Determine when a ComboBox's area is being closed

' REQUIRES THE MSGHOOK.DLL COMPONENT

Const WM_COMMAND = &H111
Const CBN_DROPDOWN = 7
Const CBN_CLOSEUP = 8

Dim WithEvents FormHook As MsgHook

Private Sub Form_Load()
    ' subclass the form with events
    Set FormHook = New MsgHook
    ' you should pass the hWnd of the combobox container
    FormHook.StartSubclass Me.hWnd
End Sub

Private Sub FormHook_AfterMessage(ByVal uMsg As Long, ByVal wParam As Long, _
    ByVal lParam As Long, retValue As Long)
    Dim Ctrl As Control
    Dim ctrlIndex As Long
    Dim cmdCode As Long
    
    If uMsg = WM_COMMAND Then
        ' on entry, lParam holds the hWnd of the control
        ' the high word of wParam contains the actual command code
        ' the low word of wParam contains the control ID
        ' ( this is the index of the control in the Controls collection + 1)
        ctrlIndex = (wParam And &HFFFF&) - 1
        Set Ctrl = Me.Controls(ctrlIndex)
        cmdCode = (wParam And &HFFFF0000) \ &H10000

        If Not TypeOf Ctrl Is ComboBox Then
            ' this should never happen
        ElseIf cmdCode = CBN_DROPDOWN Then
            ' the list area is being opened
            Debug.Print Ctrl.Name & " is being opened"
        ElseIf cmdCode = CBN_CLOSEUP Then
            ' the list area is being closed
            Debug.Print Ctrl.Name & " is being closed"
        End If
    End If
End Sub