Remove all items from the ListBox and edit control of a ComboBox
#include <GuiComboBox.au3>
_GUICtrlComboBox_ResetContent ( $hWnd )
| $hWnd | Control ID/Handle to the control | 
_GUICtrlComboBox_AddString, _GUICtrlComboBox_DeleteString
#include <GuiComboBox.au3>
#include <GUIConstantsEx.au3>
#include <WindowsStylesConstants.au3>
Example()
Func Example()
    Local $idCombo
    ; Create GUI
    GUICreate("ComboBox Reset Content", 400, 296)
    $idCombo = GUICtrlCreateCombo("", 2, 2, 396, 296, BitOR($CBS_SIMPLE, $CBS_DISABLENOSCROLL, $WS_VSCROLL))
    GUISetState(@SW_SHOW)
    ; Set Edit Text
    _GUICtrlComboBox_SetEditText($idCombo, "Edit Text")
    ; Add files
    _GUICtrlComboBox_BeginUpdate($idCombo)
    _GUICtrlComboBox_AddDir($idCombo, @WindowsDir & "\*.exe")
    _GUICtrlComboBox_EndUpdate($idCombo)
    Sleep(500)
    ; Reset content
    _GUICtrlComboBox_ResetContent($idCombo)
    ; Loop until the user exits.
    Do
    Until GUIGetMsg() = $GUI_EVENT_CLOSE
    GUIDelete()
EndFunc   ;==>Example