Flutter Provider sample

main.dart

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:flutterapp/model/user.dart';
import 'package:intl/intl.dart';
import 'package:provider/provider.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        ChangeNotifierProvider(
          create: (context) =>
              User(
                  'Tony Stark', DateTime.parse('1970-05-29'), 'Billionaire',
                  720),
        ),
      ],
      child: MaterialApp(
        title: 'Flutter Demo',
        theme: ThemeData(
          primarySwatch: Colors.blue,
        ),
        home: MyWidget(),
      ),
    );
  }
}

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final user = Provider.of<User>(context);

    final inputBorder = OutlineInputBorder(
        borderSide: BorderSide(color: Theme
            .of(context)
            .primaryColor));

    final dobController = TextEditingController(
        text: user.dateOfBirth.toIso8601String().substring(0, 10));

    return Scaffold(
      appBar: AppBar(
        title: Text('Flutter Demo Home Page'),
      ),
      body: Center(
        child: Container(
          padding: EdgeInsets.all(16),
          child: Column(
            mainAxisAlignment: MainAxisAlignment.start,
            children: <Widget>[
              TextFormField(
                initialValue: user.name,
                decoration: InputDecoration(
                  labelText: 'Name',
                  enabledBorder: inputBorder,
                  focusedBorder: inputBorder,
                ),
                onChanged: (text) {
                  user.name = text;
                },
              ),
              SizedBox(height: 10),
              TextFormField(
                initialValue: user.job,
                decoration: InputDecoration(
                  labelText: 'Job',
                  enabledBorder: inputBorder,
                  focusedBorder: inputBorder,
                ),
                onChanged: (text) {
                  user.job = text;
                },
              ),
              SizedBox(height: 10),
              TextFormField(
                decoration: InputDecoration(
                  labelText: 'Date of Birth',
                  enabledBorder: inputBorder,
                  focusedBorder: inputBorder,
                ),
                controller: dobController,
                onTap: () async {
                  final date = await showDatePicker(
                      context: context,
                      initialDate: user.dateOfBirth,
                      firstDate: DateTime.parse('1970-01-01'),
                      lastDate: DateTime.now());
                  if (date != null) {
                    user.dateOfBirth = date;
                    dobController.text =
                        date.toIso8601String().substring(0, 10);
                  }
                },
              ),
              SizedBox(height: 10),
              TextFormField(
                initialValue: '${user.money}',
                decoration: InputDecoration(
                  labelText: 'Money',
                  enabledBorder: inputBorder,
                  focusedBorder: inputBorder,
                ),
                inputFormatters: [WhitelistingTextInputFormatter.digitsOnly],
                onChanged: (text) {
                  if (text.length > 0) {
                    user.money = int.parse(text);
                  } else {
                    user.money = 0;
                  }
                },
              ),
              SizedBox(height: 50),
              Preview()
            ],
          ),
        ),
      ),
    );
  }
}

class Preview extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Card(color: Colors.red, elevation: 10,
        child: Padding(padding: EdgeInsets.all(16), child: PreviewChild1()));
  }
}

class PreviewChild1 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Card(color: Colors.blue, elevation: 10,
        child: Padding(padding: EdgeInsets.all(16), child: PreviewChild2()));
  }
}

class PreviewChild2 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Card(color: Colors.green, elevation: 10,
        child: Padding(padding: EdgeInsets.all(16), child: PreviewChild3()));
  }
}

class PreviewChild3 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final user = Provider.of<User>(context);
    final f = NumberFormat('#,###', 'en_US');

    return Card(
      elevation: 5,
      child: Padding(
          padding: EdgeInsets.all(16),
          child: Column(
            children: <Widget>[
              Text('Name: ${user.name}'),
              Text(
                  'Name: ${user.dateOfBirth.toIso8601String().substring(
                      0, 10)}'),
              Text('Job: ${user.job}'),
              Text('Money: \$${f.format(user.money)}'),
            ],
          )),
    );
  }
}

pubspec.yml

name: flutterapp
description: A new Flutter application.

# The following defines the version and build number for your application.
# A version number is three numbers separated by dots, like 1.2.43
# followed by an optional build number separated by a +.
# Both the version and the builder number may be overridden in flutter
# build by specifying --build-name and --build-number, respectively.
# In Android, build-name is used as versionName while build-number used as versionCode.
# Read more about Android versioning at https://developer.android.com/studio/publish/versioning
# In iOS, build-name is used as CFBundleShortVersionString while build-number used as CFBundleVersion.
# Read more about iOS versioning at
# https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html
version: 1.0.0+1

environment:
  sdk: ">=2.1.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter

  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^0.1.2

  provider: ^4.0.2
  intl: ^0.16.1

dev_dependencies:
  flutter_test:
    sdk: flutter


# For information on the generic Dart part of this file, see the
# following page: https://dart.dev/tools/pub/pubspec

# The following section is specific to Flutter.
flutter:

  # The following line ensures that the Material Icons font is
  # included with your application, so that you can use the icons in
  # the material Icons class.
  uses-material-design: true

  # To add assets to your application, add an assets section, like this:
  # assets:
  #  - images/a_dot_burr.jpeg
  #  - images/a_dot_ham.jpeg

  # An image asset can refer to one or more resolution-specific "variants", see
  # https://flutter.dev/assets-and-images/#resolution-aware.

  # For details regarding adding assets from package dependencies, see
  # https://flutter.dev/assets-and-images/#from-packages

  # To add custom fonts to your application, add a fonts section here,
  # in this "flutter" section. Each entry in this list should have a
  # "family" key with the font family name, and a "fonts" key with a
  # list giving the asset and other descriptors for the font. For
  # example:
  # fonts:
  #   - family: Schyler
  #     fonts:
  #       - asset: fonts/Schyler-Regular.ttf
  #       - asset: fonts/Schyler-Italic.ttf
  #         style: italic
  #   - family: Trajan Pro
  #     fonts:
  #       - asset: fonts/TrajanPro.ttf
  #       - asset: fonts/TrajanPro_Bold.ttf
  #         weight: 700
  #
  # For details regarding fonts from package dependencies,
  # see https://flutter.dev/custom-fonts/#from-packages

user.dart

import 'package:flutter/material.dart';

class User with ChangeNotifier {
  String _name = '';
  DateTime _dateOfBirth;
  String _job = '';
  int _money = 0;

  User(this._name, this._dateOfBirth, this._job, this._money);
  String get name => _name;
  DateTime get dateOfBirth => _dateOfBirth;
  String get job => _job;
  int get money => _money;

  set name(String name) {
    _name = name;
    notifyListeners();
  }
  set dateOfBirth(DateTime dateOfBirth) {
    _dateOfBirth = dateOfBirth;
    notifyListeners();
  }
  set job(String job) {
    _job = job;
    notifyListeners();
  }
  set money(int money) {
    _money = money;
    notifyListeners();
  }
}