title: ios11 game center find player fails
body: <p>I am developing a multi player game. I want to use "standard" GKMatchmakerViewController for finding players like this: </p>
  
  <pre><code>let matchrequest = GKMatchRequest()
  matchrequest.minPlayers = 2
  matchrequest.maxPlayers = 2
  matchrequest.defaultNumberOfPlayers = 2
  matchrequest.inviteMessage = "Hello, do you want to play with me ?"
  
  let mmVC = GKMatchmakerViewController(matchRequest: matchrequest)
  mmVC?.matchmakerDelegate = self
  self.present(mmVC!, animated: true)
  </code></pre>
  
  <p>If I invoke the GKMatchmakerViewController on both devices and press "Play now" they find each other and everything ist fine.</p>
  
  <p>However when I press "Invite Friends", press the "+" on the right to add a recipient and go then to the tab "Nearby" NO players show up. </p>
  
  <p>Q1: Why don't I see the player in "Nearby" but can connect to it by pressing "Play now"</p>
  
  <p>Q2: If I send an invitation to my other player via iMessage the message is received on the other device and when I click it the app gets launched. But it remains at its Main Screen and doesn't take any action to respond to the invitation. What Protocol or Callback needs to be implemented in order to react to app launches caused by "game invitations" ?</p>
  
  <p>Please refer to the latest API. The GC APIs have changed dramatically and most SO answers refer to the deprecated API.</p>
  
  <p>Thanks
  Chris</p>