CBN_DBLCLK
idComboBox = LOWORD(wParam);
hwndComboBox = (HWND)lParam;
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.
idComboBox
Value of low word of wParam. Specifies the combo-box ID.
hwndComboBox
Value of lParam. Specifies the combo-box window handle.
This message can only occur for a combo box with a list box that is always visible. For combo boxes with drop-down list boxes, a single click closes the list box and so a double-click cannot occur.
WM_COMMAND