An application sends a ZGM_SORTSECONDARY message in response to the ZGN_SORT notification. This allows the application to programmatically determine the secondary sort column based on the column that the sort operation was requested on by the user double-clicking the column header.
ZGM_SORTSECONDARY wParam = (WPARAM)(int) iSecondarySortCol; //Secondary sort column lParam = 0; //not used; must be zero
This message does not return a value.
This message is primarily used when processing a ZGN_SORT notification message. By determining which column is being sorted, the application can vary the secondary sort column.