Implements WithEvents

[Sam Finch]

I'm trying to work out how to use the Implements keyword properly, And I can't Get it to work If i'm using Events.

Say I have a class clsInterface

Event MyEvent()



Public Property Get MyProperty As Long

End Property

Public Property Let MyProperty (New_MyProperty As Long)

End Property

Public Sub MyMethod()

End Sub

Now I want several Different classes (say cls1,cls2 and cls3) to Implement this interface so I can do something like this

Dim WithEvents objInstance As  clsInterface

Private Sub Form_Load

Select Case Fix(Rnd * 3)

    Case 0
        Set objInstance = New cls1

    Case 1
        Set objInstance = New cls2

    Case 2
        Set objInstance = New cls3

End Select

End Sub

And of coure some other code to make it do something useful

When I try to do this I always get an "Object Or Class does Not Support the set of Events" Error, no matter what events I try to put in cls1, cls2 and cls3.

Can anyone give me an example of a class that Implements clsInterface properly and Supports the Set of Events.

Thanks in Advance.

[S@NSIS]

Hi,
Using implements, your interface that you are implementing cannot have events.

From MSDN
Implements only implements an interface for methods and properties.

So...
You will have to put your events in each class yourself that implements your interface.

eg.

'Interface named Iinterface
Option Explicit

Public Function GetData() As String
'No code goes here as this is purely an interface
End Function

Public Sub LoadData()
'No code goes here as this is purely an interface
End Sub



'Class named clsData
Option Explicit

Implements Iinterface
Public Event DataChanged() 'put your event in this class

Private Function iinterface_GetData() As String
'Code goes here to get data
End Function

Private Sub iinterface_LoadData()
'Code goes here to load data
End Sub


'And then in your form:
Option Explicit

Dim WithEvents objObject As clsdata

Private Sub Form_Load()
   Set objObject = New clsdata
End Sub

Private Sub objObject_DataChanged()
   'Has its own event
End Sub

This probably hasn't helped in any way but hey..it might do!

Shaun

P.S. I am just getting to grips with this stuff so if anybody does have a solution...feel free to post it

[Sam Finch]

Not really what I wanted to hear, but thanks anyway, Unfortunatley I can't use your code in this example because I need to use several different class modules with the same Interface and raising vents from them, so I have to declare them all as a single type of object. (Which is where I thought the implements keyword would be really handy as I'm pretty sure that's what it was designed for.)


Does anyone else know a good way around this?

[S@NSIS]

Hi Sam,
I have been looking around (mainly in the new book I had delivered today!!) and you use the Implements keyword to keep your objects interfaces consistent but this definately only applies to properties and methods.

The original class that you use as the interface does not have any code in, it is only a template for others and as such cannot have events in it.

Therefore, for every class that you create that implements your interface you will have to define the events within them each time.

This is fine if you didn't want to declare them all as an interface object (in your case clsInterface), but you can't do this because an implemented interface simply does not support events and there is no way round this, sorry.

Shaun