WP - pass the id from one page to next page depends upon selecteditem in windows phone

if (isset($_POST['product_id']) && isset($_POST['customer_id'])) {
    $product_id = $_POST['product_id'];
    $customer_id = $_POST['customer_id'];
   

    // mysql update row with matched pid
    $result = mysql_query("DELETE FROM pim_productdeal WHERE product_id = $product_id AND customer_id = $customer_id");

private void client_UploadStringCompleted(object sender, UploadStringCompletedEventArgs e)
        {
            if (e.Cancelled == false && e.Error == null)
            {
                MemoryStream ms = new MemoryStream(Encoding.UTF8.GetBytes(e.Result));
                ObservableCollection<Member> list = new ObservableCollection<Member>();
                DataContractJsonSerializer serializer = new DataContractJsonSerializer(typeof(ObservableCollection<Member>));
                list = (ObservableCollection<Member>)serializer.ReadObject(ms);

                List<Member> myCustomer = new List<Member>();
                foreach (var cm in list)
                {
                    string scustomerID = cm.customer_id;
                    sproductID = cm.product_id;
                    sproduct_name = cm.product_name.ToString();
                   

                    myCustomer.Add(new Member(scustomerID, sproductID, sproduct_name));
                }

 private void Remove(object sender, RoutedEventArgs e)
        {
            NavigationService.Navigate(new Uri("/DeletewatchList.xaml?sproductid=" + sproductID, UriKind.Relative));
        }

  private void MainPage_Loaded(object sender, System.Windows.RoutedEventArgs e)
         {
             MessageBoxResult result = MessageBox.Show("Are you sure want to delete?", "Delete Message", MessageBoxButton.OKCancel);
             if (result == MessageBoxResult.OK)
             {
               
                 string url = "http://www.bestinuk.com/BestinUk_Windows/deleteproduct.php";
                 Uri uri = new Uri(url, UriKind.Absolute);
                 NavigationContext.QueryString.TryGetValue("sproductid", out sproductID);
                 StringBuilder postData = new StringBuilder();
                 postData.AppendFormat("{0}={1}", "product_id", HttpUtility.UrlEncode(InputList.sproductID));
                 postData.AppendFormat("&{0}={1}", "customer_id", HttpUtility.UrlEncode(LoginPage.strcustomer_id_k));
                
                 WebClient client = default(WebClient);
                 client = new WebClient();
                 client.Headers[HttpRequestHeader.ContentType] = "application/x-www-form-urlencoded";
                 client.Headers[HttpRequestHeader.ContentLength] = postData.Length.ToString();

                 client.UploadStringCompleted += client_UploadStringComplete;
                 client.UploadProgressChanged += client_UploadProgressChangedes;

                 client.UploadStringAsync(uri, "POST", postData.ToString());

                 prog = new ProgressIndicator();
                 prog.IsIndeterminate = true;
                 prog.IsVisible = true;
                 prog.Text = "Loading....";
                 SystemTray.SetProgressIndicator(this, prog);
             }
             else
             {
                 NavigationService.Navigate(new Uri("/InputList.xaml?selectedItem=", UriKind.Relative));
             }