Question

I am developing an online multiplayer game, but I am struggling with Apple documentation. (I have tried these tutorials by Ray Wenderlichs Part 1 and part 2, but they are not working (match never starts because inviting device never receives the match acceptance).

As this topic is vast, I will be creating a single question, then moving to create another question on SO if necessary.

I want to create an online multiplayer game that will let a user to invite from 1 to 3 people. So, it would be a 2 to 4 people match. The game is not turned based. It is live and the data to be transferred between users is minimum.

Lets start with the basic stuff.

1) the first thing I do is create a notification

if (self.gameCenterAvailable) {
    NSNotificationCenter *nc = 
    [NSNotificationCenter defaultCenter];
    [nc addObserver:self 
           selector:@selector(authenticationChanged) 
               name:GKPlayerAuthenticationDidChangeNotificationName 
             object:nil];

}

to let me know when the notification changes. When this happens, authenticationChanged method will fire… here it is

- (void)authenticationChanged {    

GKMatchmaker sharedMatchmaker].inviteHandler = ^(GKInvite *acceptedInvite, NSArray *playersToInvite) {
   // Insert application-specific code here to clean up any games in progress.
   if (acceptedInvite)
    {
        GKMatchmakerViewController *mmvc = [[[GKMatchmakerViewController alloc] initWithInvite:acceptedInvite] autorelease];
        mmvc.matchmakerDelegate = self;
        [self presentModalViewController:mmvc animated:YES];
    }
    else if (playersToInvite)
    {
        GKMatchRequest *request = [[[GKMatchRequest alloc] init] autorelease];
        request.minPlayers = 2;
        request.maxPlayers = 4;
        request.playersToInvite = playersToInvite;

        GKMatchmakerViewController *mmvc = [[[GKMatchmakerViewController alloc] initWithMatchRequest:request] autorelease];
        mmvc.matchmakerDelegate = self;
        [self presentModalViewController:mmvc animated:YES];
    }
};

}

I grabbed this code from Apple. My question here is this. If Apple say to run this code after the user is authenticated why it is checking for invitation or users to invite? As far as I see, users were not invited yet. Unless the code is not executed at that time, right? It will just sit in memory waiting to be called, WHEN the invitation is done, correct?

If this is the case, I now create an invitation for a match doing

[self dismissModalViewControllerAnimated:NO];
GKMatchRequest *request = [[[GKMatchRequest alloc] init] autorelease]; 
request.minPlayers = minPlayers;     
request.maxPlayers = maxPlayers;
request.playersToInvite = self.pendingPlayersToInvite;

GKMatchmakerViewController *mmvc = [[[GKMatchmakerViewController alloc] initWithMatchRequest:request] autorelease];    
mmvc.matchmakerDelegate = self;

[self presentModalViewController:mmvc animated:YES];

A window will be present to all users I choose to invite. Suppose the first one taps ACCEPT on the invitation. Which method will be fired on my app, how do I get the user identity and how do I know if all users accepted?

thanks.

Answer 1

First of all please be aware that invitations on the Sandbox enviroment tend to work erratically, so I suggest you start by having all players search for an available match. The code would be something like this:

GKMatchRequest *request = [[[GKMatchRequest alloc] init] autorelease];
request.minPlayers = minPlayers;
request.maxPlayers = maxPlayers;

[[GKMatchmaker sharedMatchmaker] findMatchForRequest:request
                               withCompletionHandler:^(GKMatch *match, NSError *error) {
                                     if (error || !match) {
                                       // handle the error
                                     }
                                     else if (match != nil){
                                       // match found
                                     }}];
  }

Then you have to implement the protocol GKMatchDelegate. There’s a method there that will be invoked for each player that joins the match and for each player that gets disconnected from it (on this method you can find out the user identity with its playerID):

- (void)match:(GKMatch *)match player:(NSString *)playerID didChangeState:(GKPlayerConnectionState)state {
    switch (state){
      case GKPlayerStateConnected: 
        if (match.expectedPlayerCount == 0) {
          // start the match
        }
        break;
      case GKPlayerStateDisconnected:
        // remove the player from the match, notify other players, etc
        break;
    } 
}

Regarding your first question, the code on authenticationChanged is only registering the handlers for those methods, meaning the code that will be invoked when the notifications arrive.

EDIT: Regarding the question on your comment, if the match was started by invitations, the user that started the match has to wait until all invitations are accepted, or cancel some of them and then press Start Match (or something like that) on the Invite Screen. In this scenario the match.expectedPlayerCount == 0 condition will be satisfied once all the players that accepted the invites are connected to the match.
If the match was started by AutoMatch then Game Center does the following: once it finds minPlayers waiting to start a match it will assign them to a match and then wait a few more seconds to see if it can fill the remaining slots. At some point it will start the match with a certain number of players between minPlayers and maxPlayers. Then the condition match.expectedPlayerCount == 0 will be satisfied only once all the players have effectively join the match, but note that when the decision was taken to start a match the number of players expected for that match is already determined by Game Center.