如何将数据从函数内部传递到不同的类中

Question

作为Flutter的初学者，我正在尝试构建一个日历应用程序，我想在其中从Firestore数据库中提取特定日期的数据。现在有一个_onDaySelected函数，可在flutter控制台中从日历中打印选定的日期，例如“ flutter：2019-11-04”。我希望将此字符串传递给MessagesStream类，以便可以调用.document（'$ currentDay'）而不是像这样对日期进行硬编码：.document（'2019-11-04'）。我已包含以下代码。

有人知道该怎么做吗？任何帮助，将不胜感激！

class RoosterTest extends StatefulWidget {

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

class _RoosterTestState extends State<RoosterTest>
    with TickerProviderStateMixin {
  Map<DateTime, List> _events;
  List _selectedEvents;
  AnimationController _animationController;
  CalendarController _calendarController;
  final messageTextController = TextEditingController();

  String messageText;

  static final now = DateTime.now();
  static final formatter = DateFormat('yyyy-MM-dd');
  static final formatted = formatter.format(now);

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

    final _selectedDay = DateTime.now();
    _events = {};

    _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) {
    String currentDay = formatter.format(day).toString();
    print('$currentDay');
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        mainAxisSize: MainAxisSize.max,
        children: <Widget>[
          _buildTableCalendar(),
          const SizedBox(
            height: 8.0,
          ),
          MessagesStream(),
        ],
      ),
    );
  }

Widget _buildTableCalendar() {
    return TableCalendar(
      calendarController: _calendarController,
      events: _events,
      startingDayOfWeek: StartingDayOfWeek.monday,
      calendarStyle: CalendarStyle(
        selectedColor: Colors.red,
        todayColor: Colors.blue,
        markersColor: Colors.green,
        outsideDaysVisible: false,
        weekendStyle: TextStyle().copyWith(color: Colors.red),
      ),
      headerStyle: HeaderStyle(
        formatButtonTextStyle:
            TextStyle().copyWith(color: Colors.white, fontSize: 15.0),
        formatButtonDecoration: BoxDecoration(
          color: Colors.red,
          borderRadius: BorderRadius.circular(16.0),
        ),
      ),
      onDaySelected: _onDaySelected,
      onVisibleDaysChanged: _onVisibleDaysChanged,
    );
  }

class MessagesStream extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return StreamBuilder<QuerySnapshot>(
      stream: _firestore
          .collection('days')
          .document('2019-11-04')
          .collection('hours')
          .snapshots(),
      builder: (context, snapshot) {
        if (!snapshot.hasData)
          return CircularProgressIndicator(
            backgroundColor: Colors.lightBlueAccent,
          );

        return _buildList(context, snapshot.data.documents);
      },
    );
  }

Answer 1

您可以将_onDaySelected方法的结果存储在状态类的变量中：

class _RoosterTestState extends State<RoosterTest>
    with TickerProviderStateMixin {
    String stringOfSelectedDay='defaultValue';
[...]

[不要忘了第一次打开应用程序，您应该为stringOfSelectedDay提供默认值。尚未调用_onDaySelected时，您的MessagesStream应该返回什么？也许今天是日期？

因此，在方法上您可以像这样存储它：

void _onDaySelected(DateTime day, List events) {
    String currentDay = formatter.format(day).toString();
    setState(() { 
        stringOfSelectedDay = currentDay; 
    });
    print('$currentDay');
  }

您必须使用setState来使MessagesStream在日期改变后重建自身。

此后，必须使您的MessagesStream类具有最终变量，以使其基于该变量构建流，并为其赋予其值的构造函数：

class MessagesStream extends StatelessWidget {
  final String date;
  MessagesStream(this.date); //Constructor
  @override
  Widget build(BuildContext context) {
    return StreamBuilder<QuerySnapshot>(
      stream: _firestore
          .collection('days')
          .document(date) // Using the final variable here
          .collection('hours')
          .snapshots(),
      builder: (context, snapshot) {
        if (!snapshot.hasData)
          return CircularProgressIndicator(
            backgroundColor: Colors.lightBlueAccent,
          );

        return _buildList(context, snapshot.data.documents);
      },
    );
  }

因为您使用了setState，所以此小部件将反映_onDaySelected方法的不同调用。

最后，当您调用要构造的Widget时，相应地传递变量：

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        mainAxisSize: MainAxisSize.max,
        children: <Widget>[
          _buildTableCalendar(),
          const SizedBox(
            height: 8.0,
          ),
          MessagesStream(stringOfSelectedDay), //Using the new constructor you've made.
        ],
      ),
    );
  }