ios开发Flutter之数据存储

void _incrementCounter() {
  //创建对象，用于操作存储和读取。
  SharedPreferences.getInstance().then((SharedPreferences prefs) {
    setState(() {
      _counter++;
    });
    prefs.setInt('counter', _counter);
  });
  }

 SharedPreferences.getInstance().then((SharedPreferences prefs) {
      setState(() {
        _counter = prefs.getInt('counter') ?? 0;
      });
    });

 late Database _db;
  @override
  void initState() {
    super.initState();
    _initDatabase().then((value) => _db = value);
  }
  Future<Database> _initDatabase() async {
    Database db = await getDatabasesPath()
        .then((value) => join(value, 'test_db.db'))
        .then((value) => openDatabase(value, version: 1,
                onCreate: (Database db, int version) async {
              // 建表
              await db.execute(
                  'CREATE TABLE LK_Text(id INTEGER PRIMARY KEY,name TEXT, age INT)');
            }));
    return db;
  }

    _db.transaction((txn) async {
      txn
          .rawInsert('INSERT INTO LK_Text(name,age) VALUES("zhangsan",16)')
          .then((value) => print(value));
      txn
          .rawInsert('INSERT INTO LK_Text(name,age) VALUES("lisi",17)')
          .then((value) => print(value));
    });

_db.rawQuery('SELECT * FROM LK_Text').then((value) => print(value));

_db.rawUpdate('UPDATE LK_TEXT SET age = 18 WHERE age = 16');

  _db
        .rawQuery('SELECT * FROM LK_Text')
        .then((value) => print(value))
        .then((value) {
      // 删除表
      _db.delete('LK_Text').then((value) => _db.close());
    });

    // 删除数据库
    getDatabasesPath()
        .then((value) => join(value, 'test_db.db'))
        .then((value) => deleteDatabase(value));