I have declared following variable:
data o type ref to I_OI_SPREADSHEET.
How to instantiate it?
I_OI_SPREADSHEET is an interface and you can't instantiate interfaces.
You can only create an instance of a class that implements this interface and assign this instance to your variable. Or you ask another class for an instance, e.g.:
CL_GUI_ALV_GRID_BASE->CREATE_VIEW_OI ... CALL METHOD m_oi_proxy->get_spreadsheet_interface IMPORTING sheet_interface = m_oi_spreadsheet. ...