我无法将新元素添加到地图列表

Question

我正在尝试实现一个日历，在该日历中它从我的数据库中获取日期信息，之后它与首先找到的日期相符（我正在尝试假期），但是在示例中，我从table_calendar小部件中找到了它使用的地图列表我并没有从动态流行起来，我的想法是通过getCalendar（）方法向我的php服务器发出请求，它返回一个带有信息的json，到目前为止，我还不能将数据放在列表中_holidays如您在我的代码中看到的，有人可以帮助我吗？下面是我的完整代码：

//  Copyright (c) 2019 Aleksander Woźniak
//  Licensed under Apache License v2.0

import 'package:flutter/material.dart';
import 'package:intl/date_symbol_data_local.dart';
import 'package:table_calendar/table_calendar.dart';
import 'dart:convert';
import 'package:http/http.dart' as http;

// Holidays
Map<DateTime, List> _holidays = {
  DateTime(2019, 1, 1): ['New Year\'s Day'],
  DateTime(2019, 1, 6): ['Epiphany'],
  DateTime(2019, 2, 14): ['Valentine\'s Day'],
  DateTime(2019, 4, 21): ['Easter Sunday'],
  DateTime(2019, 4, 22): ['Easter Monday'],
};

void main() {
  initializeDateFormatting().then((_) => runApp(MyApp()));
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Calendar',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Calendar'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with TickerProviderStateMixin {
  Map<DateTime, List> _events;
  List _selectedEvents;
  AnimationController _animationController;
  CalendarController _calendarController;

  Future<Null> getCalendar() async {
    var url =
        "http://192.168.0.11/sistema/appCalendario.php?LgeOffID=1&LgeEmpID=115&bd=ac01";

    var client = new http.Client();
    try {
      final response = await client.get(url);
      final result = json.decode(response.body);

      setState(() {
        listholidays = result['Holidays'];

        /*
          listholidays - Array('FerDay','FerMounth','FerYear','Ferdesc')
        */
        for (int i = 0; i < listholidays.length; i++) {}
      });
    } finally {
      client.close();
    }
  }

  @override
  void initState() {
    super.initState();
    getCalendar();

    final _selectedDay = DateTime.now();

    _events = {
      /*_selectedDay.subtract(Duration(days: 30)): [
        'Event A0',
        'Event B0',
        'Event C0'
      ],
      _selectedDay.subtract(Duration(days: 27)): ['Event A1'],
      _selectedDay.subtract(Duration(days: 20)): [
        'Event A2',
        'Event B2',
        'Event C2',
        'Event D2'
      ],
      _selectedDay.subtract(Duration(days: 16)): ['Event A3', 'Event B3'],
      _selectedDay.subtract(Duration(days: 10)): [
        'Event A4',
        'Event B4',
        'Event C4'
      ],
      _selectedDay.subtract(Duration(days: 4)): [
        'Event A5',
        'Event B5',
        'Event C5'
      ],
      _selectedDay.subtract(Duration(days: 2)): ['Event A6', 'Event B6'],
      _selectedDay: ['Event A7', 'Event B7', 'Event C7', 'Event D7'],
      _selectedDay.add(Duration(days: 1)): [
        'Event A8',
        'Event B8',
        'Event C8',
        'Event D8'
      ],
      _selectedDay.add(Duration(days: 3)):
          Set.from(['Event A9', 'Event A9', 'Event B9']).toList(),
      _selectedDay.add(Duration(days: 7)): [
        'Event A10',
        'Event B10',
        'Event C10'
      ],
      _selectedDay.add(Duration(days: 11)): ['Event A11', 'Event B11'],
      _selectedDay.add(Duration(days: 17)): [
        'Event A12',
        'Event B12',
        'Event C12',
        'Event D12'
      ],
      _selectedDay.add(Duration(days: 22)): ['Event A13', 'Event B13'],
      _selectedDay.add(Duration(days: 26)): [
        'Event A14',
        'Event B14',
        'Event C14'
      ],*/
    };

    _selectedEvents = _events[_selectedDay] ?? [];

    _calendarController = CalendarController();

    _animationController = AnimationController(
      vsync: this,
      duration: const Duration(milliseconds: 400),
    );

    _animationController.forward();
  }

  @override
  void dispose() {
    _animationController.dispose();
    _calendarController.dispose();
    super.dispose();
  }

  void _onDaySelected(DateTime day, List events) {
    print('CALLBACK: _onDaySelected');
    setState(() {
      _selectedEvents = events;
    });
  }

  void _onVisibleDaysChanged(
      DateTime first, DateTime last, CalendarFormat format) {
    print('CALLBACK: _onVisibleDaysChanged');
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Column(
        mainAxisSize: MainAxisSize.max,
        children: <Widget>[
          // Switch out 2 lines below to play with TableCalendar's settings
          //-----------------------
          _buildTableCalendar(),
          // _buildTableCalendarWithBuilders(),
          /*const SizedBox(height: 8.0),
          _buildButtons(),*/
          const SizedBox(height: 8.0),
          Expanded(child: _buildEventList()),
        ],
      ),
    );
  }

  // Simple TableCalendar configuration (using Styles)
  Widget _buildTableCalendar() {
    return TableCalendar(
      locale: 'pt_BR',
      calendarController: _calendarController,
      events: _events,
      holidays: _holidays,
      startingDayOfWeek: StartingDayOfWeek.monday,
      calendarStyle: CalendarStyle(
        selectedColor: Colors.deepOrange[400],
        todayColor: Colors.deepOrange[200],
        markersColor: Colors.brown[700],
        outsideDaysVisible: false,
      ),
      headerStyle: HeaderStyle(
        formatButtonTextStyle:
            TextStyle().copyWith(color: Colors.white, fontSize: 15.0),
        formatButtonDecoration: BoxDecoration(
          color: Colors.deepOrange[400],
          borderRadius: BorderRadius.circular(16.0),
        ),
      ),
      onDaySelected: _onDaySelected,
      onVisibleDaysChanged: _onVisibleDaysChanged,
    );
  }

