如何将数据从子状态小部件传递到 Flutter 中的父小部件

Question

I have a Stateful widget 'DayPicker' in my flutter application. Code for the same is:

class DayPicker extends StatefulWidget {
  @override
  _DayPickerState createState() =>
      _DayPickerState();
}

class _DayPickerState extends State<DayPicker> {
  final values2 = List.filled(7, false);
  @override
  Widget build(BuildContext context) {
    var ht = MediaQuery.of(context).size.height;
    return Column(
      mainAxisSize: MainAxisSize.min,
      children: <Widget>[
        SizedBox(
          height: ht / 40,
        ),
        Text(
          'Selected Day(s): ${valuesToEnglishDays(values2, true)}',
          style: TextStyle(fontSize: ht / 40, fontStyle: FontStyle.italic),
        ),
        WeekdaySelector(
          onChanged: (v) {
            setState(() {
              values2[v % 7] = !values2[v % 7];
            });
          },
          values: values2,
          selectedFillColor: Colors.amber,
          selectedColor: Colors.black,
          selectedShape: RoundedRectangleBorder(
            borderRadius: BorderRadius.circular(5),
          ),
          shape: RoundedRectangleBorder(
            side: BorderSide(color: Colors.red.withOpacity(0.5)),
            borderRadius: BorderRadius.circular(25),
          ),
        ),
      ],
    );
  }
}

This widget is used to select the days of week as shown here:

I want the list of days to be passed into my Parent widget ie the widget using DayPicker(), so that I can store this list to Firebase Firestore. How can I do this? In case of Stateless widget there is a method to pass data from child to parent using callback but I wonder how to pass data in this case.

Answer 1

You can also use callback to handle in this case. You need to use it like widget.callback(value) where it is changing data on child. Run the bellow snippet and do a check yourself.

class AppX extends StatefulWidget {
  final String province;
  const AppX({
    Key? key,
    required this.province,
  }) : super(key: key);

  @override
  State<AppX> createState() => _AppXState();
}

class _AppXState extends State<AppX> {
  double? sliderValue;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        children: [
          Text("${sliderValue ?? 0}"), //handling null using defaul value
          Child(
            callback: (p0) {
              setState(() {
                sliderValue = p0;
              });
            },
          )
        ],
      ),
    );
  }
}

class Child extends StatefulWidget {
  const Child({
    Key? key,
    required this.callback,
  }) : super(key: key);

  final Function(double) callback;

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

class _ChildState extends State<Child> {
  double _sliderValue = 0;

  @override
  Widget build(BuildContext context) {
    return Slider(
      value: _sliderValue,
      onChanged: (value) {
        widget.callback(value);
        setState(() {
          _sliderValue = value;
        });
      },
    );
  }
}