The following code snippet adds 5000 items (both strings and items data) into a ComboBox.
It does it in 2 ways: with the standard AddItem method and ItemData property that Visual Basic provides, and by using Win32 API.
As you'll see, adding ComboBox items with Win32 API is much faster than doing it with standard VB way...

'Example for adding items into combo by using Win32 API. ' 'Written by Nir Sofer 'Web site: http://nirsoft.mirrorz.com 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 Const CB_ADDSTRING = &H143 Private Const CB_SETITEMDATA = &H151 Private Sub cmdComboAPI_Click() Dim strItemText As String Dim lngIndex As Long Dim dblTimer As Double Dim lngAddIndex As Long cmbTest.Clear dblTimer = Timer 'Adding items strings and items data with Win32 API For lngIndex = 1 To 5000 strItemText = "item number " & CStr(lngIndex) 'Add the new string to the ComboBox. lngAddIndex = SendMessage(cmbTest.hWnd, CB_ADDSTRING, 0, ByVal strItemText) 'Set the item data of the new item. SendMessage cmbTest.hWnd, CB_SETITEMDATA, lngAddIndex, ByVal lngIndex Next MsgBox Format(Timer - dblTimer, "0.000") & " seconds" End Sub Private Sub cmdComboVB_Click() Dim strItemText As String Dim lngIndex As Long Dim dblTimer As Double cmbTest.Clear dblTimer = Timer 'Adding items strings and items data with standard AddItem method. For lngIndex = 1 To 5000 strItemText = "item number " & CStr(lngIndex) cmbTest.AddItem strItemText cmbTest.ItemData(cmbTest.NewIndex) = lngIndex Next MsgBox Format(Timer - dblTimer, "0.000") & " seconds" End Sub

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