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Wednesday, September 8, 2010

How to create custom collection in VBA tricks

This solution was taken from a forum entry I found on the web

You can, but the process is a bit more manual. If you export a .cls file from one of your VB6 proceedures and view it in a Notepad, you'll notice that some Attributes, not visible while editing your code, are added to the top of the routine(s).

The two properties in question will look something like this:
Property Get Item(Index As Variant) As Parameter
     Attribute Item.VB_UserMemId = 0
     Set Item = m_Collection.Item(Index)
End Property

Property Get NewEnum() As IUnknown
    Attribute NewEnum.VB_UserMemId = -4
    Attribute NewEnum.VB_MemberFlags = "40"
    Set NewEnum = Me.mCollection.[_NewEnum]
End Property

Now the above all looks "normal" except for the addition of the three "Attribute" Lines.

In the Item Property the line "Attribute Item.VB_UserMemId = 0" makes it the default property.

In the NewEnum, the "Attribute NewEnum.VB_UserMemId = -4" makes it the Default Enumeration Property (I'm sure you recognize the "-4" part.)

The Attribute NewEnum.VB_MemberFlags = "40" is to make the Enumerator a Hidden property, but, technically, this is not recognized in VBA, so it will be visible in IntelliSense, but I don't find that a big deal.

The solution is to (1) Make your Class, (2) SAVE, (3) Export the Class, (4) Remove the Class (steps 3 and 4 can be combined into one, as it asks you if you wish to "Export" when you right-click and choose "Remove") and then (5) Manually add the Attribute Lines as shown above, (6) Re-Import the edited Class.

(Btw, you can add the Attribute NewEnum.VB_MemberFlags = "40" line if you wish -- it won't hurt anything -- but it won't be recognized in VBA, it will just be quietly ignored. So there's no reason to bother doing this, really.)

As you know, editing the code thereafter has some propensity to lose these properties (even in VB6) and so this may have to be repeated occassionally. (A bit of a pain.)

The alternative is to create your class 100% within VB6 and then import it into your VBA Project.

Or, even better, make it in VB6, debugg it, get it running 100%, compile to DLL and then add this DLL to your references. This last concept is probably the most solid, but there could be deployment issues as your DLL now has to be correctly Registered on the Client machine. Not that this is a big problem, but it's not as easy as distributing a VBA Project...

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