Flutter笔记66：本地存储shared_preferences的简单使用

Flutter本地存储比较常用的插件shared_preferences，它其实就是对IOS的NSUserDefaults和安卓的SharedPreferences的分别实现，这里是简单用法示例：

1、在pubspec.yaml中安装

shared_preferences: ^0.5.12+2

2、读取方法如：

void initFromCache() async{
    final SharedPreferences prefs = await _prefs;
    final value_nickname = prefs.getString('key_nickname');
    final value_dart = prefs.getBool('key_dart');
}

3、写入方法如：

void saveInfo(String value_nickname) async{
    final SharedPreferences prefs = await _prefs;
    prefs.setString('key_nickname', value_nickname);
    prefs.setBool('key_dart',  this.value_dart);
}

4、完整代码如下：

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';

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

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

  @override
  Widget build(BuildContext context) {
    return Container(
      child: MaterialApp(
        title: 'shared_preferences本地存储',
        debugShowCheckedModeBanner: false,
        home: FirstPage(),
      ),
    );
  }
}

class FirstPage extends StatefulWidget{
  FirstPage({Key key}) : super(key:key);

  _FirstPageState createState() => _FirstPageState();
}

class _FirstPageState extends State<FirstPage>{
  //实例化SharedPreferences，是异步处理
  Future<SharedPreferences> _prefs = SharedPreferences.getInstance();

  var controller = TextEditingController();
  bool value_dart = false;
  bool value_js = false;
  bool value_java = false;

  @override
  void initState() {
    super.initState();
    //从缓存中取出数据
    initFromCache();
  }

  //从缓存中取值
  void initFromCache() async{
    final SharedPreferences prefs = await _prefs;
    final value_nickname = prefs.getString('key_nickname');
    final value_dart = prefs.getBool('key_dart');
    final value_js = prefs.getBool('key_js');
    final value_java = prefs.getBool('key_java');
    setState(() {
      controller.text = (value_nickname==null ? '' : value_nickname);
      this.value_dart = (value_dart==null ? false : value_dart);
      this.value_js = (value_js==null ? false : value_js);
      this.value_java = (value_java==null ? false : value_java);
    });
  }

  //将值存储到缓存
  void saveInfo(String value_nickname) async{
    final SharedPreferences prefs = await _prefs;
    prefs.setString('key_nickname', value_nickname);
    prefs.setBool('key_dart',  this.value_dart);
    prefs.setBool('key_js', this.value_js);
    prefs.setBool('key_java', this.value_java);
  }

  @override
  Widget build(BuildContext context) {
   return Scaffold(
     appBar: AppBar(
       title: Text('SharedPreferences示例'),
     ),
     body: Container(
       padding: EdgeInsets.all(10.0),
       child: Column(
         crossAxisAlignment: CrossAxisAlignment.center,
         children: [
           TextField(
             controller: controller,
             decoration: InputDecoration(
               labelText: '昵称',
               hintText: '请输入昵称'
             ),
           ),
           Text('你喜欢的编程语言'),
           Row(
             mainAxisAlignment: MainAxisAlignment.center,
             children: [
               Text('Dart'),
               Switch(
                 value: value_dart,
                 onChanged: (isChanged){
                   setState(() {
                     this.value_dart = isChanged;
                   });
               })
             ],
           ),
           Row(
             mainAxisAlignment: MainAxisAlignment.center,
             children: [
               Text('Javascript'),
               Switch(
                 value: value_js,
                 onChanged: (isChanged){
                   setState(() {
                     this.value_js = isChanged;
                   });
               })
             ],
           ),
           Row(
             mainAxisAlignment: MainAxisAlignment.center,
             children: [
               Text('Java'),
               Switch(
                 value: value_java,
                 onChanged: (isChanged){
                   setState(() {
                     this.value_java = isChanged;
                   });
               })
             ],
           ),
           MaterialButton(
             child: Text('保存'),
             onPressed: (){
               this.saveInfo(controller.text);
             },
           )
         ],
       ),
     ),
   );
  }
}

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