c# 单例模式传参且线程安全

Question

1.用c#构建数据库访问类
2.采用单例模式，要求能传参且是在线程安全模式下访问

Answer 1

之前这样写的

        private string ConnectionString = string.Empty;
        private static DapperHelper instance;
        public static DapperHelper Instance
        {
            get
            {
                if(instance == null)
                {
                    lock(instanceObj)
                    {
                        if(instance == null)
                        {
                            instance = new DapperHelper();
                        }
                    }
                }
                return instance;
            }
        }
        #endregion

        public DapperHelper()
        {
            ConnectionString = GetConnectionString();
        }


        public MySqlConnection MySQLConnection(string connstring)
        {
            using(this.mysqlDBConn = new MySqlConnection(connstring))
            {
                return this.mysqlDBConn;
            }
        }

        public string GetConnectionString(string ip = "127.0.0.1")
        {
            ConfigurationBuilder configuration = new ConfigurationBuilder();
            string assemblyFilePath = Assembly.GetExecutingAssembly().Location;
            string assemblyDirPath = Path.GetDirectoryName(assemblyFilePath);

            var config = configuration.SetBasePath(assemblyDirPath).AddJsonFile(file =>
            {
                file.Path = "/appsettings.json";
                file.Optional = false;
                file.ReloadOnChange = true;
            }).Build();
            return string.Format(config.GetConnectionString("mssql"), ip);            
        }