Problem in report viewer Multiple Records in wpf

Hi,

     I have one datagrid and button(name btnview),in datagird i have checkbox in all rows,now i select(checked) the checkbox and click the button means it shows payslip for that particular employee in report viewer...if i select(checked) more than one checkboxs means it will shows all checked(select) employee payslip but it will shows only one employee payslip i dont know reason of that....Please help me...

My c# coding..for that button..

private void btnview_Click(object sender, RoutedEventArgs e)
        {
            string month="";
            int year=0;
            DataTable dt2 = new DataTable();
            string ids = string.Empty;
            report r = new report();
            con = new SqlConnection(cn);
            con.Open();
            foreach (DataRow dr in dt.Rows)
            {
                if (Convert.ToBoolean(dr["ischecked"]))
                {
                    SqlCommand cmd = new SqlCommand("viewpayslip", con);
                    cmd.CommandType = CommandType.StoredProcedure;
                    cmd.Parameters.AddWithValue("@pid",int.Parse(dr["p_id"].ToString()));
                    cmd.Parameters.AddWithValue("@month", dr["pmonth"].ToString());
                    cmd.Parameters.AddWithValue("@year",Int32.Parse(dr["pyear"].ToString()));
                    //dt2 = new DataTable();
                    SqlDataAdapter da = new SqlDataAdapter(cmd);
                    da.Fill(dt2);
                    //ids += dr["p_id"].ToString() + ",";
                    month = dr["pmonth"].ToString();
                    year = Int32.Parse(dr["pyear"].ToString());
                }
                
            }
            r.viewpay(dt2, month,year);
            r.Show();
            con.Close();
            //MessageBox.Show("Selected ids: " + ids.Trim(','));

        }