Binaryworld - DuplicateListBox - Fast copy of the contents of a ListBox control ... [ VB -> Forms & Controls ]

Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal _
  hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, _
  lParam As Any) As Long
Private Declare Function LockWindowUpdate Lib "user32" (ByVal hwndLock As Long) _
  As Long

Const LB_RESETCONTENT = &H184
Const LB_GETCOUNT = &H18B
Const LB_GETTEXT = &H189
Const LB_ADDSTRING = &H180
Const LB_GETITEMDATA = &H199
Const LB_SETITEMDATA = &H19A

' Duplicate the contents of a ListBox control to another ListBox control
'
' Pass False to the last argument to append contents
' (the target control isn't cleared before adding elements)
'
' uses API functions for the fastest code

Sub DuplicateListBox(Source As ListBox, Target As ListBox, _
  Optional AppendMode As Boolean)
  Dim index As Long
  Dim itmData As Long
  Dim numItems As Long
  Dim sItemText As String

  ' prepare the receiving buffer
  sItemText = Space$(512)

  ' temporarily prevent updating
  LockWindowUpdate Target.hWnd

  ' reset target contents, if not in append mode
  If Not AppendMode Then
    SendMessage Target.hWnd, LB_RESETCONTENT, 0, ByVal 0&
  End If

  ' get the number of items in the source list
  numItems = SendMessage(Source.hWnd, LB_GETCOUNT, 0&, ByVal 0&)

  For index = 0 To numItems - 1
    ' get the item text
    SendMessage Source.hWnd, LB_GETTEXT, index, ByVal sItemText
    ' get the item data
    itmData = SendMessage(Source.hWnd, LB_GETITEMDATA, index, ByVal 0&)
    ' add the item text to the target list
    SendMessage Target.hWnd, LB_ADDSTRING, 0&, ByVal sItemText
    ' add the item data to the target list
    SendMessage Target.hWnd, LB_SETITEMDATA, index, ByVal itmData
  Next

  ' allow redrawing
  LockWindowUpdate 0

End Sub