update checkbox and return value from dialog in flutter

Question

I am trying to add some city list to a dialog with checkbox so that i need to implement multiple click on items. what I am trying to do is given below.

onPressed from button calls Rest Service and on success result I just show a dialog

void showCityDialog(BuildContext context) {
    SimpleDialog dialog = new SimpleDialog(
      title: Row(
        mainAxisAlignment: MainAxisAlignment.spaceBetween,
        children: <Widget>[
          new Text(
            "CITIES",
            style: TextStyle(fontSize: 18.0, color: Colors.black),
            textAlign: TextAlign.center,
          ),
          new RaisedButton(
            onPressed: () {print("clicked");},
            color: Color(0xFFfab82b),
            child: new Text(
              "Done",
              style: TextStyle(color: Colors.white),
            ),)],),
      children: <Widget>[
        Column(
          mainAxisAlignment: MainAxisAlignment.start,
          crossAxisAlignment: CrossAxisAlignment.start,
          children: <Widget>[
            new Container(
              constraints: BoxConstraints(maxHeight: 500.0),
              child: ListView.builder(
                scrollDirection: Axis.vertical,
                itemCount: cityData.length,
                itemBuilder: (context, position) {
                  return new CheckboxListTile(
                    value: checkboxValueCity,
                    onChanged: (bool value) {
                      setState(() {
                        checkboxValueCity = value;
                      });
                    },
                    activeColor: Color(0xFFfab82b),
                    dense: true,
                    title: Text(
                      cityData[position].city_name,
                      style: TextStyle(fontSize: 16.0, color: Colors.black),
                    ),);},),),],)],);
    showDialog(
        context: context,
        builder: (BuildContext context) {
          return dialog;
        });
  }

checkboxValueCity is a boolean variable in class , on click of chekboxListItem i need to update checkbox value as checked and uncheced. At the same time need to add/remove that item to a list which is also inside that class.

But in my code checkbox is not refershing on every click but when i close that box and open it again checkbox is checked. then how can i get multiple click from tile and how can i return list from dialog?

Answer 1

Your dialog needs to be a StatefulWidget (Flutter Github issue). The member variable that tracks selection state needs to be in the dialog class. You can use a callback to update a member variable in your parent class with the List of selected cities. There also seem to be some issues using a ListView.builder inside of a SimpleDialog or AlertDialog (search the Flutter Github for issues) so I used a plain Dialog.

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Checkbox Dialog Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Checkbox Dialog Demo'),
    );
  }
}

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

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

class _MyHomePageState extends State<MyHomePage> {
  bool checkboxValueCity = false;
  List<String> allCities = ['Alpha', 'Beta', 'Gamma'];
  List<String> selectedCities = [];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      floatingActionButton: FloatingActionButton(
          child: Icon(Icons.add),
          onPressed: () {
            showDialog(
                context: context,
                builder: (context) {
                  return _MyDialog(
                      cities: allCities,
                      selectedCities: selectedCities,
                      onSelectedCitiesListChanged: (cities) {
                        selectedCities = cities;
                        print(selectedCities);
                      });
                });
          }),
    );
  }
}

class _MyDialog extends StatefulWidget {
  _MyDialog({
    this.cities,
    this.selectedCities,
    this.onSelectedCitiesListChanged,
  });

  final List<String> cities;
  final List<String> selectedCities;
  final ValueChanged<List<String>> onSelectedCitiesListChanged;

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

class _MyDialogState extends State<_MyDialog> {
  List<String> _tempSelectedCities = [];

