adding dynamic row wid unique id retrieved in the textbox

[hello12356789]

private void AddRecordToGrid()
{
try
{


if (Session["SampleDataTable"] == null)
{
dt.Columns.Add(new DataColumn("ID", typeof(string)));
dt.Columns.Add(new DataColumn("Qtr", typeof(string)));

dt.Columns.Add(new DataColumn("Exp", typeof(string)));
dt.Columns.Add(new DataColumn("Partner", typeof(string)));
dt.Columns.Add(new DataColumn("Net", typeof(string)));
dr = dt.NewRow();
}
else
{
dt= (DataTable)Session["SampleDataTable"];
}

dr = dt.NewRow();


if (dr.IsNull(0))
{
//dr = dt.NewRow();
dr[0] = txtD.Text;
dr[1] = cbQuarter.SelectedItem.Text;

dr[2] =Exp.Text;
dr[3] = txtPartner.Text;
dr[4] = lblNet.Text;
dt.Rows.Add(dr);
DataView dv = new DataView(dt);
grdBudget.DataSource = dv;
grdBudget.DataBind();
}
for (int i = 0; i < grdBudget.Rows.Count; i++)
{

if (!dr.IsNull(0))
{
if (txtBudgetID.Text != dr[0].ToString())
{
dr = dt.NewRow();
dr[0] = txtD.Text;
dr[1] = cboQuarter.SelectedItem.Text;

dr[2] = Exp.Text;
dr[3] = txtPartner.Text;
dr[4] = lblNet.Text;
dt.Rows.Add(dr);
DataView dv = new DataView(dt);
grdBudget.DataSource = dv;
grdBudget.DataBind();
}
}
}
Session["SampleDataTable"] = dt;

}


catch (Exception ex)
{
}


the problem i m facing wid this code id that the new data row is added every time when this function is called and it enters ito the loop of the if(dr.isnull(0)) . i want only the values with unique id shud be entered. if the value wid the existin id id entere, it shud not be allowed to enter.