main.dart

import 'dart:async';

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

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

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

class MyHomePage extends StatefulWidget {
  @override
  State createState() => MyHomePageState();
}

class MyHomePageState extends State<MyHomePage> {
  SystemUiOverlayStyle _currentStyle = SystemUiOverlayStyle.light;

  void _changeColor(r, g, b) {
    setState(() {
      _currentStyle = SystemUiOverlayStyle.dark.copyWith(
        statusBarColor: Color.fromRGBO(r, g, b, 1.0),
      );
    });
  }

  void _showDialog() async {
    _changeColor(32, 205, 125);
    await Future.delayed(const Duration(seconds: 5));
    showDialog(
      context: context,
      builder: (BuildContext context) {
        return AlertDialog(
          title: const Text('Something went wrong!'),
          content: const Text('Be sure you are connected to the Device'),
          actions: [
            FlatButton(
              child: const Text('Ok'),
              onPressed: () {
                Navigator.pop(context);
                _changeColor(244, 128, 36);
              },
            ),
          ],
        );
      },
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: AnnotatedRegion(
        sized: false,
        value: _currentStyle,
        child: Container(
          height: MediaQuery.of(context).size.height,
          width: MediaQuery.of(context).size.width,
          child: RaisedButton(
            child: const Text('Change Color'),
            color: Color.fromRGBO(32, 205, 125, 1.0),
            onPressed: _showDialog,
          ),
        ),
      ),
    );
  }
}