非常不错的三种存储，能够持久化存储和读取，指定路径后可以实现即使App卸载了一样数据还存储在用户的设备内，下次下载依然读取原数据，使用起来非常方便。

使用示例

setUserName() async{
    SharedPreferences prefs = await SharedPreferences.getInstance();
    prefs.setString(mUserName,"小明");
}

getUserName() async{
    SharedPreferences prefs = await SharedPreferences.getInstance();
    userName = prefs.getString(mUserName);
}

displayUserName() {
    Future<String> userName = getUserName();
    userName.then((String userName) {
           Scaffold.of(context).showSnackBar(
                    SnackBar(content: Text("数据获取成功：$userName")));
    });
}

// 找到正确的本地路径
Future<String> get _localPath async {
  final directory = await getApplicationDocumentsDirectory();
  return directory.path;
}

// 创建对文件位置的引用
Future<File> get _localFile async {
  final path = await _localPath;
  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;
  }
}

// 获取数据库文件的存储路径
var databasesPath = await getDatabasesPath();
String path = join(databasesPath, 'demo.db');

// 创建数据库表
db = await openDatabase(path, version: 1,
       onCreate: (Database db, int version) async {
   await db.execute('''
        CREATE TABLE $tableBook (
            $columnId INTEGER PRIMARY KEY, 
            $columnName TEXT, 
            $columnAuthor TEXT, 
            $columnPrice REAL, 
            $columnPublishingHouse TEXT)
          ''');
    });

// 插入数据
Future<int> rawInsert(String sql, [List<dynamic> arguments]);

Future<int> insert(String table, Map<String, dynamic> values,
      {String nullColumnHack, ConflictAlgorithm conflictAlgorithm});


// 查询数据
Future<List<Map<String, dynamic>>> rawQuery(String sql,
      [List<dynamic> arguments]);

Future<List<Map<String, dynamic>>> query(String table,
      {bool distinct,
      List<String> columns,
      String where,
      List<dynamic> whereArgs,
      String groupBy,
      String having,
      String orderBy,
      int limit,
      int offset});

// 更新数据
Future<int> rawUpdate(String sql, [List<dynamic> arguments]);

Future<int> update(String table, Map<String, dynamic> values,
      {String where,
      List<dynamic> whereArgs,
      ConflictAlgorithm conflictAlgorithm});

// 删除
Future<int> rawDelete(String sql, [List<dynamic> arguments]);

Future<int> delete(String table, {String where, List<dynamic> whereArgs});

// 关闭数据库
Future close() async => db.close();

参考学习相关文章：

Flutter 构建完整应用手册-持久化

Flutter数据存储之shared_preferences

Flutter中的本地存储