static void unregister(final Context context, final String regId) {
   Log.i(TAG, "unregistering device (regId = " + regId + ")");
   String serverUrl = SERVER_URL + "/unregister";
   Map<String, String> params = new HashMap<String, String>();
   params.put("regId", regId);
   try {
     post(serverUrl, params);
     GCMRegistrar.setRegisteredOnServer(context, false);
     String message = context.getString(R.string.server_unregistered);
     CommonUtilities.displayMessage(context, message);
   } catch (IOException e) {
     String message = context.getString(R.string.server_unregister_error, e.getMessage());
     CommonUtilities.displayMessage(context, message);
   }
 }
  static boolean register(final Context context, final String regId) {
    Log.i(TAG, "registering device (regId = " + regId + ")");
    String serverUrl = SERVER_URL + "/register";
    Map<String, String> params = new HashMap<String, String>();
    params.put("regId", regId);
    long backoff = BACKOFF_MILLI_SECONDS + random.nextInt(1000);

    for (int i = 1; i <= MAX_ATTEMPTS; i++) {
      Log.d(TAG, "Attempt #" + i + " to register");
      try {
        displayMessage(context, context.getString(R.string.server_registering, i, MAX_ATTEMPTS));
        post(serverUrl, params);
        GCMRegistrar.setRegisteredOnServer(context, true);
        String message = context.getString(R.string.server_registered);
        CommonUtilities.displayMessage(context, message);
        return true;
      } catch (IOException e) {
        // Here we are simplifying and retrying on any error; in a real
        // application, it should retry only on unrecoverable errors
        // (like HTTP error code 503).
        Log.e(TAG, "Failed to register on attempt " + i, e);
        if (i == MAX_ATTEMPTS) {
          break;
        }
        try {
          Log.d(TAG, "Sleeping for " + backoff + " ms before retry");
          Thread.sleep(backoff);
        } catch (InterruptedException e1) {
          // Activity finished before we complete - exit.
          Log.d(TAG, "Thread interrupted: abort remaining retries!");
          Thread.currentThread().interrupt();
          return false;
        }
        // increase backoff exponentially
        backoff *= 2;
      }
    }
    String message = context.getString(R.string.server_register_error, MAX_ATTEMPTS);
    CommonUtilities.displayMessage(context, message);
    return false;
  }