Tips 2

Implement a For Each...Next Statement against a Collection Class

Most of the time, we take for granted the For Each...Next loop, which iterates the members of an array or a collection. It's the fastest, most efficient method of visiting all the members of the collection or array, and we could care less that, as it enumerates the collection, the unseen code is actually generating new references to members of the collection with each iteration of the loop. However, as the provider of a collection class, it is up to you to provide an interface that the For Each...Next statement can work with.

This may sound a little daunting, but you'll be pleasantly surprised how easy it is to implement a property that enumerates members of the collection within your class. First of all, you must create a Property Get procedure called NewEnum with the type of IUnknown. Its syntax is always the same:

Public Property Get NewEnum() As IUnknown
Set NewEnum = mCol.[_NewEnum]
End Property

where mCol is the name of your private collection object variable.

Second, set the Procedure ID for this Property Get procedure to -4. To do this, select the Procedure Attributes option from the Tools menu, then click the Advanced button on the Procedure Attributes dialog. Enter a Procedure ID of -4. You should also check the "Hide this member" option to prevent the property from appearing in the IntelliSense drop down.