如何使用 executeScalar() 在 executeReader() 中使用 asp.net 使用 C#

我收到错误：

"已经有一个与此命令关联的打开的 DataReader 必须先关闭。

代码如下：

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我正在使用 1 个表生成动态表，在该表的每一行中，我希望从另一个表

进行总和计算我首先使用 sqlcommand "cmd" 和 ExecuteReader() 调用readDr()。
之后，我调用了使用 sqlcommand "cmdTotAmt" & ExecuteScalar() 的CalTotAmt(string CC)。
我已经使用了 2 个差异 sqlcommand 仍然给出错误。

protected void readDr()
{
        string str = "select CCNo,TotalAmt,NoOfRect,Energy,New1,Theft,Misc from ChallanTable;";
        cmd = new SqlCommand(str, con);
        rdr = cmd.ExecuteReader();      
}

protected void CreateChallanTable()
{
        table.Caption = "Challan Entry";
        table.ID = "Challan Entry";
        table.BackColor = System.Drawing.Color.Maroon;
        table.ForeColor = System.Drawing.Color.Gray;
        readDr();      //call to function readDr()
        Panel2.Controls.Add(table);
        for (i = 0; i < 1; i++)
        {
            row = new TableRow();
            row.BorderStyle = BorderStyle.Ridge;
            m = 0;
            while (rdr.Read())
            {
                row = new TableRow();
                row.ID = "Row" + m;
                row.BorderStyle = BorderStyle.Ridge;
                for (n = 0; n <= 6; n++)
                {
                    cell = new TableCell();
                    cell.ID = "cell" + m + n;
                    cell.BorderWidth = 5;
                    cell.BorderStyle = BorderStyle.Ridge;
                    //cell.BorderColor = System.Drawing.Color.Azure;
                    for (n = 0; n <= 0; n++)
                    {
                        Label lbl = new Label();
                        lbl.ID = "lblCCRow" + m + n;
                        lbl.Text = Convert.ToString(rdr[0]);
                        lbl.Width = 70;
                        CCNo = lbl.Text;
                        // Add the control to the TableCell
                        cell.Controls.Add(lbl);
                    }
                    for (n = 1; n <= 1; n++)
                    {
                        Label lbl = new Label();
                        lbl.ID = "lblTotAmt" + m + n;
                        lbl.Text = Convert.ToString(rdr[1]);
                        lbl.Width = 70;
                        TotAmt = Convert.ToDouble(lbl.Text);
                        // Add the control to the TableCell
                        cell.Controls.Add(lbl);
                        Label2.Text = Convert.ToString(CalTotAmt(CCNo));
                    }
                    for (n = 2; n <= 2; n++)
                    {
                        Label lbl = new Label();
                        lbl.ID = "lblNoRect" + m + n;                            
                        lbl.Text = Convert.ToString(rdr[2]);
                        lbl.Width = 70;
                        NoofRects = Convert.ToDouble(lbl.Text);
                        // Add the control to the TableCell
                        cell.Controls.Add(lbl);
                    }
                    for (n = 2; n <= 2; n++)
                    {
                        Label lbl = new Label();
                        lbl.ID = "lblEnergy" + m + n;
                        lbl.Text = Convert.ToString(rdr[3]);
                        lbl.Width =70;
                        Energy = Convert.ToDouble(lbl.Text);
                        // Add the control to the TableCell
                        cell.Controls.Add(lbl);
                    }
                    for (n = 3; n <= 3; n++)
                    {
                        Label lbl = new Label();
                        lbl.ID = "lblNew" + m + n;
                        lbl.Text = Convert.ToString(rdr[4]);
                        lbl.Width =70;
                        NewSD = Convert.ToDouble(lbl.Text);
                        // Add the control to the TableCell
                        cell.Controls.Add(lbl);
                    }
                    for (n = 4; n <= 4; n++)
                    {
                        Label lbl = new Label();
                        lbl.ID = "lblTheft" + m + n;
                        lbl.Text = Convert.ToString(rdr[5]);
                        lbl.Width = 70;
                        Theft = Convert.ToDouble(lbl.Text);
                        // Add the control to the TableCell
                        cell.Controls.Add(lbl);
                    }
                    for (n = 5; n <= 5; n++)
                    {
                        Label lbl = new Label();
                        lbl.ID = "lblMisc" + m + n;
                        lbl.Text = Convert.ToString(rdr[6]);
                        lbl.Width = 70;
                        Misc = Convert.ToDouble(lbl.Text);
                        // Add the control to the TableCell
                        cell.Controls.Add(lbl);
                    }
                    row.Cells.Add(cell);
                }
                // Add the TableRow to the Table
                table.Rows.Add(row);
                //dr.NextResult();
                //outer for-loop end     
                m++;
            }
            rdr.Close();         
}
protected double CalTotAmt(string CC)
{
    double Total = 0;
    string str = "select Sum(Amount) from MainDataTable Where CC='" + CC + "' and BU ='" + LogInBU + "'";
    SqlCommand cmdTotAmt = new SqlCommand(str,con);
    Total = Convert.ToDouble(cmdTotAmt.ExecuteScalar());
    Label2.Text = Total.ToString();
    return Total;
}

请帮帮我。

protected DataTable readDr()
{
        con.Open();
        string str = "select CCNo,TotalAmt,NoOfRect,Energy,New1,Theft,Misc from ChallanTable;";
        cmd = new SqlCommand(str, con);
        rdr = cmd.ExecuteReader();
        DataTable dt = new DataTable(); 
        dt.Load(rdr);
        rdr.Close();
        con.Close();
}

select CCNo,TotalAmt,NoOfRect,Energy,New1,Theft,Misc,SumTotal
from ChallanTable ct
      cross apply
     (select Sum(Amount) as SumTotal from MainDataTable Where CC=ct.CCNo) t