Flutter demo #3, simple samples.

demo3.dart

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

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

class MyAppWidget extends StatefulWidget {
  @override
  _MyAppWidgetState createState() => _MyAppWidgetState();
}

class _MyAppWidgetState extends State<MyAppWidget> {
  Color stringColor = Colors.red;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: "My first Flutter App",
      home: Scaffold(
        appBar: AppBar(title: Text("My first Flutter App")),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Container(
                padding:
                    EdgeInsets.only(left: 20, right: 20, top: 40, bottom: 40),
                color: stringColor,
                child: Text("My first Flutter App",
                    style: TextStyle(color: Colors.white, fontSize: 30),
                    textDirection: TextDirection.ltr),
              ),
              Padding(
                padding: EdgeInsets.all(30),
              ),
              RaisedButton(
                onPressed: changeIt,
                textColor: Colors.white,
                color: Colors.blue,
                child: Text("Change!"),
              ),
            ],
          ),
        ),
      ),
    );
  }

  void changeIt() {
    setState(() {
      stringColor = Color.fromARGB(255, Random().nextInt(255),
          Random().nextInt(255), Random().nextInt(255));
//      stringColor = (stringColor == Colors.red) ? Colors.green : Colors.red;
    });
  }
}