Android application unable to run on emulator

Question

I'm quite new to android development, I'm trying to develop a server-client application where the server is a simple java application that reads some text from a file and sends it using output stream. the client is an android application that reads this stream when clicking a button and displays it on a text view.

I'm using eclipse with ADK, and testing on an emulator here's how both codes look like:

Server:

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;


public class Server {
     /**
     * @param args
     * @throws IOException 
     * @throws UnknownHostException 
     */
    public static void main(String[] args) throws UnknownHostException, IOException 
    {

        System.out.println("***********Starting ***********");
        ServerSocket servsock = new ServerSocket(12344);
        System.out.println("Waiting...");

        Socket sock = servsock.accept();
        while (true) 
        {
          System.out.println("Accepted connection : " + sock);
          File myFile = new File ("source.txt");
          while (true){
          byte [] mybytearray  = new byte [(int)myFile.length()];
          FileInputStream fis = new FileInputStream(myFile);
          BufferedInputStream bis = new BufferedInputStream(fis);
          bis.read(mybytearray,0,mybytearray.length);
           OutputStream os = sock.getOutputStream();
          System.out.println("Sending...");
          os.write(mybytearray,0,mybytearray.length);
          os.flush();

          }    
    }

    }
}

Client:

-MainActivity

package com.example.streamerclient;

import android.app.Activity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;


public class MainActivity extends Activity implements OnClickListener {
         Button ConnectBtn ;

          @Override
          public void onResume() {
            super.onResume();
            //setContentView(R.layout.activity_main);

            System.out.println(" on resume ");
            ConnectBtn = (Button)findViewById(R.id.ConnectButton);

            ConnectBtn.setOnClickListener(this);

            }
          @Override
          public void onPause() {
            super.onPause(); 
          }
        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub

            Connecting c = new Connecting();

        }

}

-Connecting class

    package com.example.streamerclient;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.Socket;

import android.app.Activity;
import android.widget.TextView;

public class Connecting extends Activity implements Runnable 
{
    private Socket sock;
    private BufferedReader r;
    private BufferedWriter out;
    TextView Data;
    public Connecting ()
    {
        Data = (TextView) findViewById(R.id.DataTextView);
        Thread th = new Thread(this);
        th.start();

    }
    @Override
    public void run() {
        try
        {

        System.out.println("trying to initiated ");
        Data.setText("trying to initiated ");
        sock = new Socket("10.0.2.2",12344);
        System.out.println(" socket initiated ");
        Data.setText(" socket initiated ");
        r = new BufferedReader(new InputStreamReader(sock.getInputStream()));
        Data.setText("  buffer reader initiated  ");
        System.out.println(" buffer reader initiated ");

        out = new BufferedWriter(new OutputStreamWriter(sock.getOutputStream()));
        Data.setText("   buffer writer initiated  ");
        System.out.println(" buffer writer initiated ");
        final String data = r.readLine(); 
        Data.setText("   Data read is: \n"+data);
        System.out.println(" Data read is: \n"+data);        
        }
        catch (IOException ioe) { }
    }
 public void OnPause()
 {
     System.out.println(" paused");
        try {
          if (sock != null) {
            sock.getOutputStream().close();
            sock.getInputStream().close();
            sock.close();
            System.out.println(" everything is closed ");
          }
        } catch (IOException e) {}
 }
}

I know I know, there are some parts of the code that are not used .. my next task is to have this application send commands to the server ... so I'm still experimenting.

when running the application on the emulator it stops before even displaying any of the GUI components. Any idea why ? Here's what the log file says

03-17 08:16:30.886: W/Trace(846): Unexpected value from nativeGetEnabledTags: 0
03-17 08:16:30.886: W/Trace(846): Unexpected value from nativeGetEnabledTags: 0
03-17 08:16:30.886: W/Trace(846): Unexpected value from nativeGetEnabledTags: 0
03-17 08:16:31.016: W/Trace(846): Unexpected value from nativeGetEnabledTags: 0
03-17 08:16:31.016: W/Trace(846): Unexpected value from nativeGetEnabledTags: 0
03-17 08:16:31.126: I/System.out(846):  on resume 
03-17 08:16:31.447: D/AndroidRuntime(846): Shutting down VM
03-17 08:16:31.447: W/dalvikvm(846): threadid=1: thread exiting with uncaught exception (group=0x40a70930)
03-17 08:16:31.457: E/AndroidRuntime(846): FATAL EXCEPTION: main
03-17 08:16:31.457: E/AndroidRuntime(846): java.lang.RuntimeException: Unable to resume activity {com.example.streamerclient/com.example.streamerclient.MainActivity}: java.lang.NullPointerException
03-17 08:16:31.457: E/AndroidRuntime(846):  at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2742)
03-17 08:16:31.457: E/AndroidRuntime(846):  at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2771)
03-17 08:16:31.457: E/AndroidRuntime(846):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2235)
03-17 08:16:31.457: E/AndroidRuntime(846):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
03-17 08:16:31.457: E/AndroidRuntime(846):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
03-17 08:16:31.457: E/AndroidRuntime(846):  at android.os.Handler.dispatchMessage(Handler.java:99)
03-17 08:16:31.457: E/AndroidRuntime(846):  at android.os.Looper.loop(Looper.java:137)
03-17 08:16:31.457: E/AndroidRuntime(846):  at android.app.ActivityThread.main(ActivityThread.java:5039)
03-17 08:16:31.457: E/AndroidRuntime(846):  at java.lang.reflect.Method.invokeNative(Native Method)
03-17 08:16:31.457: E/AndroidRuntime(846):  at java.lang.reflect.Method.invoke(Method.java:511)
03-17 08:16:31.457: E/AndroidRuntime(846):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
03-17 08:16:31.457: E/AndroidRuntime(846):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
03-17 08:16:31.457: E/AndroidRuntime(846):  at dalvik.system.NativeStart.main(Native Method)
03-17 08:16:31.457: E/AndroidRuntime(846): Caused by: java.lang.NullPointerException
03-17 08:16:31.457: E/AndroidRuntime(846):  at com.example.streamerclient.MainActivity.onResume(MainActivity.java:20)
03-17 08:16:31.457: E/AndroidRuntime(846):  at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1185)
03-17 08:16:31.457: E/AndroidRuntime(846):  at android.app.Activity.performResume(Activity.java:5182)
03-17 08:16:31.457: E/AndroidRuntime(846):  at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2732)
03-17 08:16:31.457: E/AndroidRuntime(846):  ... 12 more

thanks!

Answer 1

Try moving the contents of your entire onResume() to an onCreate() method. Always do the UI setup in onCreate(). Read this: Activity Lifecycle Management .

And take any further queries to stackoverflow :)

Cheers!

Answer 2

You are getting a NullPointerException on line 20 in MainActivity, check that line.
I think this question is better suited for stackoverflow