System.NullRefe renceException - Object reference not set to an instance of an object

[Rodusa]

I am getting this exception error which is driving me nuts.
System.NullRefe renceException - Object reference not set to an instance
of an object

If I comment this line, I don't get any errors:
string Total_Dollar_Am ount = GetTotal(sql,"t est");

namespace SalesReport
{
/// <summary>
/// Summary description for SalesReport.
/// </summary>
public class SalesReport : System.Web.UI.P age
{
protected System.Web.UI.W ebControls.Butt on Button1;

private void Page_Load(objec t sender, System.EventArg s e)
{
// Put user code to initialize the page here
}

#region Web Form Designer generated code
override protected void OnInit(EventArg s e)
{
//
// CODEGEN: This call is required by the ASP.NET Web Form Designer.
//
InitializeCompo nent();
base.OnInit(e);
}

/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeCompo nent()
{
this.Button1.Cl ick += new System.EventHan dler(this.Butto n1_Click);
this.Load += new System.EventHan dler(this.Page_ Load);

}
#endregion

private ArrayList GetRowsArray()
{
ArrayList Ar = new ArrayList();
SqlConnection Conn = Common.GetConne ction("sonny");
string sql = "SELECT * from Sn_SalesReport" ;
SqlCommand Command = new SqlCommand(sql, Conn);
Command.Connect ion.Open();
SqlDataReader r = Command.Execute Reader();
while (r.Read())
{
string sqlstatement = r["sqlstateme nt"].ToString();
Ar.Add(sqlstate ment);
Response.Write( sqlstatement+"< br>");
}
r.Close();
Conn.Close();
return Ar;
}
private void Button1_Click(o bject sender, System.EventArg s e)
{
ArrayList Ar = GetRowsArray();
// create the Thread array
Thread[] t = new Thread[ Ar.Count ];
int lIdx;
ProcessSQL sr;

for ( lIdx = 0; lIdx < Ar.Count; lIdx ++ )
{
sr = new ProcessSQL(Ar[lIdx].ToString());
t[lIdx] = new Thread( new ThreadStart( sr.UpdateSalesR eport ) );
t[lIdx].Start();
}

for ( lIdx = 0; lIdx < Ar.Count; lIdx ++ )
{
// waiting for all the Threads to finish.
t[lIdx].Join();
}

}
}

public class ProcessSQL
{
private string sql;
public ProcessSQL (string sql)
{
this.sql = sql;
}

public void UpdateSalesRepo rt()
{
try
{
string Total_Dollar_Am ount = GetTotal(sql,"t est");
}
catch(Exception ex)
{
HttpContext.Cur rent.Response.W rite("Error#### ####: "+ex.Messag e);
}
}

public string GetTotal(string sql, string database)
{
sql = "Select reportname from SN_SalesReport" ;
string result = string.Empty;
try
{
SqlConnection Conn = Common.GetConne ction(database) ;
SqlCommand Command = new SqlCommand(sql, Conn);
Command.Connect ion.Open();
SqlDataReader r = Command.Execute Reader();
if(r.Read())
{
// gets total
result = r.GetString(0);
}
r.Close();
if (Conn!=null)
{
Conn.Close();
}

}
catch(Exception ex)
{
HttpContext.Cur rent.Response.W rite("Error#### ####: "+ex.Messag e);
}
return result;
}
}


}

[Jon Skeet [C# MVP]]

Rodusa <rc**********@y ahoo.com> wrote:

I am getting this exception error which is driving me nuts.
System.NullRefe renceException - Object reference not set to an instance
of an object

If I comment this line, I don't get any errors:
string Total_Dollar_Am ount = GetTotal(sql,"t est");

Rather than printing out just the message, print out the full stack
trace. That way you should be able to see which line of your code is
throwing the exception.

Note that to make your code more robust you should be using "using"
statements for your connection/command/data reader, rather than calling
Close directly. (Currently if an exception is thrown, the connection
isn't closed.)

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Rodrigo Lueneberg]

*** Sent via Developersdex http://www.developersdex.com ***

[Rodrigo Lueneberg]

Thanks Joh, but I am sorry, I don't have too much experience with
debuging in Asp.net. Could you please be more especific when you talk
about "print out the full stack
trace. " How do I do it? Furthermore, I have a feeling it is something
to do with ADO and threading. Whenever several threads because they are
trying to use the same database access method at the same time. I tried
to use thread.sleep before closing the connection, but it does not work.
I still get the exception. I am almost going back to a linear
programming. I need to get this stuff working by tomorrow.

