How to update data to Mobile Services - Windows Phone (Windows Azure)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Navigation;
using Microsoft.Phone.Controls;
using Microsoft.Phone.Shell;

using Microsoft.WindowsAzure.MobileServices;
using Newtonsoft.Json;

namespace myPhoneApp
{
    public partial class UpdatePage : PhoneApplicationPage
    {

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

        public UpdatePage()
        {
            InitializeComponent();
        }

        private async void InfoMember()
        {
            try
            {
                
                NavigationContext.QueryString.TryGetValue("sid", out id);

                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
                {
                    MessageBox.Show("Not found Data!");
                }
            }
            catch (MobileServiceInvalidOperationException ex)
            {
                MessageBox.Show("Error : " + ex.Message);
            }
        }

        protected override void OnNavigatedTo(NavigationEventArgs e)
        {
            InfoMember();
        }

        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);

                MessageBox.Show("Update Data Successfully.");
                NavigationService.Navigate(new Uri("/MainPage.xaml", UriKind.Relative));

            }
            catch (MobileServiceInvalidOperationException ex)
            {
                MessageBox.Show("Error : " + ex.Message);
            }


        }

    }
}