sqldatareader错误“关闭阅读器时，无效的调用Read的尝试." [英] sqldatareader error "Invalid attempt to call Read when reader is closed."

问题描述

你好，
当我从sqldatareader读取数据时，出现错误关闭阅读器时，无效的尝试调用Read的尝试."
我的代码是

Hello there,
when I am reading data from sqldatareader I am getting error "Invalid attempt to call Read when reader is closed."
My code is

string cid = "a";

            string s = "select Student_Id from tbstudent_batchmaster where Batch_Identity='" + batchid + "'";

            ClsConnection.Conn.Close();
            ClsConnection.Conn.Open();

            SqlCommand cmd = new SqlCommand(s, ClsConnection.Conn);

            SqlDataReader sdr = cmd.ExecuteReader();
            while (sdr.Read())
            {

                cid = sdr.GetValue(0).ToString();
                
                Int32.TryParse(cid, out  actval);
               // fillstudentdata();

                ClsConnection.Conn.Close();
                ClsConnection.Conn.Open();

                dtstudent.ColumnHeadersVisible = true;
                dtstudent.RowHeadersVisible = false;
                dtstudent.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.Fill;
                string selectCommand1 = "select  FName+' '+LName as Name from ADD_Master where ADD_No='" + actval + "'";
                SqlDataAdapter sqlDataAdapter1 = new SqlDataAdapter(selectCommand1, ClsConnection.Conn);
                SqlCommand cmd1 = new SqlCommand();

                cmd1.CommandText = selectCommand1;
                DataSet ds1 = new DataSet();
                sqlDataAdapter1.Fill(ds1);
                ClsConnection.Conn.Close();
                dtstudent.DataSource = ds1.Tables[0];
                DataGridViewCheckBoxColumn cb = new DataGridViewCheckBoxColumn();
                cb.HeaderText = "test";
                cb.Name = "test";
                cb.Visible = true;
                cb.Width = 40;
                dtstudent.Columns.Add(cb);
                dtstudent.Columns[0].Visible = false;
                dtstudent.SelectionMode = DataGridViewSelectionMode.FullRowSelect;
                dtstudent.Refresh();
                

            }
           

            ClsConnection.Conn.Close();
        }

有谁可以帮忙????请.

can any one help ???? please.

推荐答案

不要玩任何连接. Reader将为您打开和关闭连接.完成后关闭阅读器-使用``using''语句自动完成阅读器

Don''t play with connection at all. Reader will open and close the connection for you. Close the reader when finish - use ''using'' statement to do it automatically

尝试删除所有打开和关闭的控件，并在while循环之前仅打开一个控件，并只关闭一个控件在您的while循环之后，看看是否有帮助...

try removing all open and close and have just one open before your while loop and have only one close after your while loop, and see if that helps...

我认为Catalin Serafimescu希望您这样进行操作:

I think Catalin Serafimescu wants you to do things this way:

SqlConnection connection = new SqlConnection(connectionString);
using(connection) // will make certain that the connection is properly disposed
{
 connection.Open();
 SqlCommand command = connection.CreateCommand();
 using(command) // will make certain that the command is properly disposed
 {
  command.CommandText = sqlStatement;
  SqlDataReader dataReader = command.ExecuteReader();
  using(dataReader) // will make certain that the reader is properly disposed
  {
   while(dataReader.Read())
   {
     // process records. don''t close and open the connection
   }
  }
 }
}

最好的问候
Espen Harlinn

Best regards
Espen Harlinn

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