Writing Game Center Apps in iOS

Reporting Scores to Leaderboards

Problem

You have created at least one leaderboard in iTunes Connect and now you want to store players’ scores to that leaderboard.

Solution

Use the reportScoreWithCompletionHandler: instance method of the GKScore class as demonstrated in the Discussion section.

Discussion

Assuming that you have already created a leaderboard (see Creating Leaderboards in iTunes Connect), you must follow these steps to report scores to it:

1. Authenticate the local player (see Authenticating the Local Player in Game Center).

2. Create an instance of the GKScore class and set the category of that score to the Leaderboard ID that you chose when you were creating this leaderboard.

3. Set the value property of the score object.

4. Use the reportScoreWithCompletionHandler: instance method of the GKScore class to report the error. This method accepts one parameter, which must be a block that returns void and accepts a parameter of type NSError. You can use this error to determine whether an error occurred during the process of reporting the score:

- (BOOL) reportScore:(NSUInteger)paramScore toLeaderboard:(NSString *)paramLeaderboard{ __block BOOL result = NO; GKLocalPlayer *localPlayer = [GKLocalPlayer localPlayer]; if ([localPlayer isAuthenticated] == NO){ NSLog(@"You must authenticate the local player first."); return NO; } if ([paramLeaderboard length] == 0){ NSLog(@"Leaderboard identifier is empty."); return NO; } GKScore *score = [[[GKScore alloc] initWithCategory:paramLeaderboard] autorelease]; ...