title: Android: How do I avoid starting activity which is already in stack?
body: <p>Lets try to explain my question:
  I got an application and a service.
  The application is started with activity A.
  The service sends a broadcast that will let the application start Activity B
  Now the user starts activity C.</p>
  
  <p>Now the service wants to start activity B again. But how do I let him know that the activity is still on the stack, or is there an intent flag for this?</p>
  
  <p>How do I avoid that it will launch activity B because its already in the stack?</p>