Flutter学习1 - Android开发者快速上手

2024-02-21 10:56:01
开发
22

1、对应关系

概念对应关系

	Android	Flutter
页面	Activity和Fragment	Widget
视图	View	Widget
页面跳转	Intent	Navigater
网络库	okHttp	http
数据存储	SharedPreference和SQLite	shared_preferences和sqflite

布局对应关系

	Android	Flutter
布局文件	xml	Widget
线性布局	LinearLayout	Row和Column widget
相对布局	RelativeLayout	组合使用Column、Row和Stack Widget
文本框	TextView	text
输入框	EditText	TextField

滚动列表对应关系

	Android	Flutter
布局文件	xml	Widget
滚动视图	ScrollView	ListView
列表	ListView	ListView
列表	RecyclerView	ListView.builder

2、快速上手布局开发

（1）更新 Widget 状态

在这里插入图片描述

import 'package:flutter/material.dart';

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

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

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

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

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
   
  String tips = "";

  @override
  Widget build(BuildContext context) {
   
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Text(tips),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _updateTips,
        tooltip: 'Update',
        child: const Icon(Icons.add),
      ),
    );
  }

  //更新布局 widgets
  //类似android中 setText
  void _updateTips() {
   
    //我们无法改变widget，因为 Flutter 中 widget 是不可变的
    //但是可以通过 setState 改变 widget状态
    setState(() {
   
      tips = "快速上手 Flutter";
    });
  }
}

在body中添加一个Text，其取值为 tips
按钮的点击事件 _updateTips() 中，通过 setState() 改变 tips 的值，从而更新 widget 状态

该示例类似于 android 中的 textView.setText(tips)

（2）布局中添加/删除一个 Widget

在这里插入图片描述

import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
   
    return MaterialApp(
      title: 'muke flutter',
      theme: ThemeData(
        primarySwatch: Colors.red,
      ),
      home: const MyHomePage(title: 'muke learning'),
    );
  }
}

class MyHomePage extends StatefulWidget {
   
  const MyHomePage({
   super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
   

  bool _toggle = true;

  get _dyWidget => _toggle ? const Text("Widget 1") : const Text("Widget 2");

  @override
  Widget build(BuildContext context) {
   
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: _dyWidget,
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _updateWidget,
        tooltip: 'Update',
        child: const Icon(Icons.add),
      ),
    );
  }

  //在布局中添加/删除一个 widget
  //类似安卓中 addView、removeView
  void _updateWidget() {
   
    setState(() {
   
      _toggle = !_toggle;
    });
  }
}

body中添加一个 Text，这个 Text 会根据 _toggle 的值变换，Text(“Widget 1”)或Text(“Widget 2”)
按钮点击事件 _updateWidget() 通过 setState() 更改 _toggle 的值，从而实现更换 widget 效果

（3）创建自定义 Widget

在这里插入图片描述

import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
   
    return MaterialApp(
      title: 'muke flutter',
      theme: ThemeData(
        primarySwatch: Colors.red,
      ),
      home: const MyHomePage(title: 'muke learning'),
    );
  }
}

class MyHomePage extends StatefulWidget {
   
  const MyHomePage({
   super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
   

  @override
  Widget build(BuildContext context) {
   
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: const Center(
        child: TipsWidget(),
      ),
    );
  }
}

//自定义 Widget
class TipsWidget extends StatelessWidget {
   
  const TipsWidget({
   super.key});

  @override
  Widget build(BuildContext context) {
   
    return const Text("自定义 Widget");
  }
}

自定义 TipsWidget，然后添加至 body 中

（4）添加一个滚动列表

在这里插入图片描述

import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
   
    return MaterialApp(
      title: 'muke flutter',
      theme: ThemeData(
        primarySwatch: Colors.red,
      ),
      home: const MyHomePage(title: 'muke learning'),
    );
  }
}

class MyHomePage extends StatefulWidget {
   
  const MyHomePage({
   super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
   

  get _listView => ListView(
        children: const [
          Text("AAA"),
          Text("BBB"),
          Text("CCC"),
          Text("DDD"),
          Text(
            "EEE",
            style: TextStyle(fontSize: 230),
          )
        ],
      );

  @override
  Widget build(BuildContext context) {
   
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body:  Center(
        child: _listView,
      ),
    );
  }
}

添加一个 ListView，当超出屏幕时就会滚动

3、手势事件处理

（1）监听 Widget 手势

在这里插入图片描述

import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
   
    return MaterialApp(
      title: 'muke flutter',
      theme: ThemeData(
        primarySwatch: Colors.red,
      ),
      home: const MyHomePage(title: 'muke learning'),
    );
  }
}

class MyHomePage extends StatefulWidget {
   
  const MyHomePage({
   super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

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

  @override
  Widget build(BuildContext context) {
   
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: ElevatedButton(
          child: Text("click me : $_count"),
          onPressed: () {
   
            setState(() {
   
              _count++;
            });
          },
        ),
      ),
    );
  }
}

点击按钮实现 +1

（2）GestureDetector手势监听

在这里插入图片描述

import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
   
    return MaterialApp(
      title: 'muke flutter',
      theme: ThemeData(
        primarySwatch: Colors.red,
      ),
      home: const MyHomePage(title: 'muke learning'),
    );
  }
}

class MyHomePage extends StatefulWidget {
   
  const MyHomePage({
   super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

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

  @override
  Widget build(BuildContext context) {
   
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: GestureDetector(
          child: Text("click me : $_count"),
          onTap: () {
   
            setState(() {
   
              _count++;
            });
          },
          onLongPress: () {
   
            setState(() {
   
              _count = 0;
            });
          },
        ),
      ),
    );
  }
}

GestureDetetor 只是对 Text 添加了一个手势监听，没有按钮样式
onTap()：单机时，加一
onLongPress()：长按时，清零

4、进阶

（1）异步 UI

（2）页面跳转

（3）工程结构和资源文件

（4）网络请求

（5）数据存储

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