Android Socket programming

Question

I am trying to connect android app(client) with java application(server 'PC') here is my client side code.

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    btn = (Button) findViewById(R.id.button1);
    txt = (EditText) findViewById(R.id.editText1);

    btn.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View arg0) {
            new CallServer().execute();
        }
    });
}

public class CallServer extends AsyncTask<String, Integer, String> {

    @Override
    protected String doInBackground(String... arg0) {
        String modifiedSentence = "hello";
        Socket clientSocket;
        try {
            clientSocket = new Socket("192.168.1.100", 8081);


            DataOutputStream outToServer = new DataOutputStream(
                    clientSocket.getOutputStream());
            BufferedReader inFromServer = new BufferedReader(
                    new InputStreamReader(clientSocket.getInputStream()));

            outToServer.writeBytes("hello world");

            modifiedSentence = 
            (inFromServer.readLine());

            clientSocket.close();

        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return modifiedSentence;
    }

    protected void onPostExecute(String result) {
        txt.setText(result);
    }
}

Android permission

<uses-sdk
    android:minSdkVersion="8"
    android:targetSdkVersion="17" />
<uses-permission android:name="android.permission.INTERNET"/>

I cant find the problem with this code as it does not give any type of warring or error my server side code is perfectly working as I have tested it with other java application (client side). There isn't any kind of port issue as well because I have tested it by keeping client and server side code on different machines and it worked fine.

Answer 1

The issue was with my server side code. I didn't closed the BufferedReader so now it works fine.

Answer 2

It's obvious it's not a router-firewall related problem as you are under the same net, so there are only a few possibilities:

• There's nothing listening on that port on that IP on the server-side
• There's a local firewall on the server-side that is blocking that connection attempt
• You are not using WIFI so you're not under the same net.

You should make sure you can open that service some ther way, that would help you debugging where the culprit is. If you've already done this, I'd suggest using some debugging tool to trace TCP packets (I don't know either what kind of operating system you use on the destination machine; if it's some linux distribution, tcpdump might help).

Answer 3

You can not modify UI elements such as your txt from doInBackground because it's a different thread.

Make doInBackground return your socket data and set your txt in onPostExecute

Answer 4

use invoke( new methodinvoker(delegate {})) like C#