iOS 6 Game Center authenticateHandler can't login after a cancel

Question

When using the authenticateHandler in iOS 6, game center won\'t present the login view if the user cancels it. I realize game center will auto lockout an app after 3 cancel

Answer 1

Better use runtime checks (instancesRespondToSelector:) instead of preprocessor #if statements, so that you can use recommended methods where they are available and depreciated ones elsewhere. I actually found I need to distinguish three cases before setting the invite handler, as the authentication handler might also get called with a nil view controller:

 -(void)authenticateLocalPlayer
 {
     if ([[GKLocalPlayer class] instancesRespondToSelector:@selector(setAuthenticateHandler:)]) {
         [[GKLocalPlayer localPlayer] setAuthenticateHandler:^(UIViewController *gameCenterLoginViewController, NSError *error) {
             if (gameCenterLoginViewController) {
                 [self.presentedViewController presentViewController:gameCenterLoginViewController
                                                            animated:YES
                                                          completion:^{
                                                              [self setInviteHandlerIfAuthenticated];
                                                          }];
             } else {
                 [self setInviteHandlerIfAuthenticated];
             }
         }];
     } else { // alternative for iOS < 6
         [[GKLocalPlayer localPlayer] authenticateWithCompletionHandler:^(NSError *error) {
             [self setInviteHandlerIfAuthenticated];
         }];
     }
 }

Yet more cases must be distinguished within the invite handler, as matchForInvite:: is new in iOS6 as well and avoids yet another round through game center view controllers:

-(void)setInviteHandlerIfAuthenticated
{
    if ([GKLocalPlayer localPlayer].isAuthenticated) {
        [GKMatchmaker sharedMatchmaker].inviteHandler = ^(GKInvite *acceptedInvite, NSArray *playersToInvite) {
            if (acceptedInvite) {
                if ([GKMatchmaker instancesRespondToSelector:@selector(matchForInvite:completionHandler:)]) {
                    [self showInfoAnimating:YES completion:NULL];
                    [[GKMatchmaker sharedMatchmaker] matchForInvite:acceptedInvite
                                                  completionHandler:^(GKMatch *match, NSError *error) {
                                                      // ... handle invited match
                                                  }];
                } else {
                    // alternative for iOS < 6
                    GKMatchmakerViewController *mmvc = [[[GKMatchmakerViewController alloc] initWithInvite:acceptedInvite] autorelease];
                    mmvc.matchmakerDelegate = self;
                    // ... present mmvc appropriately
                    // ... handle invited match found in delegate method matchmakerViewController:didFindMatch:
                 }
            } else if (playersToInvite) {
                 // ... handle match initiated through game center
            }
        };
    }
}

Let me know if this helps.

Answer 2

I dont' think this is possible in iOS 6.0. There were API calls to do this in the early SDK builds that were removed before release.

In the WWDC 2012 Video: Session 516 - Integrating Your Games with Game Center [8:30] They actually show code where you call an authenticate method:

GKLocalPlayer *localPlayer = [GKLocalPlayer localPlayer];
localPlayer.authenticationHandler = //handle the callback...
[localPlayer authenticate];

This method is now private API but you can see it in action by calling:

[[GKLocalPlayer localPlayer] performSelector:@selector(_authenticate)];

It does exactly what you want, but can't be used because it's now private.

---

You can also trigger the authentication process by posting the UIApplicationWillEnterForegroundNotification notification:

[[NSNotificationCenter defaultCenter] postNotificationName:UIApplicationWillEnterForegroundNotification object:[UIApplication sharedApplication]];

I assume it would be unadvisable to do this in live code.