Invalid attempt to read when no data is present

I want to creat dynamic <asp:table ID=""...> and I want to have a totalAmount column by reading the first cell from my datareader and put it into total, this column must show the cumulative numbers....

try
{
    sqlconnection();
    sqlcommand("", sqlconnection);
    sqlconnection.open();
    sqldatereader dr;
    dr = sqlcommand.executereader();
    if (dr.HasRows)
    {
        //create column names;
      开发者_开发知识库  table_ShowReport.Rows.Add(new TableRow());
        table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Add(new TableCell());
        table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells[table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Count - 1].BorderWidth = 2;
        table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells[table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Count - 1].Text = "Amount";

        table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Add(new TableCell());
        table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells[table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Count - 1].BorderWidth = 2;
        table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells[table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Count - 1].Text = "Total";


        //here I wantend to get the initial value to my total:
        double total = double.parse(dr["amount"].tostring());

        while (dr.Read())
        {
            table_ShowReport.Rows.Add(new TableRow());
            table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Add(new TableCell());
            table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells[table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Count - 1].BorderWidth = 2;
            table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells[table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Count - 1].Text = dr["amount"].tostring();

            table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Add(new TableCell());
            table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells[table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Count - 1].BorderWidth = 2;
            table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells[table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Count - 1].Text = total.tostring();


            total += double.parse(dr["amount"].tostring());
        }
    }
    sqlconnection.close();
}
catch (exception ex)
{
    respose.write(ex.message);
}

but it shown me this error:

Invalid attempt to read when no data is present.

Please help me. Thanks

Tanya

You must call dr.Read() before you attempt to read from the SqlDataReader.

I suggest initializing your total variable with zero before reading the rows. Then set the total with the updated amount after calling dr.Read() but before displaying the total amount. Like this:

     double runningTotal = 0d;
     while (dr.Read())
     {
         table_ShowReport.Rows.Add(new TableRow());
         table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Add(new TableCell());
         table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells[table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Count - 1].BorderWidth = 2;
         table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells[table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Count - 1].Text = dr["amount"].ToString();
         table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Add(new TableCell());
         table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells[table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Count - 1].BorderWidth = 2;
         runningTotal += double.Parse(dr["amount"].ToString());
         table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells[table_ShowReport.Rows[table_ShowReport.Rows.Count - 1].Cells.Count - 1].Text = runningTotal.ToString();
     }
 }
 sqlconnection.Close(); 

Here is the complete code refactored a little bit so it's more clear:

    private static void PopulateReport(Table table, string connection)
    {
        table.Rows.Clear();
        PopulateReportRow(table, "Amount", "Total");            

        string commandText = @"...";

        using (SqlConnection conn = new SqlConnection(connection))
        {
            conn.Open();
            using (SqlCommand comm = new SqlCommand(commandText, conn))
            {
                using (SqlDataReader reader = comm.ExecuteReader())
                {
                    double total = 0d;
                    while (reader.Read())
                    {
                        double amount = (double)reader["amount"];
                        total += amount;
                        PopulateReportRow(table, amount.ToString("N"), total.ToString("N"));
                    }
                }
            }
        }
    }

    private static void PopulateReportRow(Table table, string amountValue, string totalValue)
    {
        const int cellBorderWidth = 2;

        int rowIndex = table.Rows.Add(new TableRow());

        TableCell amountCell = new TableCell();
        table.Rows[rowIndex].Cells.Add(amountCell);
        amountCell.BorderWidth = cellBorderWidth;
        amountCell.Text = amountValue;

        TableCell totalCell = new TableCell();
        table.Rows[rowIndex].Cells.Add(totalCell);
        totalCell.BorderWidth = cellBorderWidth;
        totalCell.Text = totalValue;
    }

You're trying to read from the reader before you get to the first row.

You should set it to 0 and populate it in the loop s you're doing now.

protected void Btnlogin_Click(object sender, EventArgs e)

{

    SqlConnection con=newSqlConnection("connection string"); 
    SqlCommand cmd = new SqlCommand();
    cmd.CommandText = "select * from tbluser where username='" + txtusername + "' and passworde='" + txtpassworde + "'";
    cmd.Connection = con;
    if (con.State == ConnectionState.Closed) con.Open();
    SqlDataReader dr = cmd.ExecuteReader();
    while (dr.Read())
    {
       if (dr["username"] == txtusername.Text.Trim() && dr["passworde"] == txtpassworde)
        {
            Response.Redirect("kala.aspx");
            return;
        }

   }
}

Code is correct but does not enter the next page