mCommonStuff = New CommonButtonHandler
  End Sub

  Sub Method1
    mCommonStuff.DoMethod1
  End Sub

Class B Inherits From BevelButton, Implements CommonButtonInterface
  Private Property mCommonStuff As CommonButtonHandler

  Sub Constructor
    mCommonStuff = New CommonButtonHandler
  End Sub

  Sub Method1
    mCommonStuff.DoMethod1
  End Sub

Answer 2

Use the Extends syntax from a module method to extend the class interface. You still need to use a class interface, but this way all the common code can be placed in the module instead of being duplicated across multiple classes.

Interface FooInterface
  Sub Foo()
End Interface

Class Foo
Implements FooInterface
  Sub Foo()
    MsgBox("Foo!")
  End Sub
End Class

Class Bar
Implements FooInterface
  Sub Foo()
    MsgBox("Bar!")
  End Sub
End Class

Module FooExtensions
  Sub Foobar(Extends FooImplementor As FooInterface)
    MsgBox("Foobar!")
  End Sub
End Module

The above FooBar method would be called like a class method of any class that implements the FooInterface class interface:

Dim myfoo As FooInterface = New Bar
myfoo.Foobar()

Note that extension methods don't count when the compiler is deciding whether a given class satisfies an interface.

This may not be workable, however, since the extension methods will only have access to the Interface rather than the actual class.

Alternatively, you could extend the RectControl class, though that would include all desktop controls, not just the PushButton and BevelButton.

A third option might be to use the BevelButton class exclusively.