Wsrtjtyk

I'm trying to establish a socket connection between my Android smartphone and an external custom device by using the Xamarin framework. This external device is supposed to accept some custom commands and return a response. This works fine with a Telnet client such as Tera Term. However, I didn't have any luck with my Xamarin code so far. It looks as follows:

using Microsoft.AspNetCore.Http;

using System;

using System.Diagnostics;

using System.Linq;

using System.Net;

using System.Net.Sockets;

using System.Net.WebSockets;

using System.Text;

using System.Threading;

using System.Threading.Tasks;

using Xamarin.Forms;



namespace MyNamespace

{

    public partial class MainPage : ContentPage

    {

        private Socket mySocket;



        public MainPage()

        {

            InitializeComponent();

        }



        private bool ConnectToSocketAndReturnConnectionStatus(Socket socket, IPEndPoint remoteEndPoint)

        {

            try

            {

                socket.Connect(remoteEndPoint);

            }

            catch (Exception e)

            {

                Debug.WriteLine("Exception: Network subsystem is down", e);

            }



            return socket.Connected;

        }



        private void AcceptCallback(IAsyncResult ar)

        {

            // Receive from socket

            byte buffer = new byte[1024];

            int iRx = mySocket.Receive(buffer);

            char chars = new char[iRx];



            Decoder d = Encoding.UTF8.GetDecoder();

            int charLen = d.GetChars(buffer, 0, iRx, chars, 0);

            String recv = new String(chars);

            DisplayAlert("Message from Socket", recv, "OK");

        }



        private void SendMyCommand()

        {

            byte byData = Encoding.ASCII.GetBytes("DataStringOfMyCommand");

            mySocket.Send(byData);

            DisplayAlert("Message from Socket", "My command sent", "OK");

        }



        void ConnectButtonClicked(object sender, EventArgs args)

        {

            // Init socket

            mySocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

            IPAddress ipAdd = IPAddress.Parse("x.x.x.x");

            IPEndPoint remoteEndPoint = new IPEndPoint(ipAdd,myPortNumber);



            bool mySocketIsConnected = ConnectToSocketAndReturnConnectionStatus(mySocket, remoteEndPoint);



            if (mySocketIsConnected) {

                DisplayAlert("Message from Socket", "Connection successfully established", "OK");

                try

                {

                    mySocket.Blocking = false;

                    mySocket.Listen(100);

                    mySocket.BeginAccept(new AsyncCallback(AcceptCallback), mySocket);

                }

                catch (Exception e)

                {

                    Debug.WriteLine(e.ToString());

                }

            }

            else { DisplayAlert("Message from Socket", "No connection possible. Check your network!", "OK"); }

        }



        void MyCommandButtonClicked(object sender, EventArgs args)

        {

            SendMyCommand();

        }

    }

}

The alert message "Connection successfully established" pops up as expected. Thus, I suppose that the external device is at least found. However, I'm not able to see the response as no alert pop-up is displayed once I send my custom command. Apparently, the function "AcceptCallback(...)" is never called. What am I doing wrong here?

Your help is very much appreciated.

P.S: Here is the corresponding .xaml file, just in case you are wondering how the UI looks like:

<?xml version="1.0" encoding="utf-8" ?>

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"

             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"

             xmlns:local="clr-namespace:MyNamespace"

             x:Class="MyNamespace.MainPage"

             Title="My Tool">



    <StackLayout>

        <Label x:Name="label"

               Text="Welcome"

               FontSize="Medium"

               VerticalOptions="CenterAndExpand"

               HorizontalOptions="Center" />



        <Button Text="Connect to hardware"

                VerticalOptions="CenterAndExpand"

                HorizontalOptions="Center"

                Clicked="ConnectButtonClicked" />



        <Button Text="Send my command"

                VerticalOptions="CenterAndExpand"

                HorizontalOptions="Center"

                Clicked="MyCommandButtonClicked" />



    </StackLayout>



</ContentPage>