Implementing my own interface in VBA - Error: Object module needs to implement 'x' for interface 'y'

Question

How do I implement my class ClsInterface, which has this code:

Public Function add(x As Integer, y As Integer) As Integer
End Function

in my class Class2, which has this code:

Implements ClsInterface

Public Function add(x As Integer, y As Integer) As Integer
add = x + y
End Function

My test code is

Public Sub test()
Dim obj As New Class2
MsgBox obj.add(5, 2)
End Sub

This always comes up with the following error:

Microsoft Visual Basic
Compile error:

Object module needs to implement 'add' for interface 'ClsInterface'
OK/Help

but there is no help on Microsoft help (when I press on Help button).

Any Ideas?

Alex K. · Accepted Answer · 2018-11-14 12:44:23Z

15

Your Class2 must look like:

Implements ClsInterface

Private Function ClsInterface_add(x As Integer, y As Integer) As Integer
    ClsInterface_add = x + y
End Function

Check out the drop-down boxes at the top of Class2's code window, you can see what base object you can refer to; Class or ClsInterface.

In your test code you want:

Dim obj As New ClsInterface

If you want to call across the interface.

I would also recommend naming interfaces in the form ISomeDescription and using Dim then Set rather than Dim As New.

answered Jul 3, 2010 at 11:33

Alex K.

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5 Comments

thank you, I followed your instructions it worked without any errors but the value is always 0 !!! while it should be 7, any idea?

In your Private Function ClsInterface_add... you need 'Return x + y' instead of 'add = x + y', otherwise the value of x+y never gets returned.

You need to return using; ClsInterface_add = x + y

this isn't using an interface it's replacing class2 with clsinterface as class

I just looked for over an hour how to auto-implement a damn COM Interface in VB6 until I found your hint with the Drop-down boxes. Thanks for that.