How to retrieve value of a Templated Field text box in GridView?

Dotnetstudent

Hi,

I am developing shopping cart in my website. If the user selects any product from DetailsView details like ProductID, Description and Price should be stored in a datatable. All this is working perfectly fine. Upon clicking CheckOut button I am navigated to another page where I have used the contents of the same datatable as well as additional data from database. Here, I have used templated field text box to store quantity entered by the user. My problem is, on clicking Check Price button I am not able to retrieve its value. At run time, it shows NullReferenceException. I have provided the source code for the page in which Templated text field exists. Can anyone help me with the correct code?
Is this code snippet correct:
TextBox tb =(TextBox)GridView1.Rows[i].Cells[0].FindControl("tempqty");
string unit = tb.Text;
int u = Convert.ToInt32(unit);

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public partial class Purchase : System.Web.UI.Page

{

SqlConnection con;

public void Page_Load(object sender, EventArgs e)

{

string s = ConfigurationManager.ConnectionStrings["myconstring"].ConnectionString;

con = new SqlConnection(s);

if (!Page.IsPostBack)

{

DataTable dt1 =(DataTable)Session["MyDataTable"];

dt1.Columns.Add("Discount");

dt1.Columns.Add("Total Price");

GridView1.DataSource = dt1;

GridView1.DataBind();

int row = GridView1.Rows.Count;

int i;

for (i = 0; i < row; i++)

{

SqlCommand cmd = new SqlCommand("select ddiscount from dconfiguration where configid='" + GridView1.Rows[i].Cells[1].Text + "'", con);

con.Open();

SqlDataReader dr = cmd.ExecuteReader();



while (dr.Read())

GridView1.Rows[i].Cells[4].Text = dr[0].ToString();

dr.Close();

con.Close();

}

}

}



protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)

{

foreach (TableCell c in e.Row.Cells)

{
c.ForeColor = System.Drawing.Color.Violet;
c.BackColor = System.Drawing.Color.Yellow;
}

GridView1.BorderColor = System.Drawing.Color.YellowGreen;



}



protected void checkPrice_Click(object sender, EventArgs e)

{

int row1 = GridView1.Rows.Count;

int i;

for (i = 0; i < row1; i++)

{

string price = GridView1.Rows[i].Cells[2].Text;

string discount = GridView1.Rows[i].Cells[3].Text;

int price_len = price.Length;

string p = price.Substring(0, price_len - 3);

string p1=p.Replace(",", String.Empty);

int discount_len = discount.Length;

string d = discount.Substring(0, discount_len - 1);

TextBox tb = (TextBox)GridView1.Rows[i].Cells[0].FindControl("tempqty");

string unit = tb.Text;

int u = Convert.ToInt32(unit); //getting error NullReferenceException

int price1 = Convert.ToInt32(p1);

float discount1 = Convert.ToInt16(d);

double x = (discount1 / 100);

double tot = u * (price1 - (price1 * (x)));

GridView1.Rows[i].Cells[5].Text = tot.ToString();



}

}
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