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Tip of the Day
Language: Visual Basic
Expertise: Beginner
Jun 15, 1999

Working With Collections

When working with collections, use an error handler to easily determine if a given key exists in the collection. If you try to access an item from a collection where the key doesn't exist, you'll get an error. Likewise, if you try to add an item that exists, you'll also get an error. This example shows an error handler for adding an item to a collection. To trap for errors where an item exists, trap error code 457:

 
Private Function BuildCustCol(CustList As ListBox) As _
	Collection
	On Error GoTo ProcError
	Dim colCust As Collection
	Dim lngCustCnt As Long
	Dim J As Long

	Set colCust = New Collection
	For J = 0 To CustList.ListCount - 1
		lngCustCnt = colCust(CStr(CustList.List(J))) + 1
		colCust.Remove (CStr(CustList.List(J)))
		colCust.Add Item:=lngCustCnt, _
			Key:=CStr(CustList.List(J))
	Next J
	Set BuildCustCol = colCust
	Set colCust = Nothing
	Exit Function

ProcError:
	Select Case Err
		Case 5 'collection item doesn't exist, so add it
			colCust.Add Item:=0, _
				Key:=CStr(CustList.List(J))
			Resume
		Case Else
		'untrapped error
	End Select

End Function
Joe Karbowski
 
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