code: public boolean addNetworkConnectedListener(
  			NetworkConnectedListener listener) {
  		synchronized (this) {
  			if (connectedListeners.contains(listener)) {
  				return true;
  			}
  			return connectedListeners.add(listener);
  		}
  	}
docs: Registers Network Connection Listener<br>
  Once registered, connection listeners can be alerted when the device
  comes to have network connection
  
  @param listener
  Listener which implements INetworkConnectedListener
  @return true if already that listener is registered; false otherwise