Opc data Access Automation Specification

2.7

 

Collections 

OLE Automation collections are objects that support Count, Item, and a hidden property called _NewEnum. Any object 

that has these properties as part of the interface can be called a collection. In VB, a collection can be iterated using either 

of two idioms. 

The first method explicitly uses Count and Item to index the elements of the collection. 

 

14 

 

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OPC Data Access Automation Specification2.02 

For I = 1 To object.Count 

 

element = object.Item ( I ) 

 

 

‘or… 

element = object( I ) 

Next I 

 

The second method iterates through the available items using the hidden _NewEnum function: 

 

For Each element In object  

 

‘do something with element 

Next element 

 

The For Each method of iterating a collection is faster than the explicit Item method. 

Item can also be used to access a particular index, such as Item( 3 ). It doesn’t need to be used within a loop.