Flutter中的几种本地持久化存储

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APP中的持久化数据存储是不可或缺的功能，本文主要介绍下Flutter中里面的几种持久化存储：

shared_preferences

安卓端，基于SharePreferences；iOS端基于NSUserDefaults开发 用于简单key-value形式存储

1. 引入

dependencies:
  shared_preferences: ^2.0.8
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2. 基本用法：

class LocalStorage {
  static SharedPreferences? prefs;

  static initSP() async {
    prefs = await SharedPreferences.getInstance();
  }

  static save(String key, String value) {
    prefs?.setString(key, value);
  }

  static get(String key) {
    return prefs?.get(key);
  }

  static remove(String key) {
    prefs?.remove(key);
  }
}
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path_provider

文件存储

1. 引入

dependencies:
    path_provider: ^2.0.7
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2. 基本介绍

• 获取应用缓存目录: getTemporaryDirectory

  • 类似iOS的NSTemporaryDirectory和Android的getCacheDir
  • /data/user/0/包名/cache

• 获取应用文件目录: getApplicationDocumentsDirectory

  • 类似iOS的NSDocumentDirectory和Android上的AppData目录
  • 应用程序被删除时，系统会清除目录
  • /data/user/0/包名/app_flutter

• 存储卡: getExternalStorageDirectory

  • 仅支持Android平台
  • /storage/emulated/0/Android/data/包名/files

3. 基本用法

/// 拿到存储路径

Future<String> getTemporaryDirectoryString()async{
  final directory = await getTemporaryDirectory();
  return directory.path;
}

Future<String> getApplicationDocumentsDirectoryString()async{
  final directory = await getApplicationDocumentsDirectory();
  return directory.path;
}

Future<String> getExternalStorageDirectoryString()async{
  final directory =  await getExternalStorageDirectory();
  return directory?.path ?? "";
}

// 创建对文件位置的引用
  Future<File> get _localFile async {
    final path = await getApplicationDocumentsDirectoryString();
    return new File('$path/counter.txt');
  }

// 将数据写入文件
  Future<File> writeCounter(int counter) async {
    final file = await _localFile;
    // Write the file
    return file.writeAsString('$counter');
  }

// 从文件中读取数据
  Future<int> readCounter() async {
    try {
      final file = await _localFile;
      // Read the file
      String contents = await file.readAsString();

      return int.parse(contents);
    } catch (e) {
      // If we encounter an error, return 0
      return 0;
    }
  }


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sqflite数据库

1. 引入

dependencies:
  sqflite: ^2.0.0+4
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2.基本介绍

• 执行sq语句，创建表
• 提供获取Transaction的方法
• 使用Transaction执行增删改查的sq语句

3. 基本使用

class MainDatabaseManager {
  // 工厂模式
  factory MainDatabaseManager() => _getInstance();
  static MainDatabaseManager get instance => _getInstance();
  static MainDatabaseManager? _instance;
  static Database? tkDatabase;
  static List<String> _nameList = [];

  MainDatabaseManager._internal() {
    // 初始化
  }
  static MainDatabaseManager _getInstance() {
    if (_instance == null) {
      _instance = new MainDatabaseManager._internal();
    }
    _instance!._createTable();
    return _instance!;
  }

  ///初始化数据库
  initDB() {
    _createTable();
  }

  ///打开数据库,创建数据缓存表
  _createTable() async {
    var databasePath = await getDatabasesPath();
    String path = join(databasePath, "tkDataBase.db");

    ///打开数据库
    tkDatabase = await openDatabase(path, version: 1,
        onCreate: (Database db, int version) async {
      /// 创建表
      await db.execute(
          "create table if not EXISTS TK_Main_Data (id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,name TEXT UNIQUE,data BLOB)");
    });
  }

  ///操作事务Transaction
  commitTransaction(Function(Transaction txn) action) async {
    try {
      await tkDatabase?.transaction((txn) async {
        Batch batch = txn.batch();
        await action(txn);
        await batch.commit(noResult: true, continueOnError: true);
      });
    } catch (e) {
      print('--- transaction failed -----');
    }
  }

  /*
     保存到数据库,区分当前用
     - parameter name: 保存的名称（用于查询）
     - parameter data: 数据
     - parameter type: 类型
     */
  _saveDataWith(
      String name, bool containsMember, String data, Transaction txn) async {
    String dataName = name + (containsMember ? UserStore().getMemberId() : "");
    int id = await txn.rawInsert(
        'INSERT or replace INTO TK_Main_Data(name,data) VALUES(?,?)',
        [dataName, data]);
    print('inserted2:$id');
  }

  ///更新数据
  updateData(
      String name, bool containsMember, dynamic data, Transaction txn) async {
    dynamic result = await selectData(name, containsMember, txn);
    if (result == null || result == "") {
      _nameList.add(name);
    }
    _saveDataWith(name, containsMember, data, txn);
  }

  /*
     查询数据

     - parameter name: 要查询的数据的名称
     - parameter type: 类型
     - returns: 返回的数据
     */
  Future<dynamic> selectData(
      String name, bool containsMember, Transaction txn) async {
    String dataName = name + (containsMember ? UserStore().getMemberId() : "");

    /// 查询
    dynamic result = await txn
        .rawQuery("select data from TK_Main_Data where name = '$dataName'");
    if (result != null && result is List && result.length > 0) {
      return result.first["data"] ?? "";
    }
    return "";
  }

  ///退出登录时,删除与当前用户有关的缓存
  deleteAllDataForMember(Transaction txn) async {
    if (UserStore.instance.getMemberId() != "") {
      for (String name in _nameList) {
        String dataName =
            name + UserStore.instance.getMemberId(); //与当前用户有关的,无关的不需要删除
        await txn
            .execute("delete from TK_Main_Data where name = (?)", [dataName]);
      }
      _nameList = [];
    }
  }

  onDisposed() {
    tkDatabase?.close();
  }
}
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