The CBN_DBLCLK notification message is sent when the user double-clicks a string in the list box of a combo box. The control's parent window receives this notification message through a WM_COMMAND message.
wParam
Specifies the identifier of the combo box.
lParam
Specifies the handle of the combo box in the low-order word and the CBN_DBLCLK notification message in the high-order word.
This notification message can occur only for a combo box with the CBS_SIMPLE style. For a combo box with the CBS_DROPDOWN or CBS_DROPDOWNLIST style, a double-click cannot occur because a single click hides the list box.