基于shared_preferences本地存储操作

• shared_preferences 是什么？
• 如何使用shared_preferences？
• shared_preferences有那些常用的API？
• 基于shared_preferences实现计数器Demo

数据存储是开发APP必不可少的一部分，比如页面缓存，从网络上获取数据的本地持久化等，那么在Flutter中如何进行数据存储呢？

Flutter官方推荐我们用sharedpreferences进行数据存储，类似于RN中的AsyncStorage。

什么是shared_preferences?

shared_preferences是Flutter社区开发的一个本地数据存取插件：

• 简单的，异步的，持久化的key-value存储系统；
• 在Android上它是基于SharedPreferences的；
• 在iOS上它是基于NSUserDefaults的；

如何使用shared_preferences？

首先在pubspec.yaml文件中添加：

dependencies:
  shared_preferences: ^0.5.1+

记得运行安装哦：flutter packages get

在需要用到的文件中导入：

import 'package:shared_preferences/shared_preferences.dart';

存储数据

final prefs = await SharedPreferences.getInstance();

// set value
prefs.setInt('counter', counter);

读取数据

final prefs = await SharedPreferences.getInstance();

// Try reading data from the counter key. If it does not exist, return 0.
final counter = prefs.getInt('counter') ?? 0;}

删除数据

final prefs = await SharedPreferences.getInstance();
prefs.remove('counter');

shared_preferences有那些常用的API？

存储相关

如上图shared_preferences支持int, double, bool, string 与 stringList类型的数据存储；

读取相关

上图shared_preferences中所提供的读取相关的API；

基于shared_preferences实现计数器Demo

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

void main() {
  runApp(MaterialApp(
    home: Scaffold(
      appBar: AppBar(
        title: Text('shared_preferences'),
      ),
      body: _CounterWidget(),
    ),
  ));
}

class _CounterWidget extends StatefulWidget {
  @override
  _CounterState createState() => _CounterState();
}

class _CounterState extends State<_CounterWidget> {
  String countString = '';
  String localCount = '';

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Column(
        children: <Widget>[
          RaisedButton(
              onPressed: _incrementCounter, child: Text('Increment Counter')),
          RaisedButton(onPressed: _getCounter, child: Text('Get Counter')),
          Text(
            countString,
            style: TextStyle(fontSize: 20),
          ),
          Text(
            'result：' + localCount,
            style: TextStyle(fontSize: 20),
          ),
        ],
      ),
    );
  }

  _incrementCounter() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    setState(() {
      countString = countString + " 1";
    });
    int counter = (prefs.getInt('counter') ?? 0) + 1;
    await prefs.setInt('counter', counter);
  }

  _getCounter() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    setState(() {
      localCount = prefs.getInt('counter').toString();
    });
  }
}

参考

• Storing key-value data on disk

 

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

class TestSharePreferences extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    // TODO: implement createState
    return _TestSharePreferencesState();
  }
}

class _TestSharePreferencesState extends State<TestSharePreferences> {
  String strInput = '';
  String strLocal = '';
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return Column(
      children: [
        Container(
          width: double.infinity,
        ),
        Row(
          // mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Container(
              width: 250,
              child: TextField(
                style: TextStyle(color: Colors.black87),
                decoration: InputDecoration(hintText: "输入要保存的数据"),
                onChanged: (str) {
                  strInput = str;
                  print('str: $strInput');
                },
              ),
            ),
            Padding(
              padding: EdgeInsets.only(left: 20),
              child: OutlineButton(
                onPressed: () async {
                  SharedPreferences sharePreferences =
                      await SharedPreferences.getInstance();
                  sharePreferences.setString('strLocal', strInput);
                },
                child: Text("保存"),
              ),
            )
          ],
        ),
        Row(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Container(
              width: 250,
              child: Text("strLocal: $strLocal"),
            ),
            Padding(
              padding: EdgeInsets.only(left: 20),
              child: OutlineButton(
                onPressed: () async {
                  SharedPreferences sharePreferences =
                      await SharedPreferences.getInstance();
                  String message = sharePreferences.getString('strLocal') ?? '';
                  setState(() {
                    strLocal = message;
                  });
                },
                child: Text("读取"),
              ),
            )
          ],
        ),
      ],
    );
  }

}