How do you store the DateTime value in Flutter TimePicker

Question

I am using the datetime_picker_formfield package ( https://pub.dev/packages/datetime_picker_formfield ) and want to create two datetime pickers that the user enters and then calculate the difference between them once the user submits.

I have added a controller to datetime as shown below, but I realize this is just a TextEditing Controller and not a datetime controller. How do I track the submitted datetime of the two fields and then get the difference of them when I submit the "Get Difference" button.

 Row(
                                children: <Widget>[
                                  Container(
                                    width: width*.5,
                                    child:  DateTimeField(
                                      controller: _startTimeController,
                                      decoration: InputDecoration(
                                        enabledBorder: UnderlineInputBorder(
                                          borderSide: BorderSide(color: Colors.white),
                                        ),
                                        focusedBorder: UnderlineInputBorder(
                                          borderSide: BorderSide(color: Colors.white),
                                        ),
                                      ),
                                      style: TextStyle(color: Colors.white, fontSize: 32),
                                      format: format,
                                      onShowPicker: (context, currentValue) async {
                                        final time = await showTimePicker(
                                          context: context,
                                          initialTime: TimeOfDay.fromDateTime(currentValue ?? DateTime.now()),
                                        );
                                        return DateTimeField.convert(time);
                                      },
                                    ),
                                  ),
                                ],
                              ),
                              Row(
                                children: <Widget>[
                                  Container(
                                    width: width*.5,
                                    child:  DateTimeField(
                                      controller: _startTimeController,
                                      decoration: InputDecoration(
//        suffixIcon: IconButton(icon: Icon(Icons.close, color: Colors.white,), onPressed: state.clear,),
                                        enabledBorder: UnderlineInputBorder(
                                          borderSide: BorderSide(color: Colors.white),
                                        ),
                                        focusedBorder: UnderlineInputBorder(
                                          borderSide: BorderSide(color: Colors.white),
                                        ),
                                      ),
//                                      initialValue: yesterday10pm,
                                      style: TextStyle(color: Colors.white, fontSize: 32),
                                      format: format,
                                      onShowPicker: (context, currentValue) async {
                                        final time = await showTimePicker(
                                          context: context,
                                          initialTime: TimeOfDay.fromDateTime(currentValue ?? DateTime.now()),
                                        );
                                        return DateTimeField.convert(time);
                                      },
                                    ),
                                  ),
                                ],
                              ),
                              Row(children: <Widget>[
                                RaisedButton(child: Text("Get Difference"), onPressed: () {
                                  print(_startTimeController);
                                  print(_endTimeController);
                                } ,)
                              ],)

---

Updated to include error code:

flutter: 2019-11-14 04:25 PM
flutter: 2019-11-14 10:34 PM
flutter: ══╡ EXCEPTION CAUGHT BY GESTURE ╞═══════════════════════════════════════════════════════════════════
flutter: The following FormatException was thrown while handling a gesture:
flutter: Invalid date format
flutter: 2019-11-14 04:25 PM

Answer 1

Yous code do not contains date information, so assume time difference use today.
You can change if you have a Date field

code snippet

RaisedButton(child: Text("Get Difference"), onPressed: () {
              var now = new DateTime.now();
              var formatter = new DateFormat('yyyy-MM-dd');
              String today = formatter.format(now);
              String startDateTime = "${today} ${_startTimeController.text}";
              String endDateTime = "${today} ${_endTimeController.text}";
              print(startDateTime);
              print(endDateTime);

              var parsedstartDateTime = DateTime.parse(startDateTime);
              var parsedendDateTime = DateTime.parse(endDateTime);

              Duration difference = parsedendDateTime .difference(parsedstartDateTime);
              print(' Days ${difference.inDays}');
              print(' Hours ${difference.inHours}');
              print(' Mins ${difference.inMinutes}');

            } ,)

working demo and output

I/flutter (22206): 2019-11-15 02:12
I/flutter (22206): 2019-11-15 08:18
I/flutter (22206):  Days 0
I/flutter (22206):  Hours 6
I/flutter (22206):  Mins 366

full code

import 'package:flutter/material.dart';
import 'package:datetime_picker_formfield/datetime_picker_formfield.dart';
import 'package:intl/intl.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  final format = DateFormat("HH:mm");
  TextEditingController _startTimeController = TextEditingController();
  TextEditingController _endTimeController = TextEditingController();

  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Column(
        children: <Widget>[
          Row(
            children: <Widget>[
              Container(
                color: Colors.deepOrangeAccent,
                width: 200,
                child:  DateTimeField(
                  controller: _startTimeController,
                  decoration: InputDecoration(
                    enabledBorder: UnderlineInputBorder(
                      borderSide: BorderSide(color: Colors.white),
                    ),
                    focusedBorder: UnderlineInputBorder(
                      borderSide: BorderSide(color: Colors.white),
                    ),
                  ),
                  style: TextStyle(color: Colors.white, fontSize: 32),
                  format: format,
                  onShowPicker: (context, currentValue) async {
                    final time = await showTimePicker(
                      context: context,
                      initialTime: TimeOfDay.fromDateTime(currentValue ?? DateTime.now()),
                    );
                    return DateTimeField.convert(time);
                  },
                ),
              ),
            ],
          ),
          Row(
            children: <Widget>[
              Container(
                color: Colors.blue,
                width: 200,
                child:  DateTimeField(
                  controller: _endTimeController,
                  decoration: InputDecoration(
//        suffixIcon: IconButton(icon: Icon(Icons.close, color: Colors.white,), onPressed: state.clear,),
                    enabledBorder: UnderlineInputBorder(
                      borderSide: BorderSide(color: Colors.white),
                    ),
                    focusedBorder: UnderlineInputBorder(
                      borderSide: BorderSide(color: Colors.white),
                    ),
                  ),
//                                      initialValue: yesterday10pm,
                  style: TextStyle(color: Colors.white, fontSize: 32),
                  format: format,
                  onShowPicker: (context, currentValue) async {
                    final time = await showTimePicker(
                      context: context,
                      initialTime: TimeOfDay.fromDateTime(currentValue ?? DateTime.now()),
                    );
                    return DateTimeField.convert(time);
                  },
                ),
              ),
            ],
          ),
          Row(children: <Widget>[
            RaisedButton(child: Text("Get Difference"), onPressed: () {
              var now = new DateTime.now();
              var formatter = new DateFormat('yyyy-MM-dd');
              String today = formatter.format(now);
              String startDateTime = "${today} ${_startTimeController.text}";
              String endDateTime = "${today} ${_endTimeController.text}";
              print(startDateTime);
              print(endDateTime);

              var parsedstartDateTime = DateTime.parse(startDateTime);
              var parsedendDateTime = DateTime.parse(endDateTime);

              Duration difference = parsedendDateTime .difference(parsedstartDateTime);
              print(' Days ${difference.inDays}');
              print(' Hours ${difference.inHours}');
              print(' Mins ${difference.inMinutes}');

            } ,)
          ],)
        ],
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

Answer 2

You can just wrap the contents of your dialog in StatefulBuilder. This makes the dialog's content stateful, so you can call setState().

StatefulBuilder(
    builder: (BuildContext context, StateSetter setState) {
    ...
    setState(()=>do something);