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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: RootPage(),
    );
  }
}

class RootPage extends StatefulWidget {
  @override
  _RootPageState createState() => _RootPageState();
}

class _RootPageState extends State<RootPage> {
  @override
  Widget build(BuildContext context) {
    // Set background color of the system status bar to ensure it visible.
    SystemChrome.setSystemUIOverlayStyle(SystemUiOverlayStyle.dark);

    return Scaffold(
      body: SafeArea(
        child: Center(
          child: Column(mainAxisAlignment: MainAxisAlignment.center, children: [
            Padding(
              padding: const EdgeInsets.only(left: 16.0, right: 16.0),
              child: Text('This page does not have AppBar.\nThe text color of the status bar should be dark.\n\n' +
                  'Go to Next Page and get back here, then check the text color.\n' +
                  'Expected result :: the color recovers to be dark.'),
            ),
            RaisedButton(
                child: Text('Next Page'),
                onPressed: () async {
                  await Navigator.push(context, MaterialPageRoute(builder: (BuildContext context) => SecondPage()));
                  // The following lines will have no effect in vain.
                  debugPrint('get back');
                  SystemChrome.setSystemUIOverlayStyle(SystemUiOverlayStyle.dark);
                  setState(() {});
                }),
            Padding(
              padding: const EdgeInsets.only(top: 16.0),
              child: Text('setState() triggers build()'),
            ),
            RaisedButton(
              child: Text('Call setState()'),
              onPressed: () => setState(() {}),
            ),
          ]),
        ),
      ),
    );
  }
}

class SecondPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("Text color of status bar is bright")),
      body: SafeArea(
        child: Center(
            child: Column(mainAxisAlignment: MainAxisAlignment.center, children: [
          Text("The AppBar in this page makes\nthe status bar text color bright.\nLet's get back to the previous page.")
        ])),
      ),
    );
  }
}