Retrieving VarChar(MAX) from SQL Server using C# and a stored procedure

Question

I have a WebMethod which is called to retrieve a varchar(max) column from SQL Server. I create my neccessary stored procedure, which works fine in Management Studio, but when I run the below code I get an error:

Invalid attempt to read when no data is present

Code:

[WebMethod]
public static void PopulatePopUp(string arg)
{
    var str = GlobalStatic.ExceptBlanks(arg);

    SqlConnection conn = new SqlConnection(WebConfigurationManager.ConnectionStrings["Conn"].ConnectionString);

    SqlDataReader rdr = null;

    using (conn)
    {
        using (SqlCommand cmd = new SqlCommand())
        {
            conn.Open();

            cmd.CommandText = "GetMessage_Sel";
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.Parameters.Add("@messageId", SqlDbType.VarChar, -1).Value = str;
            cmd.Parameters.Add("@RowCount", SqlDbType.Int).Direction = ParameterDirection.Output;

            cmd.Connection = conn;

            try
            {
                rdr = cmd.ExecuteReader();

                if (rdr.HasRows)
                {
                    string fieldValue = rdr.GetString(0);
                }
                else
                {
                    Console.WriteLine("No rows found.");
                }

                rdr.Close();
            }
            catch (Exception err)
            {
                // handle the error
                //messageInsert = false;
            }
            finally
            { 
                conn.Close(); 
            }
        }
    }
}

Answer 1

try this

                    if (rdr.HasRows)
                    {
                        while(rdr.Read())
                        {
                            string fieldValue = rdr[0].ToString();
                        }

                    }
                    else
                    {
                        Console.WriteLine("No rows found.");
                    }