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Flutter 初探

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剖析官方Demo

当我们安装好Fultter后，我们可以看见main.dart预置了一段代码，即官方的一个简单Demo，功能即一个简单的计数器，点击右下角的"+"，对应屏幕的数字也会增加，显示效果：

以下为源码：

import 'package:flutter/material.dart';

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

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

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text(widget.title),
      ),
      body: new Center(
        child: new Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            new Text(
              'You have pushed the button this many times:',
            ),
            new Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: new FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: new Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

简单增改：

以下为main.dart ：

// 导入Material UI组件库
import 'package:flutter/material.dart';
import 'package:english_words/english_words.dart';

// 应用程序入口，runApp功能即启动Flutter应用，接收的参数为Widget参数
void main() => runApp(new MyApp());

// 继承一个无状态Widget组件，MyApp类代表Flutter应用
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // MaterialApp 设置应用名称、主题、语言、首页及路由列表等，其本身也是个Widget组件
    return new MaterialApp(
      // 应用名称
      title: 'Flutter Demos',
      // 应用主题
      theme: new ThemeData(
        // 蓝色主题
        primarySwatch: Colors.blue,
      ),
      // 使用命名路由管理route，首先注册路由表
      routes: {
        "new_page": (context) => NewRoute(),
      },
      // 应用首页路由
      home: new MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

// 即继承一个有状态Widget组件
class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  // 对应该类的状态类
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  // “+” 次数记录
  int _counter = 0;

  // 设置状态的自增函数
  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  // 构建UI界面的逻辑build方法
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text(widget.title),
      ),
      body: new Center(
        child: new Column(
          mainAxisAlignment: MainAxisAlignment.center,
          // 泛型Widget，即接受Widget组件类型构建列表
          children: <Widget>[
            new Text(
              'You have pushed the button this many times:',
            ),
            new Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
            new Text('''显示文字
            可以多行
              书写
            '''),
            // 添加一个按钮组件，用于跳转新路由（新页面）
            FlatButton(
                child: Text('open new route'),
                textColor: Colors.blue,
                // 导航至新路由
                onPressed: () {
                  // 推至路由栈，路由管理Widget组件，通过栈来管理一个路由widget集合 即先进先出管理原则，这样好理解多了
                  // Navigator.push(context,
                  //   new MaterialPageRoute(builder: (context){
                  //     return new NewRoute();
                  // // 通过路由名称也可以打开新的路由页

                  //   },
                  //   )
                  // );
                  Navigator.pushNamed(context, "new_page");
                }),
            // 跳转至新路由的按钮
            FlatButton(
              child: Text('open new counter'),
              textColor: Colors.blue,
              onPressed: () => Navigator.pushNamed(context, "new_page"),
            ),
            // 通过english_words包随机显示一个英文单词
            new RandomWordsWidget(),
            // 打印文字的组件
            Echo(
              text: "接收输入文字并回显",
            )
          ],
        ),
      ),
      // 右下角的按钮
      floatingActionButton: new FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: new Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

// 根据路由管理，尝试新的页面构建：
class NewRoute extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        appBar: AppBar(title: Text('This is new route.')),
        body: Center(child: Text('nice route.')));
  }
}

class RandomWordsWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final wordPair = new WordPair.random();
    return new Padding(
        padding: const EdgeInsets.all(8.0),
        child: new Text(wordPair.toString()));
  }
}

class Echo extends StatelessWidget {
  const Echo({
    Key key,
    @required this.text,
    this.backgroundColor: Colors.grey,
  }) : super(key: key);
  final String text;
  final Color backgroundColor;

  @override
  Widget build(BuildContext context) {
    return Center(
        child: Container(
      color: backgroundColor,
      child: Text(text),
    ));
  }
}