Binaryworld - Open the list portion of a ComboBox control ... [ VB -> Forms & Controls ]

To programmatically open and close the list portion of a ComboBox control, all you need is sending the CB_SHOWDROPDOWN message to the control. Here is a routine that encapsulate the SendMessage API function:

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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
Const CB_SHOWDROPDOWN = &H14F
Const CB_GETDROPPEDSTATE = &H157

' Show or hide the list portion of a combobox

Sub ComboBoxOpenList(cbo As ComboBox, Optional showIt As Boolean = True)
  SendMessage cbo.hwnd, CB_SHOWDROPDOWN, showIt, ByVal 0&
End Function

Retrieving the current visibility state of the list portion of a ComboBox can be done by sending a message, too. Here is a wrapper function that does it all:

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' Returns True if the list portion of a combobox is visible

Function ComboBoxIsListVisible(cbo As ComboBox) As Boolean
ComboBoxIsListVisible = SendMessage(cbo.hwnd, CB_GETDROPPEDSTATE, 0, _
ByVal 0&)
End Function