Flutter基础语法

Flutter概要

        

Flutter目录结构

文件夹	作用
android	android 平台相关代码
ios	ios平台相关代码
lib	flutter相关代码，我们主要编写的代码就在这个文件夹中
test	用于存放测试的代码
pubspec.yaml	配置文件，一般存放一些第三方库的依赖

Flutter入口文件、入口方法

        每一个 flutter 项目的 lib 目录里面都有一个 main.dart 这个文件就是 flutter 的入口文件。

main.dart里面

void main() {
  runApp(const MyApp());
}

         其中的 main 方法是 dart 的入口方法。runApp 方法是 flutter 的入口方法。 MyApp 是自定义的一个组件。

单独的内容抽离成的一个组件

        在 Flutter 中自定义组件其实就是一个类，这个类需要继承 StatelessWidget/StatefulWidget

前期我们都继承 StatelessWidget。

• StatelessWidget 是无状态组件，状态不可变的 widget
• StatefulWidget 是有状态组件，持有的状态可能在 widget 生命周期改变

MaterialApp和Scaffold装饰APP

        MaterialApp 是一个方便的 Widget，它封装了应用程序实现 Material Design 所需要的

一些 Widget。一般作为顶层widget 使用。

常用的属性：

• home（主页）
• title（标题）
• color（颜色）
• theme（主题）
• routes（路由）

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.red,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

Scaffold 是 Material Design 布局结构的基本实现。此类提供了用于显示 drawer、snackbar和底部 sheet 的API。

Scaffold 有下面几个主要属性：

• appBar - 显示在界面顶部的一个 AppBar。
• body - 当前界面所显示的主要内容 Widget。
• drawer - 抽屉菜单控件。

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

  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headlineMedium,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

各类组件

Flutter Container 组件、Text组件

Flutter Container 组件

        

名称	功能
alignment	topCenter：顶部居中对齐 topLeft：顶部左对齐 topRight：顶部右对齐 center：水平垂直居中对齐 centerLeft：垂直居中水平居左对齐 centerRight：垂直居中水平居右对齐 bottomCenter 底部居中对齐 bottomLeft：底部居左对齐 bottomRight：底部居右对齐
decoration	decoration: BoxDecoration( color: Colors.blue, border: Border.all( color: Colors.red, width: 2.0, ), borderRadius: BorderRadius.all( Radius.circular(8.0) ) )
margin	margin 属性是表示 Container 与外部其他 组件的距离。 EdgeInsets.all(20.0),
padding	padding 就是 Container 的内边距，指 Container 边缘与 Child 之间的距离 padding: EdgeInsets.all(10.0)
transform	让 Container 容易进行一些旋转之类 transform: Matrix4.rotationZ(0.2)
height	容器高度
width	容器宽度
child	容器子元素

import'package:flutter/material.dart';

 void main(){ 
  runApp(MyApp());
  }

  // 自定义主键
  class MyApp extends StatelessWidget{
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text("Flutter Demo"),
        ),
        body: BodyConent(),
      ),
    );
  }
    

  }

  // 内容组件
  class BodyConent extends StatelessWidget{
  @override
  Widget build(BuildContext context) {
    return Center(
      child: Container(              
      //child 容器元素
      child:Text("欢迎来到Flutter"),
      // 装饰
      // 背景 颜色浅蓝色
      decoration: BoxDecoration(color: Color.fromRGBO(100, 233, 244, 0.5), 
      // 圆角
      borderRadius: BorderRadius.all(Radius.circular(10.0))), 
      // 对齐方式
      alignment: Alignment.center,
      width: 300.0 ,
      height: 300.0,
      ),
    );

  }

  }

Flutter Text 组件 

        

名称	功能
textAlign	文本对齐方式（Center居中、left左对齐、right右对齐、justfy两端对齐）
textDirection	文本方向（ltr从左至右、rtl从右到左）
overflow	文字超出屏幕之后的处理方式（clip裁剪、fade渐隐、ellipsis省略）
textScaleFactor	字体显示倍率
maxLines	文字显示最大行数
style	字体的样式设置

TextStyle的参数

名称	功能
decoration	文字装饰线（none 没有线，lineThrough 删 除线，overline 上划线，underline 下划线）
decorationColor	文字装饰线颜色
decorationStyle	文字装饰线风格（[dashed,dotted]虚线， double 两根线，solid 一根实线，wavy 波浪线）
wordSpacing	单词间隙（如果是负值，会让单词变得更紧 凑
letterSpacing	字母间隙（如果是负值，会让字母变得更紧 凑）
fontStyle	文字样式（italic 斜体，normal 正常体
fontSize	文字大小
color	文字颜色
fontWeight	字体粗细（bold 粗体，normal 正常体）

import'package:flutter/material.dart';

 void main(){ 
  runApp(MyApp());
  }

  // 自定义主键
  class MyApp extends StatelessWidget{
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text("Flutter Demo"),
        ),