在Android设备上打开套接字

Question

I know this seems a repeated question but it is not actually. I want to communicate with some sensors over sockets. The connection work fine on Emulator but when I upload it on Android Device it wont work. After Debugging I narrowed my app down to simple opening a socket using the following code.

try
{
 Socket socket = new Socket(InetAddress.getByName(ipAddress).getHostAddress(), 10001);
}
catch (Exception e)
{
 Toast.makeText(context, "Error: "+e.getMessage(), duration).show();
}

I am simply opening a socket.This works fine on the emulator but when I run this app on the device it hangs for some time and shows me nothing not even the exception message... Any Idea what could be the problem. (Initially it was StrictMode problem but I sorted out). No error on the LogCat. I have installed android terminal emulator and tried ping, reply is fine. Thanks in advance

---

This is the code

import java.net.InetAddress;
import java.net.Socket;

import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.StrictMode;
import android.view.View;
import android.view.Window;
import android.widget.Button;
import android.widget.TextView;
import android.view.View.OnClickListener;

public class MainActivity extends Activity implements OnClickListener {
    Button btn;
    private CharSequence text = "";
    private Socket s;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder()
        .detectDiskReads()
        .detectDiskWrites()
        .detectNetwork()   // or .detectAll() for all detectable problems
        .penaltyLog()
        .build());
        StrictMode.setVmPolicy(new StrictMode.VmPolicy.Builder()
        .detectLeakedSqlLiteObjects()
        .detectLeakedClosableObjects()
        .penaltyLog()
        .penaltyDeath()
        .build());

        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);
        btn = (Button) findViewById(R.id.button1);
        btn.setOnClickListener(this);
    }

    public void onClick(View view){
        //detect the view that was "clicked"
        switch(view.getId())
        {
          case R.id.button1:
              new LongOperation().execute("");
          break;

        }

    }

    private class LongOperation extends AsyncTask<String, Void, String> {

          @Override
          protected String doInBackground(String... params) {

              try {
                    s = new Socket(InetAddress.getByName("o2215.airq.org").getHostAddress(), 10001);
                    text = "Connection Made";
                } catch (Exception e) {
                    text = "Error : ";
                    for(int i=0;i<e.getStackTrace().length;i++)
                    {
                        text = text +"\n"+ e.getStackTrace()[i];
                    }
                    e.printStackTrace();
                }
                return "";
          }      

          @Override
          protected void onPostExecute(String result) {
                TextView txt = (TextView) findViewById(R.id.output);
                txt.setText(text);
          }
    }
}

This works fine on the emulator, but not on the device.

Answer 1

Perhaps, this is because you try to make a connection in the main UI thread. Looks like you place the above code snippet inside your Activity class.

You should create a separate thread to make communications with network.

Use either simple Thread or Android's wonderful AsyncTask