Question

I have a VB6 application with a search screen. On the search, I have 9 combo boxes. Some of the combo boxes only have a couple items, but some have a couple hundred items. It takes a long time (couple of seconds) to populate the data.

Each combo box is configured the same: Sorted = False, Style = 2 – Dropdown List

3 of the combo boxes have less that 20 items.
1 has 130 items.
4 have approximately 250 items
1 has almost 700 items.

I fill all nine combo boxes with similar code.

While Not RS.EOF

    cmbX.List(i) = RS("Description")
    cmbX.ItemData(i) = RS("Id")

    i = i + 1

    RS.MoveNext
Wend

I tried setting Visible = False but it had no effect on performance.

Is there another way to fill the combo box that will perform better than my existing method?

Answer 1

Here is something you can try. According to this post you can shave about 60% off your overhead by using a Windows API function to populate the combo box, instead of the usual AddItem method:

Private Const CB_ERR As Long = -1
Private Const CB_ADDSTRING As Long = &H143
Private Const CB_RESETCONTENT As Long = &H14B
Private Const CB_SETITEMDATA As Long = &H151

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

Public Sub AddItem(cmb As ComboBox, Text As Variant, Optional ItemData As Long)

   Dim l As Long
   Dim s As String

   If VarType(Text) = vbString Then
      s = Text
   Else
      s = Trim$(Str$(Text))
   End If

   l = SendMessage(cmb.hwnd, CB_ADDSTRING, 0&, ByVal s)
   If l <> CB_ERR Then
      SendMessage cmb.hwnd, CB_SETITEMDATA, l, ByVal ItemData
   End If

End Sub

Public Sub Clear(cmb As ComboBox)
   SendMessage cmb.hwnd, CB_RESETCONTENT, 0, 0&
End Sub

You might be able to shave a little more off by omitting the function call, and just calling the API function directly.