how to assign ConnectionString to a SqlDataSource within the namespace?

hi

i am trying to assignConnectionString to aSqlDataSource within thenamespace but i am getting this error

plz advise

Object reference not set to an instance of an object.

namespace myNameSpace
{

public partial class NRP : System.Web.UI.Page
{

SqlDataSource sds1;

protected void Page_PreInit(object sender, EventArgs e)
{
sds1= new SqlDataSource();
sds1.ID = "sds1";
this.Controls.Add(sds1);

sds1.ConnectionString = ConfigurationManager.ConnectionStrings["my_conn_str"].ToString();

}
}
}

namespace myNameSpace
{

public partial class NRP : System.Web.UI.Page
{


protected void Page_PreInit(object sender, EventArgs e)
{
SqlDataSource sds1= new SqlDataSource();
sds1.ID = "sds1";
this.Controls.Add(sds1);

sds1.ConnectionString = ConfigurationManager.ConnectionStrings["my_conn_str"].ToString();

}
}
}