  @override
  void initState() {
    _tempSelectedCities = widget.selectedCities;
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Dialog(
      child: Column(
        children: <Widget>[
          Row(
            mainAxisAlignment: MainAxisAlignment.spaceBetween,
            children: <Widget>[
              Text(
                'CITIES',
                style: TextStyle(fontSize: 18.0, color: Colors.black),
                textAlign: TextAlign.center,
              ),
              RaisedButton(
                onPressed: () {
                  Navigator.pop(context);
                },
                color: Color(0xFFfab82b),
                child: Text(
                  'Done',
                  style: TextStyle(color: Colors.white),
                ),
              ),
            ],
          ),
          Expanded(
            child: ListView.builder(
                itemCount: widget.cities.length,
                itemBuilder: (BuildContext context, int index) {
                  final cityName = widget.cities[index];
                  return Container(
                    child: CheckboxListTile(
                        title: Text(cityName),
                        value: _tempSelectedCities.contains(cityName),
                        onChanged: (bool value) {
                          if (value) {
                            if (!_tempSelectedCities.contains(cityName)) {
                              setState(() {
                                _tempSelectedCities.add(cityName);
                              });
                            }
                          } else {
                            if (_tempSelectedCities.contains(cityName)) {
                              setState(() {
                                _tempSelectedCities.removeWhere(
                                    (String city) => city == cityName);
                              });
                            }
                          }
                          widget
                              .onSelectedCitiesListChanged(_tempSelectedCities);
                        }),
                  );
                }),
          ),
        ],
      ),
    );
  }
}

Answer 2

Use StatefulBuilder to update Widgets only inside Dialog. StatefulBuilder is best for update sebsection of the widget tree where state is needed.

simple code snippet

    void _showDialog() {
    showDialog(
      context: context,
      builder: (context) {
        return StatefulBuilder( // StatefulBuilder
          builder: (context, setState) {
            return AlertDialog(
              actions: <Widget>[
                Container(
                  width: 400,
                    child: Column(
                      crossAxisAlignment: CrossAxisAlignment.center,
                      children: <Widget>[
                        Text(
                          "Student Attendence",
                          style: TextStyle(fontSize: 20),
                        ),
                        SizedBox(
                          height: 5,
                        ),
                        Container(
                          height: 2,
                          color: Colors.black,
                        ),
                        SizedBox(
                          height: 15,
                        ),
                      CheckboxListTile(
                        value: user1,
                        title: Text("user1"),
                        onChanged: (value){
                          setState(() {
                            user1=value;
                          });
                        },
                      ),
                        Divider(
                          height: 10,
                        ),
                        CheckboxListTile(
                          value: user2,
                          title: Text("user2"),
                          onChanged: (value){
                            setState(() {
                              user2=value;
                            });
                          },
                        ),
                        Divider(
                          height: 10,
                        ),
                        CheckboxListTile(
                          value: user3,
                          title: Text("user3"),
                          onChanged: (value){
                            setState(() {
                              user3=value;
                            });
                          },
                        ),
                        Divider(
                          height: 10,
                        ),
                        CheckboxListTile(
                          value: user4,
                          title: Text("user4"),
                          onChanged: (value){
                            setState(() {
                              user4=value;
                            });
                          },
                        ),
                        Divider(
                          height: 10,
                        ),

                        SizedBox(
                          height: 5,
                        ),
                        Row(
                          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                          children: <Widget>[
                            Material(
                              elevation: 5.0,
                              color: Colors.blue[900],
                              child: MaterialButton(
                                padding: EdgeInsets.fromLTRB(
                                    10.0, 5.0, 10.0, 5.0),
                                onPressed: () {},
                                child: Text("Save",
                                    textAlign: TextAlign.center,
                                    style: TextStyle(
                                      color: Colors.white,
                                      fontSize: 15,
                                    )),
                              ),
                            ),
                            Material(
                              elevation: 5.0,
                              color: Colors.blue[900],
                              child: MaterialButton(
                                padding: EdgeInsets.fromLTRB(
                                    10.0, 5.0, 10.0, 5.0),
                                onPressed: () {
                                  setState(() {
                                    Navigator.of(context).pop();
                                  });
                                },
                                child: Text("Cancel",
                                    textAlign: TextAlign.center,
                                    style: TextStyle(
                                      color: Colors.white,
                                      fontSize: 15,
                                    )),
                              ),
                            ),
                            Material(
                              elevation: 5.0,
                              color: Colors.blue[900],
                              child: MaterialButton(
                                padding: EdgeInsets.fromLTRB(
                                    10.0, 5.0, 10.0, 5.0),
                                onPressed: () {},
                                child: Text("Select All",
                                    textAlign: TextAlign.center,
                                    style: TextStyle(
                                      color: Colors.white,
                                      fontSize: 15,
                                    )),
                              ),
                            ),
                          ],
                        )
                      ],
                    ))
              ],
            );
          },
        );
      },
    );
  }

example