I am a fairly beginner in Android Development. I am developing an application that extensively relays on Webservice calls. First screen takes username and password and validates the user by calling the Webservice. If U/P is valid, then I need to fire up the 2nd activity. In that 2nd activity, I need to do 3 calls. But I haven't gotten to the 2nd part yet. In fact, I haven't completed the full coding yet. But I wanted to test if the app is working as far as I've come through.

When calling webserivce, I am showing alert dialog. But the app is crashing somewhere. The LoginActivity shows up. When I enter U/P and press Login Button, it crashes.

My classes:

TaskHandler.java

 public class TaskHandler {

private String URL;
private User userObj;
private String results;
private JSONDownloaderTask task; ;

public TaskHandler( String url, User user) {
    this.URL = url;
    this.userObj = user;
}

public String handleTask() {
    Log.d("Two", "In the function");
    task = new JSONDownloaderTask();
    Log.d("Three", "In the function");
    task.execute(URL);
    return results;
}

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

    private String username;// = userObj.getUsername();
    private String password; //= userObj.getPassword();

    public  HttpStatus status_code;

    public JSONDownloaderTask() {
        Log.d("con", "Success");
        this.username = userObj.getUsername();
        this.password = userObj.getPassword();

        Log.d("User" + this.username , " Pass" + this.password);
    }

    private AsyncProgressActivity progressbar = new AsyncProgressActivity();

    @Override
    protected void onPreExecute() {
        progressbar.showLoadingProgressDialog();
    }

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

        final String url = params[0]; //getString(R.string.api_staging_uri) + "Authenticate/";

        // Populate the HTTP Basic Authentitcation header with the username and password
        HttpAuthentication authHeader = new HttpBasicAuthentication(username, password);
        HttpHeaders requestHeaders = new HttpHeaders();
        requestHeaders.setAuthorization(authHeader);
        requestHeaders.setAccept(Collections.singletonList(MediaType.APPLICATION_JSON));

        // Create a new RestTemplate instance
        RestTemplate restTemplate = new RestTemplate();

        restTemplate.getMessageConverters().add(new MappingJacksonHttpMessageConverter());

        try {
            // Make the network request
            Log.d(this.getClass().getName(), url);

            ResponseEntity<Message> response = restTemplate.exchange(url, HttpMethod.GET, new HttpEntity<Object>(requestHeaders), Message.class);
            status_code =  response.getStatusCode();
            return response.getBody().toString();
        } catch (HttpClientErrorException e) {

            status_code = e.getStatusCode();
            return new Message(0, e.getStatusText(), e.getLocalizedMessage(), "error").toString();
        } catch ( Exception e ) {
            Log.d(this.getClass().getName()  ,e.getLocalizedMessage());
            return "Unknown Exception";
        }
    }


    @Override
    protected void onPostExecute(String result) {
        progressbar.dismissProgressDialog();


        switch ( status_code ) {
        case UNAUTHORIZED:
            result =  "Invalid username or passowrd"; break;
        case ACCEPTED:
            result = "Invalid username or passowrd" + status_code; break;
        case OK:
            result = "Successful!"; break;
        }
    }
}
}

AsycProgressActivity.java

public class AsyncProgressActivity  extends Activity {

protected static final String TAG = AsyncProgressActivity.class.getSimpleName();

private ProgressDialog progressDialog;
private boolean destroyed = false;

@Override
protected void onDestroy() {
    super.onDestroy();
    destroyed = true;
}

public void showLoadingProgressDialog() {
    Log.d("Here", "Progress");
    this.showProgressDialog("Authenticating...");
    Log.d("Here", "afer p");
}

public void showProgressDialog(CharSequence message) {
    Log.d("Here", "Message");
    if (progressDialog == null) {
        progressDialog = new ProgressDialog(this);
        progressDialog.setIndeterminate(true);
    }
    Log.d("Here", "Message 2");

    progressDialog.setMessage(message);
    progressDialog.show();
}

public void dismissProgressDialog() {
    if (progressDialog != null && !destroyed) {
        progressDialog.dismiss();
    }
}
}

LoginActivity.java

public class LoginActivity extends AsyncProgressActivity implements OnClickListener {

Button login_button;
HttpStatus status_code;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //this.requestWindowFeature(Window.FEATURE_NO_TITLE);

    setContentView(R.layout.main);

    login_button = (Button) findViewById(R.id.btnLogin);
    login_button.setOnClickListener(this);
    ViewServer.get(this).addWindow(this); 
}

public void onDestroy() {  
    super.onDestroy();  
    ViewServer.get(this).removeWindow(this);  
}  

public void onResume() {  
    super.onResume();  
    ViewServer.get(this).setFocusedWindow(this);  
}  

public void onClick(View v) {
    if ( v.getId() == R.id.btnLogin ) {

        User userobj = new User();
        String result;
        userobj.setUsername( ((EditText) findViewById(R.id.username)).getText().toString());
        userobj.setPassword(((EditText) findViewById(R.id.password)).getText().toString() );


        TaskHandler handler = new TaskHandler(getString(R.string.api_staging_uri) + "Authenticate/", userobj);
        Log.d(this.getClass().getName(), "One");
        result = handler.handleTask();
        Log.d(this.getClass().getName(), "After two");
        Utilities.showAlert(result, LoginActivity.this);
    }
}

Utilities.java

public class Utilities {

public static void showAlert(String message, Context context) {

    AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(context);
    alertDialogBuilder.setTitle("Login");

    alertDialogBuilder.setMessage(message)
                      .setCancelable(false)
                      .setPositiveButton("OK",new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog,int id) {
                            dialog.dismiss();
                            //dialog.cancel();
                        }
                       });
    alertDialogBuilder.setIcon(drawable.ic_dialog_alert);

    // create alert dialog
    AlertDialog alertDialog = alertDialogBuilder.create();

    // show it
    alertDialog.show(); 
}
 }