MySql.Data.Client中无法识别Execute Reader

Question

我正在创建跨平台应用程序，并且在用于数据库连接的类中，执行reader，scalar，conn.open（），conn.close（）和其他人无法识别。我收到错误，说明在系统中定义的“引用类型'组件”声明，但它没有找到“。我已经下载了MySql.Data nuget并添加了MySql的所有引用需求，我不知道是什么导致这个问题。请帮忙。

using System.Collections.Generic;
using System;
using System.Data;
using MySql.Data.MySqlClient;


namespace Camera
{
     public class DBConn
    {
        private static MySqlConnection getDBConn()
        {
        string testDB;
        //connection string with database location
        //change the database location in following line
        testDB = "Server = myip; Port = myport; database = readingmeterdb; User Id = root; Password = mypassword; charset = utf8";

        return new MySqlConnection(testDB);
    }

    public static List<machines> getmachine()
    {
        List<machines> machinelist = new List<machines>();
        MySqlConnection mydbconn = getDBConn();
        string qry = "SELECT * FROM machines";
        MySqlCommand cmd = new MySqlCommand(qry, mydbconn);

        try
        {
            mydbconn.Open();
            MySqlDataReader myrdr = cmd.ExecuteReader();
            while (myrdr.Read())
            {
                machines machine = new machines(int.Parse(myrdr["machineId"].ToString()), myrdr["machineDesc"].ToString());
                machinelist.Add(machine);
            }
            return machinelist;
        }
        catch (Exception ex)
        {

            return null;
        }

        finally {
            mydbconn.Close();
        }
    }


}

}