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Collection Classes

Posted on 1998-07-31
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Last Modified: 2013-11-25
I'm implementing a library of COM objects using ATL.  I need to expose numerous collections to the client.  My primary clients will be written in VB, so the ideal resulting syntax would be:
v= obj(index).value
o= obj(index).otherValue
Or
v= obj.item(index).value
o= obj.item(index).otherValue

I've seen these two variations in syntax used before, how do I implement them with ATL?  Please provide references and code examples.

Thanks.

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Question by:rayb
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endeavor earned 200 total points
ID: 1320038
Make sure you have the Item method specified as the default member (id(0)) of your collection class in your .idl file. For example:

interface IMyCollection : IDispatch
{
    [id(0), helpstring ("method Item")] HRESULT _stdcall Item([in] VARIANT * Index, [out, retval] VARIANT * pItem);

}

The key here is to specify id(0) for the member you want ot be the default.  Then you can use either:

v = myCollection.Item(Index)  

Or

v = myCollection(Index)

I have found it really helpful to use the OLE/COM Object Viewer to decompile other type libraries (such as Visual Basic for Applications).  If you want things to act the same as other objects just make sure your .idl specifications match.

-- George


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Author Comment

by:rayb
ID: 1320039
This works great, George.
Thanks.

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