Thank you

Rodrigo Lueneberg

*** Sent via Developersdex http://www.developersdex.com ***

[Rodrigo Lueneberg]

Thanks Joh, but I am sorry, I don't have too much experience with
debuging in Asp.net. Could you please be more especific when you talk
about "print out the full stack
trace. " How do I do it? Furthermore, I have a feeling it is something
to do with ADO and threading. Whenever several threads because they are
trying to use the same database access method at the same time. I tried
to use thread.sleep before closing the connection, but it does not work.
I still get the exception. I am almost going back to a linear
programming. I need to get this stuff working by tomorrow.

Thank you

Rodrigo Lueneberg

*** Sent via Developersdex http://www.developersdex.com ***

[Jon Skeet [C# MVP]]

Rodrigo Lueneberg <ro************ **@hotmail.com> wrote:

Thanks Joh, but I am sorry, I don't have too much experience with
debuging in Asp.net. Could you please be more especific when you talk
about "print out the full stack
trace. " How do I do it?
Well, you're currently printing out ex.Message. Instead, print out
ex.ToString().
Furthermore, I have a feeling it is something
to do with ADO and threading. Whenever several threads because they are
trying to use the same database access method at the same time. I tried
to use thread.sleep before closing the connection, but it does not work.
I still get the exception. I am almost going back to a linear
programming. I need to get this stuff working by tomorrow.

You shouldn't be trying to use the same connection from multiple
threads - if you're doing that, that's a mistake. You can, however, use
different connections from different threads.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Rodusa]

I tried ex.ToString(), but the exception is being thrown by Visual
Studio, before it reaches the application. And when I try to debug, it
says "There is no source code available for the current location".
That's is why I am lost. I don't have any way to figure out.
Regarding, the connections, I heard about threadpool? Is that what you
mean? I had the wrong thought that GetTotal method had a privated
instance of Conn and it should automatically create different calls in
memory, causing no problems with opening and closing different
connections when using threads. Howevever, if this is not what you are
thinking, how can I create multiple instance Conn in this scenario?

[Rodusa]

Jon, I did implement the "using as you said". It doesn't seem to be a
connection problem because when I comment the datareader block the page
runs with no problem. It looks like it is something to do with the
datareader. The problem is I can't create a new instance of the
datareader.

public string GetTotal(string sql, string database)
{

sql = "Select reportname from SN_SalesReport" ;
string result = string.Empty;
try
{
using (SqlConnection Conn = new
SqlConnection(C onfigurationSet tings.AppSettin gs[database]))
{
SqlCommand Command = new SqlCommand(sql, Conn);
Command.Connect ion.Open();
//using(SqlDataRe ader r = Command.Execute Reader())
{
// if(r.Read())
// {
// gets total
// result = r.GetString(0);
// }
// r.Close();
// if (Conn!=null)
// {
// Conn.Close();
// }
}
}

}
catch(Exception ex)
{
HttpContext.Cur rent.Response.W rite("Error#### ####:
"+ex.ToString() );
}
return result;
}

[Jon Skeet [C# MVP]]

Rodusa <rc**********@y ahoo.com> wrote:

I tried ex.ToString(), but the exception is being thrown by Visual
Studio, before it reaches the application. And when I try to debug, it
says "There is no source code available for the current location".
That's is why I am lost. I don't have any way to figure out.
Regarding, the connections, I heard about threadpool? Is that what you
mean?
No, not quite.
I had the wrong thought that GetTotal method had a privated
instance of Conn and it should automatically create different calls in
memory, causing no problems with opening and closing different
connections when using threads. Howevever, if this is not what you are
thinking, how can I create multiple instance Conn in this scenario?

I suspect the problem you're seeing isn't related to not using a using
statement - that was just a separate bug in your code which was worth
pointing out before it hit you.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Jon Skeet [C# MVP]]

Rodusa <rc**********@y ahoo.com> wrote:

Jon, I did implement the "using as you said". It doesn't seem to be a
connection problem because when I comment the datareader block the page
runs with no problem. It looks like it is something to do with the
datareader. The problem is I can't create a new instance of the
datareader.

What do you mean by "you can't create a new instance of the
datareader"? What happens when you try?

Note that the SqlCommand should be in a using block too, for
preference. (It probably doesn't matter, at least not at the moment,
but it's good practice.)

Also note that as you've got a using block, you don't need to call
Close on the connection or the reader - it disposes of them
automatically.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too