Android: How to communicate with .NET application via TCP

• Download source code (for Android Studio IDE) - 109 KB
• Download source code (for Eclipse IDE) - 25.1 KB

Related articles:

• Android: Fast Communication with .NET Using Protocol Buffers
• Remote Procedure Calls between Android and .NET
• Android: How to Receive Notification Messages from Multiple .NET Applications via Websockets

Introduction

The example bellow implements a simple request-response communication between Android and .NET application. The Android application is a simple client using the .NET application as a service to calculate length of the text message.

The example bellow uses Eneter Messaging Framework making the whole communication very simple. (The framework is free for noncommercial use and can be downloaded from http://www.eneter.net. You need to download Eneter for.NET and Eneter for Android. More detailed technical info can be found at technical info.)

To Run Example

If you use Android Studio:

1. Download the example for Android Studio (It contains the client project for Android Studio and the service project for Visual Studio).
2. Open NetService solution in Visual Studio.
3. If your Visual Stusio supports NuGet packages then just try to build the solution and the Eneter library will be downloaded automatically from NuGet.org server.
   If your Visual Studio does not support NuGet packages then you need to download Eneter Messaging Framework for .NET and unzip it. Then add the reference to the Eneter library. (Right click on 'References' then choose 'Add Reference ...' and navigate to the path where you have unzipped Eneter for .NET and choose the library for .NET 4.0)
4. Open AndroidNetCommunicationClientActivity in Android Studio.
5. Download Eneter Messaging Framework for Java and unzip it.
6. Copy eneter-messaging-android library to AndroidNetCommunicationClientActivity\app\libs.
7. Right click on the Eneter library and (from the bottom part of the context menu) choose 'Add As Library...'
8. Start Netervice from Visual Studio.
9. Start Android client from in Android Studio.

In addition if you use Android Studio 2.3 or higher you need to turn off the 'Instant Run' feature. (The problem is that this feature "secretly" adds the field with the name $change into classes which then causes problems to XmlSerializer.):

1. Open the Settings or Preferences dialog.
2. Navigate to Build, Execution, Deployment > Instant Run.
3. Uncheck the box next to Enable Instant Run.

If you use Eclipse:

1. Download the example for Eclipse (It contains the client project for Eclipse and the service project for Visual Studio).
2. Open NetService solution in Visual Studio.
3. If your Visual Stusio supports NuGet packages then just try to build the solution and the Eneter library will be downloaded automatically from NuGet.org server.
   If your Visual Studio does not support NuGet packages then you need to download Eneter Messaging Framework for .NET and add the reference to the Eneter library. (Right click on 'References' then choose 'Add Reference ...' and navigate to the path where you have unzipped Eneter for .NET and choose the library for .NET 4.0)
4. Open AndroidNetCommunicationClient in Eclipse.
5. Download Eneter Messaging Framework for Java and unzip it.
6. Right click on 'libs' and choose 'Import...' -> 'General/File System' -> 'Next'.
7. Then click 'Browser' button for 'From directory' and navigate to directory with the Eneter library.
8. Select the check box and press 'Finish'.
9. Start Netervice from Visual Studio.
10. Start Android client from in Android Studio.

TCP on Android

When you implement the communication via TCP on Android, you must count with two specifics:

If the permission is not set, the application is not allowed to communicate across the network. To set the INTERNET permission you must add the following line to AndroidManifest.xml.

<uses-permission android:name="android.permission.INTERNET"/>

An example of AndroidManifest.xml allowing communication across the network:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="net.client"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="7" />
    <uses-permission android:name="android.permission.INTERNET"/>

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:name=".AndroidNetCommunicationClientActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

The emulator acts as a separate device. Therefore, the IP address 127.0.0.1 is the loopback of that device and cannot be used for the communication with other applications running on the same computer as the emulator.

Instead of that you must use a real IP address of the computer or the emulator can use the special address 10.0.2.2 that is routed to 127.0.0.1 (loopback) on the computer. In my example, the Android emulator uses 10.0.2.2 and the .NET service is listening to 127.0.0.1.

1. You must set INTERNET permission for your Android application!
2. The IP address 127.0.0.1 (loopback) cannot be set on the Android emulator to communicate with the .NET application!

Android Client Application

The Android client is a very simple application allowing user to put some text message and send the request to the service to get back the length of the text. When the response message is received it must be marshalled to the UI thread to display the result. Also please do not forget to set android.permission.INTERNET.

The whole implementation is very simple with using the Eneter framework:

package net.client;

import eneter.messaging.diagnostic.EneterTrace;
import eneter.messaging.endpoints.typedmessages.*;
import eneter.messaging.messagingsystems.messagingsystembase.*;
import eneter.messaging.messagingsystems.tcpmessagingsystem.TcpMessagingSystemFactory;
import eneter.net.system.EventHandler;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.*;

public class AndroidNetCommunicationClientActivity extends Activity
{
    // Request message type
    // The message must have the same name as declared in the service.
    // Also, if the message is the inner class, then it must be static.
    public static class MyRequest
    {
        public String Text;
    }

    // Response message type
    // The message must have the same name as declared in the service.
    // Also, if the message is the inner class, then it must be static.
    public static class MyResponse
    {
        public int Length;
    }
    
    // UI controls
    private Handler myRefresh = new Handler();
    private EditText myMessageTextEditText;
    private EditText myResponseEditText;
    private Button mySendRequestBtn;
    
    
    // Sender sending MyRequest and as a response receiving MyResponse.
    private IDuplexTypedMessageSender<MyResponse, MyRequest> mySender;
    
