c# - 对象引用未设置为对象的实例 - OracleDataReader

Question

尝试使用OracleDataReader，获取 返回数据

"Object reference not set to an instance of an object " at the line "odr = 
ocmd.ExecuteReader();",

谁能建议我错过/做错了什么？

谢谢

吨

           OracleConnection cn = null;
            OracleDataReader odr = null;
            OracleCommand ocmd = null;

            String con1 = System.Configuration.ConfigurationManager.ConnectionStrings["HousingDBConnectionString"].ConnectionString;
            cn = new OracleConnection(con1);
            cn.Open();

            string mysql = "SELECT stuff from tables";
            OracleCommand cmd = new OracleCommand(mysql, cn);
            odr = ocmd.ExecuteReader();
            Label2.Text = "connection success";

            ListBox1.Items.Clear();
            while (odr.Read()) 
            {
                ListBox1.Items.Add(odr["TCY_CORRESPOND_NAME"].ToString());
            }

Answer 1

ocmdcmd是两个不同的变量。

Answer 2

您将 ocmd 声明为 null，但随后您将另一个 OracleCommand 对象创建为 cmd。ocmd 从未实例化。

这部分是错误的：

OracleCommand cmd = new OracleCommand(mysql, cn); 
odr = ocmd.ExecuteReader(); 

它应该是：

OracleCommand cmd = new OracleCommand(mysql, cn); 
odr = cmd.ExecuteReader(); 

Answer 3

OracleCommand cmd = new OracleCommand(mysql, cn);

应该

OracleCommand ocmd = new OracleCommand(mysql, cn);