title: android - service stops when activity is destroyed
body: <p>when I open the activity of my project I call the <code>startService(Intent intent)</code> method to start a new Service. 
  When the activity is destroyed the service shouldn't be killed (because I didn't use the <code>bindService()</code> method), but the fact is that when I close my activity the service is killed and after a second the system creates a new Service (I verified that, the system calls again the <code>onCreate()</code> method of my service). What do I have to do to keep only one service ? Thank you</p>