How To Set Up Progress Indicator In Flutter Android App

import 'package:flutter/material.dart';
import 'dart:async';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Flutter Progress Indicator Demo',
      theme: new ThemeData(
        primarySwatch: Colors.pink,
      ),
      home: new MyHomePage(),
    );
  }
}

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

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        appBar: new AppBar(
          title: new Text("Progress Indicator Demo"),
          backgroundColor: Colors.pink,
        ),
        drawer: new Drawer(
          child: new ListView(
            children: <Widget>[
              new ListTile(
                title: new Text("WELCOME"),
              ),
              new Divider(),
              new ListTile(
                  title: new Text("Settings"),
                  trailing: new Icon(Icons.settings),
                  onTap: () {
                    Navigator.of(context).pop();
                    Navigator.push(
                        context,
                        new MaterialPageRoute(
                            builder: (context) => new SettingsPage()));
                  }),
            ],
          ),
        ),
        body: new Center(
          child: new Text("Home Page", style: new TextStyle(fontSize: 25.0)),
        ));
  }
}

class SettingsPage extends StatefulWidget {
  @override
  _SettingsPageState createState() => new _SettingsPageState();
}

class _SettingsPageState extends State<SettingsPage> {
  bool _monitor = true;
  bool _network = false;
  bool _blutooth = false;
  bool _apps = false;
  bool _sound = false;
  bool _time = false;
  bool _accounts = false;
  bool _access = false;
  bool _saving = false;
  bool _help = false;

  void _submit() {
    print('submit called...');

    setState(() {
      _saving = true;
    });

    //Simulate a service call
    print('submitting to backend...');
    new Future.delayed(new Duration(seconds: 4), () {
      setState(() {
        _saving = false;
      });
    });
  }

  List<Widget> _buildForm(BuildContext context) {
    Form form = new Form(
      child: new Column(
        children: [
          new CheckboxListTile(
            title: const Text('Enable Monitoring?'),
            value: _monitor,
            onChanged: (bool value) {
              setState(() {
                _monitor = value;
              });
            },
            secondary: const Icon(Icons.power),
          ),
          new SwitchListTile(
            title: const Text('Network'),
            value: _network,
            onChanged: (bool value) {
              setState(() {
                _network = value;
              });
            },
            secondary: const Icon(Icons.network_cell),
          ),
          new SwitchListTile(
            title: const Text('Blutooth'),
            value: _blutooth,
            onChanged: (bool value) {
              setState(() {
                _blutooth = value;
              });
            },
            secondary: const Icon(Icons.bluetooth_connected),
          ),
          new SwitchListTile(
            title: const Text('Apps'),
            value: _apps,
            onChanged: (bool value) {
              setState(() {
                _apps = value;
              });
            },
            secondary: const Icon(Icons.apps),
          ),
          new SwitchListTile(
            title: const Text('Sound'),
            value: _sound,
            onChanged: (bool value) {
              setState(() {
                _sound = value;
              });
            },
            secondary: const Icon(Icons.surround_sound),
          ),
          new SwitchListTile(
            title: const Text('Time'),
            value: _time,
            onChanged: (bool value) {
              setState(() {
                _time = value;
              });
            },
            secondary: const Icon(Icons.timer),
          ),
          new SwitchListTile(
            title: const Text('Accounts'),
            value: _accounts,
            onChanged: (bool value) {
              setState(() {
                _accounts = value;
              });
            },
            secondary: const Icon(Icons.account_balance),
          ),
          new SwitchListTile(
            title: const Text('Accessibility'),
            value: _access,
            onChanged: (bool value) {
              setState(() {
                _access = value;
              });
            },
            secondary: const Icon(Icons.accessibility),
          ),
          new SwitchListTile(
            title: const Text('Help'),
            value: _help,
            onChanged: (bool value) {
              setState(() {
                _help = value;
              });
            },
            secondary: const Icon(Icons.help),
          ),
          new RaisedButton(
            color: Colors.pink,
            onPressed: _submit,
            child: new Text('Save',style: TextStyle(color: Colors.white),),
          ),
        ],
      ),
    );

    var l = new List<Widget>();
    l.add(form);

    if (_saving) {
      var modal = new Stack(
        children: [
          new Opacity(
            opacity: 0.3,
            child: const ModalBarrier(dismissible: false, color: Colors.grey),
          ),
          new Center(
            child: new CircularProgressIndicator(),
          ),
        ],
      );
      l.add(modal);
    }

    return l;
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Settings'),
        backgroundColor: Colors.pink,
      ),
      body: new Stack(
        children: _buildForm(context),
      ),
    );
  }
}