How to update data to Mobile Services - Windows Store App (Windows Azure)

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;

using Microsoft.WindowsAzure.MobileServices;
using Newtonsoft.Json;
using Windows.UI.Popups;

// The Blank Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=234238

namespace myApp
{
    /// <summary>
    /// An empty page that can be used on its own or navigated to within a Frame.
    /// </summary>
    public sealed partial class UpdatePage : Page
    {

        private MobileServiceCollection<MyMember, MyMember> items;
        private IMobileServiceTable<MyMember> memberTable = App.MobileService.GetTable<MyMember>();
        string id;

        public UpdatePage()
        {
            this.InitializeComponent();
        }

        /// <summary>
        /// Invoked when this page is about to be displayed in a Frame.
        /// </summary>
        /// <param name="e">Event data that describes how this page was reached.  The Parameter
        /// property is typically used to configure the page.</param>
        protected override void OnNavigatedTo(NavigationEventArgs e)
        {
            id = e.Parameter as string;
            InfoMember();
        }

        private async void InfoMember()
        {
            try
            {

                items = await memberTable
                .Where(memberItem => memberItem.Id == Convert.ToInt32(id))
                .ToCollectionAsync();

                if (items.Count > 0)
                {
                    MyMember member = items[0];
                    txtUsername.Text = member.Username.ToString();
                    txtPassword.Password = member.Password.ToString();
                    txtName.Text = member.Name.ToString();
                    txtEmail.Text = member.Email.ToString();
                    txtTel.Text = member.Tel.ToString();
                }
                else
                {
                    MessageDialog msgDialog = new MessageDialog("Not found Data!", "Error :");
                    await msgDialog.ShowAsync();
                }
            }
            catch (MobileServiceInvalidOperationException ex)
            {
                throw ex;
            }
        }

        private async void btnSave_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                //** Get Item for Update ***/
                items = await memberTable
                .Where(memberItem => memberItem.Id == Convert.ToInt32(id))
                .ToCollectionAsync();

                MyMember member = items[0];
                member.Name = txtName.Text;
                member.Password = txtPassword.Password;
                member.Name = txtName.Text;
                member.Email = txtEmail.Text;
                member.Tel = txtTel.Text;

                //*** Update Record ***/
                await memberTable.UpdateAsync(member);

                // Dialog
                MessageDialog msgDialog = new MessageDialog("Update Data Successfully.", "Status :");
                await msgDialog.ShowAsync();
                this.Frame.Navigate(typeof(MainPage), member.Id.ToString());

            }
            catch (MobileServiceInvalidOperationException ex)
            {
                throw ex;
            }
        }

    }
}