SharedPreferences 存储
缓存大量的键值对信息（比方记录用户是否浏览了布告，或是简略的计数），能够应用 SharedPreferences。
SharedPreferences 会以原生平台相干的机制，为简略的键值对数据提供长久化存储，即在 iOS 上应用 NSUserDefaults，在 Android 应用 SharedPreferences。
SharedPreferences 的应用形式非常简单不便。不过须要留神的是，以键值对的形式只能存储根本类型的数据，比方 int、double、bool 和 string。
1. pubspec.yaml引入
shared_preferences: 0.5.12+4
2. 代码
import 'dart:developer';import 'package:flutter/material.dart';import 'package:shared_preferences/shared_preferences.dart';void main() { runApp(MyApp());}class MyApp extends StatelessWidget { // This widget is the root of your application. @override Widget build(BuildContext context) { return MaterialApp( title: 'Flutter Demo', theme: ThemeData( primarySwatch: Colors.blue, ), home: MyHomePage(title: 'Flutter Demo Home Page'), ); }}class MyHomePage extends StatefulWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; @override _MyHomePageState createState() => _MyHomePageState();}class _MyHomePageState extends State<MyHomePage> { int _counter = 0;//波及到耗时的文件读写，以异步的形式对这些操作进行包装//读取SharedPreferences中key为counter的值 Future<int> _loadCounter() async { SharedPreferences prefs = await SharedPreferences.getInstance(); int counter = (prefs.getInt('counter') ?? 0); return counter; }//递增写入SharedPreferences中key为counter的值 Future<void> _incrementCounter() async { SharedPreferences prefs = await SharedPreferences.getInstance(); int counter = (prefs.getInt('counter') ?? 0) + 1; print("以后值: " + counter.toString()); prefs.setInt('counter', counter); //setter（setInt）办法会同步更新内存中的键值对，而后将数据保留至磁盘，因而无需再调用更新办法强制刷新缓存 } _fresh() { // _incrementCounter(); _incrementCounter().then((_) => { _loadCounter().then((value) { setState(() { _counter = value; }); print("before:$value"); }) }); } // void _incrementCounter() { // setState(() { // _counter++; // }); // } @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( // Here we take the value from the MyHomePage object that was created by // the App.build method, and use it to set our appbar title. title: Text(widget.title), ), body: Center( // Center is a layout widget. It takes a single child and positions it // in the middle of the parent. child: Column( mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[ Text( 'You have pushed the button this many times:', ), Text( '$_counter', style: Theme.of(context).textTheme.headline4, ), ], ), ), floatingActionButton: FloatingActionButton( onPressed: _fresh, tooltip: 'Increment', child: Icon(Icons.add), ), // This trailing comma makes auto-formatting nicer for build methods. ); }}数据库存储
如果须要长久化大量格式化后的数据，并且这些数据还会以较高的频率更新，为了思考进一步的扩展性，通常会选用 sqlite 数据库来应答这样的场景。
与文件和 SharedPreferences 相比，数据库在数据读写上能够提供更快、更灵便的解决方案。
1. pubspec.yaml引入
sqflite: 1.3.2+1 path_provider: ^1.6.24 2.代码
import 'package:flutter/material.dart';import 'package:sqflite/sqflite.dart';import 'package:path/path.dart';import 'package:path_provider/path_provider.dart';import 'dart:io';void main() { runApp(MyApp());}class MyApp extends StatelessWidget { // This widget is the root of your application. @override Widget build(BuildContext context) { return MaterialApp( title: 'Flutter Demo', theme: ThemeData( primarySwatch: Colors.blue, ), home: MyHomePage(title: 'Flutter Demo Home Page'), ); }}class MyHomePage extends StatefulWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; @override _MyHomePageState createState() => _MyHomePageState();}class Student { String id; String name; int score; //构造方法 Student({ this.id, this.name, this.score, }); //用于将JSON字典转换成类对象的工厂类办法 factory Student.fromJson(Map<String, dynamic> parsedJson) { return Student( id: parsedJson['id'], name: parsedJson['name'], score: parsedJson['score'], ); } Map<String, dynamic> toJson() { return { 'id': id, 'name': name, 'score': score, }; }}class _MyHomePageState extends State<MyHomePage> { var student1 = Student(id: '123', name: '张三', score: 110); query_database(id) { Future<Student> user = query_by_id(id); user.then((t) { print("单用户查问胜利"); print('the sroce is : ' + t.score.toString()); student1.score = t.score; }); } //插入数据 Future<void> insertStudent(Student std) async { final Database db = await database; await db.insert( 'students', std.toJson(), //插入抵触策略，新的替换旧的 conflictAlgorithm: ConflictAlgorithm.replace, ); } Future<Student> query_by_id(String id) async { final Database db = await database; List<Map> maps = await db.query('students', columns: ['id', 'name', 'score'], where: 'id = ?', whereArgs: [id]); if (maps.length > 0) { print("依据id查到了数据"); return Student.fromJson(maps.first); } print("依据id没有查到数据"); return null; } //初始化数据库办法 initDB() async { Directory documentsDirectory = await getApplicationDocumentsDirectory(); String path = join(documentsDirectory.path, "students_database.db"); return await openDatabase(path, version: 1, onOpen: (db) {}, onCreate: (Database db, int version) async { await db.execute(''' CREATE TABLE students(id TEXT PRIMARY KEY, name TEXT, score INTEGER) '''); }); } Database _database; Future<Database> get database async { if (_database != null) { print(_database); return _database; } _database = await initDB(); print("创立新数据库"); return _database; } void _incrementCounter() async { student1.score += 1; await insertStudent(student1); setState(() {}); } Future<List<Student>> students() async { final Database db = await database; final List<Map<String, dynamic>> maps = await db.query('students'); return List.generate(maps.length, (i) => Student.fromJson(maps[i])); } @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text(widget.title), ), body: Center( child: Column( mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[ Text( 'You have pushed the button this many times:', ), Text( student1.score.toString(), style: Theme.of(context).textTheme.headline4, ), ], ), ), floatingActionButton: FloatingActionButton( onPressed: _incrementCounter, tooltip: 'Increment', child: Icon(Icons.add), ), ); } @override void dispose() async { // TODO: implement dispose super.dispose(); final Database db = await database; db.close(); }}Flutter 写的app, 须要源码能够私信~~
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