Question

When using a Stored procedure on SQL 2008 and C# 4.0, I am unable to retrieve OUTPUT information and return info from a Select statement. I keep getting “Object reference not set to an instance of an object.”. When i do ExecuteScalar() i get the rows, but not the data. Found a few examples out there and they look like what i’m doing, so i think i’m missing something simple in front of me. Thanks.

Stored procedure

USE [PhoneDb]
GO
/****** Object:  StoredProcedure [dbo].[TestPagingProcedure]    Script Date: 06/16/2011 08:39:03 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

ALTER PROCEDURE [dbo].[TestPagingProcedure] 
    -- Add the parameters for the stored procedure here
    @startRowIndex int,
    @maximumRows int,
    @totalRows int OUTPUT


AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

DECLARE @first_id UNIQUEIDENTIFIER
DECLARE @startRow int

SET @startRowIndex =  (@startRowIndex - 1)  * @maximumRows

IF @startRowIndex = 0 
SET @startRowIndex = 1

SET ROWCOUNT @startRowIndex

SELECT @first_id = ExtensionGUID FROM ExtItem ORDER BY ExtensionGUID

PRINT @first_id

SET ROWCOUNT @maximumRows

SELECT 
ExtensionGUID, AesExt, AesHashPassword, ToNumber, AgentExt, Name, JpgImageName, BigImageName, WbmpImageName
 FROM ExtItem WHERE 
ExtensionGUID >= @first_id 
ORDER BY ExtensionGUID

SET ROWCOUNT 0

-- GEt the total rows 

SELECT @totalRows = COUNT(ExtensionGUID) FROM ExtItem

END

C# Code

 public bool GetPagedResults(string startRowIndex, string maxRows, ref double totalRowsReturned)
    {
        bool IsSuccess = false;
        string clearPassword = "";
        Log.WriteLine("GetExtList : ENTERED GETEXTITEM: ", Log.DEBUG_LEVEL.VERBOSE);
        SqlConnection MyConnection = null;
        EnDecrypt hasher = null;

        try
        {
            if (SQLLookup.DatabaseString == "")
            {
                Log.WriteLine("GetPagedResults : SQLLookup.DatabaseString is empty:", Log.DEBUG_LEVEL.VERBOSE);
                SQLLookup.SQLFinder();
                Log.WriteLine("GetPagedResults : SQL FINDER RUN: SQLLookup.DatabaseString:'" + SQLLookup.DatabaseString + "'", Log.DEBUG_LEVEL.VERBOSE);
            }

            Log.WriteLine("GetPagedResults: SQL Server '" + SQLLookup.DatabaseString + "'", Log.DEBUG_LEVEL.VERBOSE);

            _extItemList.Clear();  // Keep new records from just being appended to existing list.

            hasher = new EnDecrypt("SetMyKey", "SaltGenerator");

            // Create a Connection to SQL Server
            MyConnection = new SqlConnection(@"Data Source= " + SQLLookup.DatabaseString + @"; Initial Catalog=PhoneDb;Integrated Security=True");

            SqlCommand myCommand = new SqlCommand("TestPagingProcedure", MyConnection);
            myCommand.CommandType = CommandType.StoredProcedure;

            /* ASSIGN PARAMETERS */
            myCommand.Parameters.Add(new SqlParameter("@startRowIndex", startRowIndex));
            myCommand.Parameters.Add(new SqlParameter("@maximumRows", maxRows));
            myCommand.Parameters.Add("@totalRows", SqlDbType.Int, 4);
            myCommand.Parameters["@totalRows"].Direction = ParameterDirection.Output;


            Log.WriteLine("GetPagedResults:3 After try ", Log.DEBUG_LEVEL.VERBOSE);
            Log.WriteLine("GetPagedResults:3 startRowIndex = " + startRowIndex + "  maxRows = " + maxRows, Log.DEBUG_LEVEL.VERBOSE);
            MyConnection.Open();
            SqlDataReader Reader = myCommand.ExecuteReader();

            Log.WriteLine("GetPagedResults  BEFORE WHILE LOOP", Log.DEBUG_LEVEL.VERBOSE);
            while (Reader.Read())
            {
                /* BUILD EXT ITEM*/
                ExtItem extItem = new ExtItem();
                if (Reader.IsDBNull(0) || Reader.GetGuid(0) == Guid.Empty)
                    extItem.ExtensionGUID = Guid.Empty;
                else
                    extItem.ExtensionGUID = Reader.GetGuid(0);

                if (Reader.IsDBNull(1) || Reader.GetString(1) == "")
                    extItem.AesExt = "No value";
                else
                    extItem.AesExt = Reader.GetString(1);


                /* ADD ITEM TO LIST */
                AddItem(extItem);

                //Log.WriteLine("GetExtList extItem: " + extItem.ToString(), Log.DEBUG_LEVEL.VERBOSE);
            }

            // get the total rows 
            Log.WriteLine("GetPagedResults: New Total number of pages: " + (int)myCommand.Parameters[2].Value, Log.DEBUG_LEVEL.TERSE);
            // totalRowsReturned = myCommand.Parameters["@totalRows"];

            IsSuccess = true;

            MyConnection.Close();
            Log.WriteLine("GetPagedResults: RETURNING:", Log.DEBUG_LEVEL.VERBOSE);
        }

        catch (Exception ex)
        {
            Log.WriteLine("GetPagedResults: Unable to retrieve Extension list. Caught Exception " + ex.Message,
                Log.DEBUG_LEVEL.TERSE);
            IsSuccess = false;
        }

        MyConnection.Close();

        return IsSuccess;
    }

Answer 1

According to, http://msdn.microsoft.com/en-us/library/ms971497, you must close the datareader before you process the output parameters.