ItemData, ItemIdData

These two array properties let you associate a number with each item in a list or combo box.

Usage

oObject.ItemData( nIndex ) = nValue
nValue = oObject.ItemData( nIndex )
oObject.ItemIdData( nItemId ) = nValue
nValue = oObject.ItemIdData( nItemId )

There are two properties here where it seems one would do. Like List and ListItem, these are really just two names for the same array. The difference is in how you access them. ItemData keeps things in order by the item’s Index, while ItemIdData is ordered by the item’s unique ItemId. (See AddItem for an explanation of Index vs. ItemId.)

What does this dual-named array actually hold? By default, nothing. The elements get created as the list items are added, but there’s nothing there. You get to fill them up.

The docs say that these properties only work right up to 60 items. They’re partly right. In VFP 3, there were a number of problems with lists containing more than 60 items, but those got fixed in VFP 5. Of course, that’s the version where the limit was first documented. Oops. We’ve tested with lists containing up to 10,000 items (despite our feeling that that’s at least 9,000 more items than we think should be in any list box), and ItemData and ItemIdData had no problem keeping up.

At first glance, we thought these would be pretty cool. We could imagine sticking, say, employee names in the list and putting their IDs in ItemData/ItemIdData. But you can only put numbers in these, not other types. While that works if you’re using Integers for surrogate IDs, you can also just put the IDs into the list and not show them. And, in fact, if your list is based on an array or a table, all the data is available through the List and ListItem collections anyway.

We have come up with one case where ItemData/ItemIdData seems useful. Suppose you have an array or table and you want to put some (but not all) of the items in a list. You can use AddItem or AddListItem to put the items you want in the list and then use this array to hold the row number in the original array or the record number (or primary key) of the item. Then, when the user picks an item, you can look up the row or record number and get right back to the original data.

Of course, there are other ways to handle this situation, but we’ll never turn down a gift horse. Bottom line—we have yet to use these properties, other than for testing.

Example

* Fill a list with only those Employees that have a
* sales region listed. Set up ItemData to hold the
* recno() for each such employee.
SELECT Employee
SCAN
   IF NOT EMPTY(Sales_region)
      This.AddItem(Last_Name)
      This.ItemData[ This.NewIndex ] = RECNO()
   ENDIF
ENDSCAN

See Also

AddItem, ComboBox, List Property, ListBox, ListIndex, ListItemId, NewIndex, NewItemId