對象引用不設置到對象的實例 - OracleDataReader

Question

試圖返回使用OracleDataReader數據，讓

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

任何人都可以提出什麼我缺少/做錯了？

感謝

牛逼

  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

您將ocmd聲明爲null，但隨後您又創建了另一個OracleCommand對象作爲cmd。 ocmd從未實例化。

這部分是錯誤的：

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

它應該是：

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

Answer 2

ocmd和cmd是兩個不同的變量。

Answer 3

OracleCommand cmd = new OracleCommand(mysql, cn); 

應該

OracleCommand ocmd = new OracleCommand(mysql, cn);