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1 : import 'package:flutter/material.dart'; 2 : 3 0 : void main() { 4 0 : runApp(const MyApp()); 5 : } 6 : 7 : class MyApp extends StatelessWidget { 8 2 : const MyApp({Key? key}) : super(key: key); 9 : 10 : // This widget is the root of your application. 11 1 : @override 12 : Widget build(BuildContext context) { 13 1 : return MaterialApp( 14 : title: 'Flutter Demo', 15 1 : theme: ThemeData( 16 : // This is the theme of your application. 17 : // 18 : // Try running your application with "flutter run". You'll see the 19 : // application has a blue toolbar. Then, without quitting the app, try 20 : // changing the primarySwatch below to Colors.green and then invoke 21 : // "hot reload" (press "r" in the console where you ran "flutter run", 22 : // or simply save your changes to "hot reload" in a Flutter IDE). 23 : // Notice that the counter didn't reset back to zero; the application 24 : // is not restarted. 25 : primarySwatch: Colors.blue, 26 : ), 27 : home: const MyHomePage(title: 'Flutter Demo Home Page'), 28 : ); 29 : } 30 : } 31 : 32 : class MyHomePage extends StatefulWidget { 33 1 : const MyHomePage({Key? key, required this.title}) : super(key: key); 34 : 35 : // This widget is the home page of your application. It is stateful, meaning 36 : // that it has a State object (defined below) that contains fields that affect 37 : // how it looks. 38 : 39 : // This class is the configuration for the state. It holds the values (in this 40 : // case the title) provided by the parent (in this case the App widget) and 41 : // used by the build method of the State. Fields in a Widget subclass are 42 : // always marked "final". 43 : 44 : final String title; 45 : 46 1 : @override 47 1 : State<MyHomePage> createState() => _MyHomePageState(); 48 : } 49 : 50 : class _MyHomePageState extends State<MyHomePage> { 51 : int _counter = 0; 52 : 53 1 : void _incrementCounter() { 54 2 : setState(() { 55 : // This call to setState tells the Flutter framework that something has 56 : // changed in this State, which causes it to rerun the build method below 57 : // so that the display can reflect the updated values. If we changed 58 : // _counter without calling setState(), then the build method would not be 59 : // called again, and so nothing would appear to happen. 60 2 : _counter++; 61 : }); 62 : } 63 : 64 1 : @override 65 : Widget build(BuildContext context) { 66 : // This method is rerun every time setState is called, for instance as done 67 : // by the _incrementCounter method above. 68 : // 69 : // The Flutter framework has been optimized to make rerunning build methods 70 : // fast, so that you can just rebuild anything that needs updating rather 71 : // than having to individually change instances of widgets. 72 1 : return Scaffold( 73 1 : appBar: AppBar( 74 : // Here we take the value from the MyHomePage object that was created by 75 : // the App.build method, and use it to set our appbar title. 76 3 : title: Text(widget.title), 77 : ), 78 1 : body: Center( 79 : // Center is a layout widget. It takes a single child and positions it 80 : // in the middle of the parent. 81 1 : child: Column( 82 : // Column is also a layout widget. It takes a list of children and 83 : // arranges them vertically. By default, it sizes itself to fit its 84 : // children horizontally, and tries to be as tall as its parent. 85 : // 86 : // Invoke "debug painting" (press "p" in the console, choose the 87 : // "Toggle Debug Paint" action from the Flutter Inspector in Android 88 : // Studio, or the "Toggle Debug Paint" command in Visual Studio Code) 89 : // to see the wireframe for each widget. 90 : // 91 : // Column has various properties to control how it sizes itself and 92 : // how it positions its children. Here we use mainAxisAlignment to 93 : // center the children vertically; the main axis here is the vertical 94 : // axis because Columns are vertical (the cross axis would be 95 : // horizontal). 96 : mainAxisAlignment: MainAxisAlignment.center, 97 1 : children: <Widget>[ 98 : const Text( 99 : 'You have pushed the button this many times:', 100 : ), 101 1 : Text( 102 2 : '$_counter', 103 3 : style: Theme.of(context).textTheme.headline4, 104 : ), 105 : ], 106 : ), 107 : ), 108 1 : floatingActionButton: FloatingActionButton( 109 1 : onPressed: _incrementCounter, 110 : tooltip: 'Increment', 111 : child: const Icon(Icons.add), 112 : ), // This trailing comma makes auto-formatting nicer for build methods. 113 : ); 114 : } 115 : }