Hi,
I have a simple code made of class interface, class and module to test it:
in my ClsInterface:
[vba]
Public Sub shape()
End Sub
[/vba]
class2:
[vba]
Implements ClsInterface
Private Sub ClsInterface_shape()
MsgBox ("test run")
End Sub
[/vba]
code to test it:
[vba]
Public Sub test()
Dim obj As New ClsInterface
obj.shape
End Sub
[/vba]
why cant i see the message box?
Without testing it, I think that obj.shape call the empty Public Sub shape()
Put your Msgbox in THAT sub and see if it works for you
Also, I think that 'Impliments' is a VB keyword, not a VBA keyword.
Paul
The class interface is abstract, all the coding is in the class that implements it.Originally Posted by Paul_Hossler
Yes. I never used it; I just take the default interface from a class. Learned somethingThe class interface is abstract, all the coding is in the class that implements it.
Make ClsInterface_shape Public and see if it works: From online Help
PaulWhen a Visual Basic class implements an interface, the Visual Basic class provides its own versions of all the Public procedures specified in the type library of the Interface. In
Paul, I've been curious about the use of Impliments for a while.
Do you have a link to the file your quote came from?
That was from the Excel 2010 online help.
I had never used / heard of 'Implements' until now.
I rarely use Classes in VBA, and when I do they're pretty basic
Paul
still doesnt work.
Module 1
[vba]
Public Sub test()
Dim obj As New clsInterface
obj.shape
End Sub
[/vba]
clsInterface
[vba]
Public Sub shape()
MsgBox ("test run")
End Sub
[/vba]
class2
[vba]
Implements clsInterface
Public Sub ClsInterface_shape()
End Sub
[/vba]
Been a learning experience, but unless I'm misunderstanding something (VERY possilble), it seems to work for me
Paul
Thanks for the file.
Don't say that until you're sure it worksThanks for the file.
Paul
Class2 is unnecessary now, and the code treats the interface like a normal class.
plus the class interface should be abstract, no code, all the coding is in the classes that implements the interface. instead of only 1 class you can add many more that everyone share the interface propeties/methods but still
each one of the classes can behave differently(polymorphism).
Yes, that part I can follow, but I can't even get the Implements on-line help example to work.
But it's a rainy Saturday here, and there's nothing interesting on TV, so this is more fun
Paul
I think that defining an abstract interface just allow objects that Impliments that interface to be assigned to variables of that
You do sort of get polymorphism, but not perfectly
clsInterface:
[vba]
Option Explicit
Public Sub shape()
'
End Sub
[/vba]
Class2:
[vba]
Implements clsInterface
Public Sub ClsInterface_shape()
MsgBox ("test run from Class2")
End Sub
[/vba]
and a Class3 that Implements the same interface as Class3 but has different processing in the shape()
[vba]
Implements clsInterface
Public Sub ClsInterface_shape()
MsgBox ("test run from Class3")
End Sub
[/vba]
The main sub
[vba]
Public Sub test()
Dim obj As New clsInterface
Dim obj2 As New Class2
Dim obj3 As New Class3
Set obj = obj2
obj.shape
Set obj = obj3
obj.shape
End Sub
[/vba]
It would seem to me (and you pointed it out) that in this example that you really don't need the complexity. The examples I saw used a library and books and a Collection. That would seem to me where polymorphism would be helpful. So thanks for an interesting Saturday afternoon. Much more fun than painting the bedroom.
If you're interested, I attached the library example that I was playing with.
I'm open to any and all suggestions
Paul
I'll keep looking for answers and let you know if i find one.
Thanks, I'd be interested
Even if it wasn't helpful,I learned a lot
Paul
Last edited by Paul_Hossler; 03-25-2012 at 07:09 AM.
What is the outstanding issue? It seems to me that Paul has already answered your question - your original calling sub should have been:
Your version was calling the interface class, not one of its implementations.Public Sub test() Dim obj As ClsInterface Set obj = New Class2 obj.shape End Sub
Be as you wish to seem
It would seem to me that Implements is VBA's way of trying to do OOP polymorphism (as the OP pointed out)
In my really simple example:
clsLibraryItem class defines the abstract interface, which clsFiction and clsHistory Implements
Since the interface 'looks' the same between clsFiction and clsHistory, I can assign either to an object of clsLibraryItem, and the polymorphic (if that's a word) method for the appropriate type of object gets called
[vba]
Sub test()
Dim i As Long
Dim MyLibrary(1 To 4) As clsLibraryItem
Dim FictionBook As New clsFiction
Dim HistoryBook As New clsHistory
Set MyLibrary(1) = New clsFiction
Set MyLibrary(2) = New clsFiction
Set MyLibrary(3) = New clsHistory
Set MyLibrary(4) = New clsHistory
MyLibrary(1).BookName = "Harry Potter (Fiction)"
MyLibrary(2).BookName = "War of the Worlds (Fiction)"
MyLibrary(3).BookName = "Civil War (History)"
MyLibrary(4).BookName = "Sparta (History)"
For i = 1 To 4
Call MyLibrary(i).LoanTimeMsg
Next i
End Sub
[/vba]
FWIW, this is pretty heavy stuff for me I'm sure there's lots more better ways that it could be done. But sure has been interesting, I'd like to see if the pros have additional examples
Paul
(Hit the wrong key)
(again)
Basically yes, but the point is that no function code goes in the Interface class, so whilst you declare the variable as implementing that interface, you actually create a variable using the implementing class.
Be as you wish to seem
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