Dealing with List Flutter

List<History> dataFromLocal;

  List<Calc> calc = <Calc>[
    const Calc(calculation: '1x222', result: '222'),
    const Calc(calculation: '1x222', result: '222'),
    const Calc(calculation: '1x222', result: '222'),
    const Calc(calculation: '1x222', result: '222'),
  ];

  List<Calc> calc2 = <Calc>[
    const Calc(calculation: '2x222', result: '444'),
    const Calc(calculation: '2x222', result: '444'),
    const Calc(calculation: '2x222', result: '444'),
    const Calc(calculation: '2x222', result: '444'),
  ];

  List<Calc> calc3 = <Calc>[
    const Calc(calculation: '3x222', result: '666'),
    const Calc(calculation: '3x222', result: '666'),
    const Calc(calculation: '3x222', result: '666'),
    const Calc(calculation: '3x222', result: '666'),
  ];

  /*
  List<History> history = <History>[
    const History(date: '16 Maret', list: ),
  ];

  */

  History addHistory(String _date, List<Calc> _listcalc) {
    History todayHistory = new History(
      date: _date,
      listcalc: _listcalc
    );

    return todayHistory;
  }

  Map generateItems(calc, res) {
    Map<String, String> items = {'calculation': calc, 'result': res};

    return items;
  }



  List<Map> addToHistory(String calc, String res) {
    List<Map> theList = <Map>[
      generateItems(calc, res),
    ];
  }

  String now = new DateTime.now().toString();

  /*
  List<History> makeAHistory(String now, List<Calc> theListCalc) {
    List<History> theHistory = <History>[
      const History(
        date: now,
        listcalc: theListCalc,
      )
    ];
  }

  Map theMap = generateItems('2x222', '444');
  List<Map> historyaday = generateItems('2x222', '444');

  List<History> theHistory = <History>[
    const History(
      date: now,

    )
  ];
  */

//print(generateItems(theKey, theVal));

    //List<Map> listOfCalc;
    //listOfCalc.add(generateItems('2x33', '66'));

    History date16 = addHistory('Maret 16', calc);
    History date17 = addHistory('Maret 17', calc);
    History date18 = addHistory('Maret 18', calc);

    dataFromLocal = <History>[
      date16,
      date17,
      date18
    ];