How to add and update rows in gridview asp.net - asp.net

Question

I am doing an online ordering system. I want to check if the item exist in the gridview so it will not add another row or have multiple lines (It will update the qty and the price). The gridview is updating using dgvOrder.Rows[i].Cells[2].Text but my problem is how to update the datatable.
bool isExist = false;
if (Session["dtInSession"] != null)
dt = (DataTable)Session["dtInSession"]; //Getting datatable from session
for (int i = 0; i < dgvOrder.Rows.Count; i++)
{
if (dgvOrder.Rows[i].Cells[0].Text == b.ID)
{
isExist = true;
dgvOrder.Rows[i].Cells[2].Text = Convert.ToString(Convert.ToInt32(dgvOrder.Rows[i].Cells[2].Text) + 1);
dgvOrder.Rows[i].Cells[3].Text = Convert.ToString(Convert.ToInt32(dgvOrder.Rows[i].Cells[2].Text) * price);
}
}
if (!isExist)
{
DataRow dr = dt.NewRow();
dr["pCode"] = b.ID;
dr["desc"] = description;
dr["qty"] = "1";
dr["price"] = price;
dt.Rows.Add(dr);
dgvOrder.DataSource = dt;
dgvOrder.DataBind();
}
Because I am planning to pass the datatable using the session variable.
Session["orders"] = dt;
Response.Redirect("FinalizeOrder.aspx");
after passing the data, the code is working but only 1 qty for each item is passing.
Can anyone help me in this issue?

Answer 1

The problem is that you reload the DataSource of the GridView only if !isExist. Otherwise you are changing the datatable, but you are not assigning it to the GridView again, so the values are coming from the ViewState.
So this should work:
// update the table
// ...
if (!isExist)
{
// ...
}
// reassign the updated DataTable and DataBind the grid always
dgvOrder.DataSource = dt;
dgvOrder.DataBind();