如何在 flutter/dart 中使用另一个类属性

Question

i have a calendar and i want to use its date property in another class i already tried to make object but that does not work here is what i tried for instantiate

var myCalender = MyCalendar();

and in the class i want to say something like

Text('$myCalendar.date');

and here is my calendar class

    class MyCalendar extends StatefulWidget {
      @override
      _MyCalendarState createState() => _MyCalendarState();
    }
    
    class _MyCalendarState extends State<MyCalendar> {
      static DateTime date = DateTime.now();
      TimeOfDay timeOfday = TimeOfDay.now();
    
      Future<Null> selectDate(BuildContext context) async {
        final DateTime picked = await showDatePicker(
   //show date picker Entrances i did not copy those to make the code shorter for you :)
        if (picked != null && picked != date) {
          print('date is ${date.toString()}');
        }
      }
    
      @override
      Widget build(BuildContext context) {
        return Container(
            child: FlatButton(
          onPressed: () {selectDate(context);},
          child: Text('calendar'),
          color: Colors.blue,
        ));
      }
    }

and here is my main.dart for global key

void main() {
  runApp(MyApp());
}
final key = GlobalKey<State<CustomCalendar>>();
class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: Container(child: Text('data'),),
    );
  }
}

Answer 1

You are actually trying to access a property of the state of MyCalendar rather than of MyCalendar itself. To expose the state you can refer to this answer how to access an object created in one stateful widget in another stateful widget in flutter and implement it like this for example:

final key = new GlobalKey<_MyCalendarState>();

void test(){
  print(key.currentState.date.toString());
}

class MyCalendar extends StatefulWidget {
  MyCalendar({Key key}) : super(key: key);

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

class _MyCalendarState extends State<MyCalendar> {
  DateTime date = DateTime.now();
  TimeOfDay timeOfday = TimeOfDay.now();

  Future<Null> selectDate(BuildContext context) async {
    final DateTime picked = await showDatePicker(
      //show date picker Entrances i did not copy those to make the code shorter for you :)
    if (picked != null && picked != date) {
      print('date is ${date.toString()}');
    }
  }

  @override
  Widget build(BuildContext context) {
    return Container(
        child: FlatButton(
          onPressed: () {selectDate(context);},
          child: Text('calendar'),
          color: Colors.blue,
        ));
  }
}

Note I've removed static in front of date as presumably you will want to change the date and static members are not accessible through currentState. If you don't need date to ever be anything other than DateTime.now() then you probably don't need to access the widget state and can just refer to DateTime.now() directly from the other widget.

Answer 2

class MyCalendar extends StatefulWidget {
 DateTime date = DateTime.now();
      @override
      _MyCalendarState createState() => _MyCalendarState();
    }

and in _MyCalendarState use widget.date