The ZGN_SORT notification message is sent when the user has double-clicked in a column header signaling a sort operation is about to take place. The parent window of the ZeeGrid control receives this notification message through the WM_COMMAND message.
ZGN_SORT
idZeeGrid = (int) LOWORD(wParam); //identifier of the ZeeGrid control
hwndZeeGrid = (HWND) lParam; //handle to the ZeeGrid control