Returning data from a Stateful Widget in Flutter

Question

I have previously posted about this problem I am still facing Which is to return data from a Stateful widget back to a Stateless Widget

The Widget I am using is DateTimePickerFormField widget and I am using it as a child in a stateful widget

So I have looked at https://flutter.io/docs/cookbook/navigation/returning-data#complete-example

For returning data from a widget. However, the widget that is returning the data is a stateless widget ...Which in my case isn't

So The code goes as follows

Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Add a Reminder'),

      ),
      body:
      new Container(
        padding: new EdgeInsets.all(20.0),
        child: new Form(
            child: new ListView(
              children: <Widget>[

            new TextFormField(
            keyboardType: TextInputType.text,
              // Use email input type for emails.
              decoration: new InputDecoration(
                hintText: 'Title of reminder',
              ),

            ),
            dateAndTimeWidget(context),
            RaisedButton(
            child: Text('Save'),
        onPressed: () {
          Navigator.pop(context);
        },
      )
      ],
    ),)
    ,
    )
    ,
    );

  }

That Widget is calling the method: dateAndTimeWidget, Which is supposed to return the dateTime stateful widget and save the outcoming data in a variable :

 dateAndTimeWidget(BuildContext context) async {
    final result = await Navigator.push(
      context,
      MaterialPageRoute(builder: (context)=> dateTime()),
    );

}

Then This is the dateTime Statful widget

class dateTime extends StatefulWidget{
    @override
  dateTimeState createState() => dateTimeState();

}
class dateTimeState extends State<dateTime>{

  static DateTime dateT;

  InputType inputType = InputType.both;

  final formats = {
    InputType.both: DateFormat("EEEE, MMMM d, yyyy 'at' h:mma"),
    InputType.date: DateFormat('yyyy-MM-dd'),
    InputType.time: DateFormat("HH:mm"),
  };

  Widget build(BuildContext context) => Container(
      child: DateTimePickerFormField(
        inputType: InputType.both,
        editable: true,
        format: formats[inputType],
        decoration: InputDecoration(
            labelText: 'Date/Time', hasFloatingPlaceholder: false),
        onChanged: (dt) {
          setState(() => dateT = dt);
          Navigator.of(context).pop(dateT);
        },

      )


  );


}

I am not using the value result yet Because the error is that I never get to the add reminder page and it says that the result push navigation method is pointing at null

HeavenOSK · Accepted Answer · 2019-02-14 23:26:04Z

In this situation passing data with Navigator is not suitable. Because there isn't page transition between the page and your dateTime Widget. I recommend you to implement ValueChanged callback to pass data between widgets in same screen.

example code:

It's little bit tricky. But material.dart's widgets often use this technique. I hope this will help you!

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  DateTime dateT;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Add a Reminder'),
      ),
      body: new Container(
        padding: new EdgeInsets.all(20.0),
        child: new Form(
          child: new ListView(
            children: <Widget>[
              new TextFormField(
                keyboardType: TextInputType.text,
                // Use email input type for emails.
                decoration: new InputDecoration(
                  hintText: 'Title of reminder',
                ),
              ),
              dateTime(
                onDateTimeChanged: (newDateTime) {
                  dateT = newDateTime;
                },
              ),
              RaisedButton(
                child: Text('Save'),
                onPressed: () {
                  Navigator.pop(context);
                },
              )
            ],
          ),
        ),
      ),
    );
  }
}

class dateTime extends StatefulWidget {
  final ValueChanged<DateTime> onDateTimeChanged;

  dateTime({Key key, this.onDateTimeChanged}) : super(key: key);

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

class dateTimeState extends State<dateTime> {
  DateTime dateT;

  InputType inputType = InputType.both;

  final formats = {
    InputType.both: DateFormat("EEEE, MMMM d, yyyy 'at' h:mma"),
    InputType.date: DateFormat('yyyy-MM-dd'),
    InputType.time: DateFormat("HH:mm"),
  };

  Widget build(BuildContext context) => Container(
        child: DateTimePickerFormField(
          inputType: InputType.both,
          editable: true,
          format: formats[inputType],
          decoration: InputDecoration(
              labelText: 'Date/Time', hasFloatingPlaceholder: false),
          onChanged: (dt) {
            widget.onDateTimeChanged(dt);
          },
        ),
      );
}

(Btw your dateAndTimeWidget is a method, is not a Widget. So if you assign it to Column`s children(List), Flutter framework cannot understand.)

Umar Farooq · Accepted Answer · 2020-09-07 10:40:21Z

For more time saving solution for returning value from another widget and using it, here's an example for Flutter Dropdown:

import 'package:flutter/material.dart';
import 'package:paxi_ride/constant.dart';

class BuildDropdown extends StatefulWidget {
  final ValueChanged<String> onChanged;
  String defaultValue, selectedValue, dropdownHint;
  List<String> itemsList;

  BuildDropdown(
      {Key key,
      this.itemsList,
      this.defaultValue,
      this.dropdownHint,
      this.onChanged})
      : super(key: key);

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

class _BuildDropdownState extends State<BuildDropdown> {
  String _value;

  @override
  Widget build(BuildContext context) {
    return Container(
      // height: 40,
      padding: EdgeInsets.symmetric(horizontal: 16, vertical: 0),
      margin: EdgeInsets.symmetric(horizontal: 16, vertical: 8),
      color: Colors.white,
      child: DropdownButton<String>(
        items: widget.itemsList.map(
          (String value) {
            return new DropdownMenuItem<String>(
              value: value,
              child: new Text(value),
            );
          },
        ).toList(),
        value: _value == null ? widget.defaultValue : _value,
        isExpanded: true,
        onChanged: (String value) {
          setState(() {
            _value = value;
          });
          widget.onChanged(value);
        },
        hint: Text(widget.dropdownHint),
        style: TextStyle(
          fontSize: 14,
          color: brownColorApp,
        ),
        iconEnabledColor: brownColorApp,
        iconSize: 14,
        underline: Container(),
      ),
    );
  }
}

Call this widget from another widget where you want to get selected value like this:

String selectedValue; //class field

BuildDropdown(
          itemsList: ['Option 1','Option 2'],
          defaultValue: 'Option 1',
          dropdownHint: 'Select Required Option',
          onChanged: (value) {
            selectedValue = value;
          },
        ),

Use this value wherever needed, it will be changed as dropdown selection is changed.

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