Why my DataTables in DataSet are cleared?

[Kevin.Li]

I am using ASP.NET 2.0.

My DataTable in DataSet are cleared automatically!

The follow is my code:
//--------------- I just keep what core part related to the
problem-----------------------------------------
using System;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Web;
using System.Web.UI;

public partial class _Default : System.Web.UI.Page
{
DataTable ds = new DataSet();
string cs = "Data Source=.;Initial Catalog=Northwind;Integrated
Security=True";

protected void Button1_Click(object sender, EventArgs e)
{
string ss = "select
CompanyName,ContactName,ContactTitle,Country,HomePage,Fax,Phone from
Suppliers where "+ selColumn + " = '" + selValue+" ' ";
SqlDataAdapter sda = new SqlDataAdapter(ss,cs);
sda.Fill(ds,"suppliers"); // Everything works well here,
int test = ds.Tables.Count // test will be assigned to
1.
}
protected void btnFirst_Click(object sender, EventArgs e)
{

int test = ds.Tables.Count; // test is 0! Where did my
"suppliers" table gone?
if (ds.Tables["suppliers"].Rows.Count > 0) // Hence, exception:
NullReferenceException.
{
// to do something;
}
}

I still have reference in dataset to the datatable, how can the
datatable be released?

Please help me.. Thanks !

 

[Kalpesh]

Are you clicking btnFirst without clicking on Button1 by mistake?

Kalpesh

 

[Kevin.Li]

Are you clicking btnFirst without clicking on Button1 by mistake?

Kalpesh

Kalpesh,Thanks for your quick reply.

I was not clicking btnFirst without clicking on Button1 by mistake. I
had tested several times before asking for help.

I understand the reason now.

That was because:

When I click another button on the page, I will generate *new* request
to the server, which means the code-behind will be re-executed.
therefore :

public partial class _Default : System.Web.UI.Page
{
int test = 0; // Set a break-point
here, you find out everything.
DataTable ds = new DataSet(); // When click the btnSave button,
dtData will be assigned to null.
...
...

}

Kalpesh , thanks again.

 

[Kalpesh]

My bad. For the moment, I missed the point that it is asp.net

Kalpesh

 

[Peter Bromberg [C# MVP]]

In addition to your announced discovery vis-a-vis ASP.NET, consider fixing up
this line:

DataTable ds = new DataSet();

You are typing "ds" as a DataTable and then you proceed to instantiate it as
a DataSet? That won't work at all.
-- Peter
Site: http://www.eggheadcafe.com
UnBlog: http://petesbloggerama.blogspot.com
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