  // More advanced TableCalendar configuration (using Builders & Styles)
  Widget _buildTableCalendarWithBuilders() {
    return TableCalendar(
      locale: 'pt_BR',
      calendarController: _calendarController,
      events: _events,
      holidays: _holidays,
      initialCalendarFormat: CalendarFormat.month,
      formatAnimation: FormatAnimation.slide,
      startingDayOfWeek: StartingDayOfWeek.sunday,
      availableGestures: AvailableGestures.all,
      availableCalendarFormats: const {
        CalendarFormat.month: '',
        CalendarFormat.week: '',
      },
      calendarStyle: CalendarStyle(
        outsideDaysVisible: false,
        weekendStyle: TextStyle().copyWith(color: Colors.blue[800]),
        holidayStyle: TextStyle().copyWith(color: Colors.blue[800]),
      ),
      daysOfWeekStyle: DaysOfWeekStyle(
        weekendStyle: TextStyle().copyWith(color: Colors.blue[600]),
      ),
      headerStyle: HeaderStyle(
        centerHeaderTitle: true,
        formatButtonVisible: false,
      ),
      builders: CalendarBuilders(
        selectedDayBuilder: (context, date, _) {
          return FadeTransition(
            opacity: Tween(begin: 0.0, end: 1.0).animate(_animationController),
            child: Container(
              margin: const EdgeInsets.all(4.0),
              padding: const EdgeInsets.only(top: 5.0, left: 6.0),
              color: Colors.deepOrange[300],
              width: 100,
              height: 100,
              child: Text(
                '${date.day}',
                style: TextStyle().copyWith(fontSize: 16.0),
              ),
            ),
          );
        },
        todayDayBuilder: (context, date, _) {
          return Container(
            margin: const EdgeInsets.all(4.0),
            padding: const EdgeInsets.only(top: 5.0, left: 6.0),
            color: Colors.amber[400],
            width: 100,
            height: 100,
            child: Text(
              '${date.day}',
              style: TextStyle().copyWith(fontSize: 16.0),
            ),
          );
        },
        markersBuilder: (context, date, events, holidays) {
          final children = <Widget>[];

          if (events.isNotEmpty) {
            children.add(
              Positioned(
                right: 1,
                bottom: 1,
                child: _buildEventsMarker(date, events),
              ),
            );
          }

          if (holidays.isNotEmpty) {
            children.add(
              Positioned(
                right: -2,
                top: -2,
                child: _buildHolidaysMarker(),
              ),
            );
          }

          return children;
        },
      ),
      onDaySelected: (date, events) {
        _onDaySelected(date, events);
        _animationController.forward(from: 0.0);
      },
      onVisibleDaysChanged: _onVisibleDaysChanged,
    );
  }

  Widget _buildEventsMarker(DateTime date, List events) {
    return AnimatedContainer(
      duration: const Duration(milliseconds: 300),
      decoration: BoxDecoration(
        shape: BoxShape.rectangle,
        color: _calendarController.isSelected(date)
            ? Colors.brown[500]
            : _calendarController.isToday(date)
                ? Colors.brown[300]
                : Colors.blue[400],
      ),
      width: 16.0,
      height: 16.0,
      child: Center(
        child: Text(
          '${events.length}',
          style: TextStyle().copyWith(
            color: Colors.white,
            fontSize: 12.0,
          ),
        ),
      ),
    );
  }

  Widget _buildHolidaysMarker() {
    return Icon(
      Icons.add_box,
      size: 20.0,
      color: Colors.blueGrey[800],
    );
  }

  Widget _buildEventList() {
    return ListView(
      children: _selectedEvents
          .map((event) => Container(
                decoration: BoxDecoration(
                  border: Border.all(width: 0.8),
                  borderRadius: BorderRadius.circular(12.0),
                ),
                margin:
                    const EdgeInsets.symmetric(horizontal: 8.0, vertical: 4.0),
                child: ListTile(
                  title: Text(event.toString()),
                  onTap: () => print('$event tapped!'),
                ),
              ))
          .toList(),
    );
  }
}

var listholidays = [];

请注意，我的getCalendar（）方法会获取数据，并且在我扫描列表假日的位置，我想向_holidays添加新元素，这是我的列表地图

我尝试进行以下更改：

Future<Null> getCalendar() async {
    var url =
        "http://192.168.0.11/sistema/appCalendario.php?LgeOffID=1&LgeEmpID=115&bd=ac01";

    var client = new http.Client();
    try {
      final response = await client.get(url);
      final result = json.decode(response.body);

      setState(() {
        listholidays = result['holidays'];
        var data, aux = [];

        int day = 0, month = 0, year = 0;

        for (int i = 0; i < listholidays.length; i++) {
          aux.add(listholidays[i]['FerDesc']);
        }

        for (int i = 0; i < listholidays.length; i++) {
          year = int.parse(listholidays[i]['Feryear']);
          month = int.parse(listholidays[i]['Fermonth']);
          day = int.parse(listholidays[i]['Ferday']);
          data = new DateTime(year, month, day);
          _holidays.map(data: aux);
        }  
      });
    } finally {
      client.close();
    }
  }

但是出现以下错误： 预期需要1个自变量，但找到0个。 尝试添加其他必需的参数。dart（not_enough_required_arguments）

未定义命名参数“数据”。 尝试将名称更正为现有的命名参数，或使用此名称设置新参数。dart（undefined_named_pa​​rameter）

我不明白为什么我在示例中没有定义参数