WP8.1两个应用之间UDP通讯的有关问题，新手求指教

WP8.1两个应用之间UDP通讯的问题，新手求指教
为什么运行时，两个应用第一次发的信息无法显示出来，后面的就正常了呢？请指教

两个代码只是端口号不同
第一个应用代码：

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
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 Windows.Devices.Geolocation;
using Windows.System;
using Windows.UI.Popups;
using Windows.Networking.Sockets;
using Windows.Networking;
using Windows.Storage.Streams;

// The Blank Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=402352&clcid=0x409

namespace UpdTest2
{
	/// <summary>
	/// An empty page that can be used on its own or navigated to within a Frame.
	/// </summary>
	public sealed partial class MainPage : Page
	{

		const string LOCAL_PORT = "12200"; 
		DatagramSocket updSocket = null;
		IOutputStream outStream = null;

		bool isUdpSocketInitializzed = false;


		public MainPage()
		{
			this.InitializeComponent();

			this.txtRemoteIP.Text = "127.0.0.1";
			this.txtRemotePort.Text = "12201";
		}

		private async void btnSend_Click(object sender, RoutedEventArgs e)
		{
			if (outStream==null ||
				string.IsNullOrWhiteSpace(txtToSend.Text))
			{
				return;
			}
			DataWriter writer = new DataWriter(outStream);
			writer.UnicodeEncoding = UnicodeEncoding.Utf8;
			writer.WriteString(txtToSend.Text);
			await writer.StoreAsync();
			writer.DetachStream();
			writer.Dispose();
			await new MessageDialog("Done").ShowAsync();
			txtToSend.Text = "";
		}

		protected async override void OnNavigatedTo(NavigationEventArgs e)
		{
			if (!isUdpSocketInitializzed)
			{
				updSocket = new DatagramSocket();
				updSocket.MessageReceived += MessageReceived;
				await updSocket.BindServiceNameAsync(LOCAL_PORT);
				isUdpSocketInitializzed = true;
			}
			base.OnNavigatedTo(e);
		}

		async void MessageReceived(DatagramSocket sender, DatagramSocketMessageReceivedEventArgs args)
		{
			DataReader reader = args.GetDataReader();
			uint len = reader.UnconsumedBufferLength;
			string message = reader.ReadString(len);

			string host = string.Format("{0}:{1}", args.RemoteAddress.DisplayName, args.RemotePort);
			await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
			 {
				 listView.Items.Add("From" + host + " Message:" + message);
			 });
		}

		private async void btnBind_Click(object sender, RoutedEventArgs e)
		{
			if (string.IsNullOrWhiteSpace(txtRemoteIP.Text) ||
				string.IsNullOrWhiteSpace(txtRemotePort.Text))
			{
				return;
			}
			HostName remoreHostName = new HostName(txtRemoteIP.Text);
			try
			{
				outStream = await updSocket.GetOutputStreamAsync(remoreHostName, txtRemotePort.Text)
				btnSend.IsEnabled = true;
			}catch(Exception ex)
			{
				await new MessageDialog(ex.Message.ToString()).ShowAsync();
			}
	
		}
	}
}

第二个代码：

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
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 Windows.Devices.Geolocation;
using Windows.System;
using Windows.UI.Popups;
using Windows.Networking.Sockets;
using Windows.Networking;
using Windows.Storage.Streams;

// The Blank Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=402352&clcid=0x409

namespace App7
{
	/// <summary>
	/// An empty page that can be used on its own or navigated to within a Frame.
	/// </summary>
	public sealed partial class MainPage : Page
	{

		const string LOCAL_PORT = "12201"; 
		DatagramSocket udpSocket = null;
		IOutputStream outStream = null;

		bool isUdpSocketInitializzed = false;


		public MainPage()
		{
			this.InitializeComponent();

			this.txtRemoteIP.Text = "127.0.0.1";
			this.txtRemotePort.Text = "12200";

		}

		private async void btnSend_Click(object sender, RoutedEventArgs e)
		{
			if (outStream==null ||
				string.IsNullOrWhiteSpace(txtToSend.Text))
			{
				return;
			}
			DataWriter writer = new DataWriter(outStream);
			writer.UnicodeEncoding = UnicodeEncoding.Utf8;
			writer.WriteString(txtToSend.Text);
			await writer.StoreAsync();
			writer.DetachStream();
			writer.Dispose();
			await new MessageDialog("Done").ShowAsync();
			txtToSend.Text = "";
		}

		protected async override void OnNavigatedTo(NavigationEventArgs e)
		{
			if (!isUdpSocketInitializzed)
			{
				udpSocket = new DatagramSocket();
				udpSocket.MessageReceived += MessageReceived;
				await udpSocket.BindServiceNameAsync(LOCAL_PORT);
				isUdpSocketInitializzed = true;
			}
			base.OnNavigatedTo(e);
		}

		async void MessageReceived(DatagramSocket sender, DatagramSocketMessageReceivedEventArgs args)
		{
			DataReader reader = args.GetDataReader();
			uint len = reader.UnconsumedBufferLength;
			string message = reader.ReadString(len);

			string host = string.Format("{0}:{1}", args.RemoteAddress.DisplayName, args.RemotePort);
			await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
			 {
				 listView.Items.Add("From" + host + " Message:" + message);
			 });
		}

		private async void btnBind_Click(object sender, RoutedEventArgs e)
		{
			if (string.IsNullOrWhiteSpace(txtRemoteIP.Text) ||
				string.IsNullOrWhiteSpace(txtRemotePort.Text))
			{
				return;
			}
			HostName remoteHostName = new HostName(txtRemoteIP.Text);
			try
			{
				outStream = await udpSocket.GetOutputStreamAsync(remoteHostName, txtRemotePort.Text);
				btnSend.IsEnabled = true;
			}catch(Exception ex)
			{
				await new MessageDialog(ex.Message.ToString()).ShowAsync();
			}
			
		}
	}
}

------解决思路----------------------
这个太强了，UDP通讯。从来没搞过。