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1 : import 'package:flutter/material.dart'; 2 : 3 0 : void main() { 4 0 : runApp(MyApp()); 5 : } 6 : 7 : class MyApp extends StatelessWidget { 8 : // This widget is the root of your application. 9 1 : @override 10 : Widget build(BuildContext context) { 11 1 : return MaterialApp( 12 : title: 'Flutter Demo', 13 1 : theme: ThemeData( 14 : // This is the theme of your application. 15 : // 16 : // Try running your application with "flutter run". You'll see the 17 : // application has a blue toolbar. Then, without quitting the app, try 18 : // changing the primarySwatch below to Colors.green and then invoke 19 : // "hot reload" (press "r" in the console where you ran "flutter run", 20 : // or simply save your changes to "hot reload" in a Flutter IDE). 21 : // Notice that the counter didn't reset back to zero; the application 22 : // is not restarted. 23 : primarySwatch: Colors.blue, 24 : ), 25 1 : home: MyHomePage(title: 'Flutter Demo Home Page'), 26 : ); 27 : } 28 : } 29 : 30 : class MyHomePage extends StatefulWidget { 31 2 : MyHomePage({Key? key, required this.title}) : super(key: key); 32 : 33 : // This widget is the home page of your application. It is stateful, meaning 34 : // that it has a State object (defined below) that contains fields that affect 35 : // how it looks. 36 : 37 : // This class is the configuration for the state. It holds the values (in this 38 : // case the title) provided by the parent (in this case the App widget) and 39 : // used by the build method of the State. Fields in a Widget subclass are 40 : // always marked "final". 41 : 42 : final String title; 43 : 44 1 : @override 45 1 : _MyHomePageState createState() => _MyHomePageState(); 46 : } 47 : 48 : class _MyHomePageState extends State<MyHomePage> { 49 : int _counter = 0; 50 : 51 1 : void _incrementCounter() { 52 2 : setState(() { 53 : // This call to setState tells the Flutter framework that something has 54 : // changed in this State, which causes it to rerun the build method below 55 : // so that the display can reflect the updated values. If we changed 56 : // _counter without calling setState(), then the build method would not be 57 : // called again, and so nothing would appear to happen. 58 2 : _counter++; 59 : }); 60 : } 61 : 62 1 : @override 63 : Widget build(BuildContext context) { 64 : // This method is rerun every time setState is called, for instance as done 65 : // by the _incrementCounter method above. 66 : // 67 : // The Flutter framework has been optimized to make rerunning build methods 68 : // fast, so that you can just rebuild anything that needs updating rather 69 : // than having to individually change instances of widgets. 70 1 : return Scaffold( 71 1 : appBar: AppBar( 72 : // Here we take the value from the MyHomePage object that was created by 73 : // the App.build method, and use it to set our appbar title. 74 3 : title: Text(widget.title), 75 : ), 76 1 : body: Center( 77 : // Center is a layout widget. It takes a single child and positions it 78 : // in the middle of the parent. 79 1 : child: Column( 80 : // Column is also a layout widget. It takes a list of children and 81 : // arranges them vertically. By default, it sizes itself to fit its 82 : // children horizontally, and tries to be as tall as its parent. 83 : // 84 : // Invoke "debug painting" (press "p" in the console, choose the 85 : // "Toggle Debug Paint" action from the Flutter Inspector in Android 86 : // Studio, or the "Toggle Debug Paint" command in Visual Studio Code) 87 : // to see the wireframe for each widget. 88 : // 89 : // Column has various properties to control how it sizes itself and 90 : // how it positions its children. Here we use mainAxisAlignment to 91 : // center the children vertically; the main axis here is the vertical 92 : // axis because Columns are vertical (the cross axis would be 93 : // horizontal). 94 : mainAxisAlignment: MainAxisAlignment.center, 95 1 : children: <Widget>[ 96 1 : Text( 97 : 'You have pushed the button this many times:', 98 : ), 99 1 : Text( 100 2 : '$_counter', 101 3 : style: Theme.of(context).textTheme.headline4, 102 : ), 103 : ], 104 : ), 105 : ), 106 1 : floatingActionButton: FloatingActionButton( 107 1 : onPressed: _incrementCounter, 108 : tooltip: 'Increment', 109 1 : child: Icon(Icons.add), 110 : ), // This trailing comma makes auto-formatting nicer for build methods. 111 : ); 112 : } 113 : }