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        // Get UI widgets.
        myMessageTextEditText = (EditText) findViewById(R.id.messageTextEditText);
        myResponseEditText = (EditText) findViewById(R.id.messageLengthEditText);
        mySendRequestBtn = (Button) findViewById(R.id.sendRequestBtn);
        
        // Subscribe to handle the button click.
        mySendRequestBtn.setOnClickListener(myOnSendRequestClickHandler);
        
        // Open the connection in another thread.
        // Note: From Android 3.1 (Honeycomb) or higher
        //       it is not possible to open TCP connection
        //       from the main thread.
        Thread anOpenConnectionThread = new Thread(new Runnable()
            {
                @Override
                public void run()
                {
                    try
                    {
                        openConnection();
                    }
                    catch (Exception err)
                    {
                        EneterTrace.error("Open connection failed.", err);
                    }
                }
            });
        anOpenConnectionThread.start();
    }
    
    @Override
    public void onDestroy()
    {
        // Stop listening to response messages.
        mySender.detachDuplexOutputChannel();
        
        super.onDestroy();
    } 
    
    private void openConnection() throws Exception
    {
        // Create sender sending MyRequest and as a response receiving MyResponse
        IDuplexTypedMessagesFactory aSenderFactory =
           new DuplexTypedMessagesFactory();
        mySender = aSenderFactory.createDuplexTypedMessageSender(MyResponse.class, MyRequest.class);
        
        // Subscribe to receive response messages.
        mySender.responseReceived().subscribe(myOnResponseHandler);
        
        // Create TCP messaging for the communication.
        // Note: 10.0.2.2 is a special alias to the loopback (127.0.0.1)
        //       on the development machine
        IMessagingSystemFactory aMessaging = new TcpMessagingSystemFactory();
        IDuplexOutputChannel anOutputChannel = 
           aMessaging.createDuplexOutputChannel("tcp://10.0.2.2:8060/");
        
        // Attach the output channel to the sender and be able to send
        // messages and receive responses.
        mySender.attachDuplexOutputChannel(anOutputChannel);
    }
    
    private void onSendRequest(View v)
    {
        // Create the request message.
        MyRequest aRequestMsg = new MyRequest();
        aRequestMsg.Text = myMessageTextEditText.getText().toString();
        
        // Send the request message.
        try
        {
            mySender.sendRequestMessage(aRequestMsg);
        }
        catch (Exception err)
        {
            EneterTrace.error("Sending the message failed.", err);
        }
    }
    
    private void onResponseReceived(Object sender, final TypedResponseReceivedEventArgs<MyResponse> e)
    {
        // Display the result - returned number of characters.
        // Note: Marshal displaying to the correct UI thread.
        myRefresh.post(new Runnable()
            {
                @Override
                public void run()
                {
                    myResponseEditText.setText(Integer.toString(e.getResponseMessage().Length));
                }
            });
    }
    
    private EventHandler<TypedResponseReceivedEventArgs<MyResponse>> myOnResponseHandler
            
         = new EventHandler<TypedResponseReceivedEventArgs<MyResponse>>()
    {
        @Override
        public void onEvent(Object sender,
                            TypedResponseReceivedEventArgs<MyResponse> e)
        {
            onResponseReceived(sender, e);
        }
    };
    
    private OnClickListener myOnSendRequestClickHandler = new OnClickListener()
    {
        @Override
        public void onClick(View v)
        {
            onSendRequest(v);
        }
    };
}

.NET Service Application

The .NET service is a simple console application listening to TCP and receiving requests to calculate the length of a given text.

The implementation of the service is very simple:

using System;
using Eneter.Messaging.EndPoints.TypedMessages;
using Eneter.Messaging.MessagingSystems.MessagingSystemBase;
using Eneter.Messaging.MessagingSystems.TcpMessagingSystem;

namespace ServiceExample
{
    // Request message type
    public class MyRequest
    {
        public string Text { get; set; }
    }

    // Response message type
    public class MyResponse
    {
        public int Length { get; set; }
    }

    class Program
    {
        private static IDuplexTypedMessageReceiver<MyResponse, MyRequest> myReceiver;

        static void Main(string[] args)
        {
            // Create message receiver receiving 'MyRequest' and receiving 'MyResponse'.
            IDuplexTypedMessagesFactory aReceiverFactory = new DuplexTypedMessagesFactory();
            myReceiver = aReceiverFactory.CreateDuplexTypedMessageReceiver<MyResponse, MyRequest>();

            // Subscribe to handle messages.
            myReceiver.MessageReceived += OnMessageReceived;

            // Create TCP messaging.
            IMessagingSystemFactory aMessaging = new TcpMessagingSystemFactory();
            IDuplexInputChannel anInputChannel = 
               aMessaging.CreateDuplexInputChannel("tcp://127.0.0.1:8060/");

            // Attach the input channel and start to listen to messages.
            myReceiver.AttachDuplexInputChannel(anInputChannel);

            Console.WriteLine("The service is running. To stop press enter.");
            Console.ReadLine();

            // Detach the input channel and stop listening.
            // It releases the thread listening to messages.
            myReceiver.DetachDuplexInputChannel();
        }

        // It is called when a message is received.
        private static void OnMessageReceived(object sender, 
              TypedRequestReceivedEventArgs<MyRequest> e)
        {
            Console.WriteLine("Received: " + e.RequestMessage.Text);

            // Create the response message.
            MyResponse aResponse = new MyResponse();
            aResponse.Length = e.RequestMessage.Text.Length;

            // Send the response message back to the client.
            myReceiver.SendResponseMessage(e.ResponseReceiverId, aResponse);
        }
    }
}

And here are applications communicating together: