If I have an app that supports Game Center and I'd like to provide Achievements for completing a puzzle pack that's sold as an in-app purchase, how do I sync the iTunes account that's being charged for the in-app purchase with the Game Center user account that's doing the buying? As I understand it, they're two separate user accounts that are accessed in two different locations (The Game Center account is accessed in the Game Center app and the iTunes account is accessed in the Settings app).
How do I avoid this from happening...
Game Center Player1 logs in, runs my app and purchases a puzzle pack
Game Center Player1 logs out, Game Center Player2 logs in, runs my app and plays to completion the puzzle pack that Player1 purchased and Player2 is awarded the Achievement.
Game Center Player2 logs out, Game Center Player1 logs in and finds the puzzle pack he/she purchased as already completed, so Player1 is unable to gain that same achievement.
Am I misunderstanding something with how these user accounts work? If not, is there a way to sync a Game Center account with an iTunes account as players log in and out of my game? Is there any kind of a work around for this problem? This seems like it would be a fairly common issue with any multiplayer games that sell content.
Thanks so much!
That is a good question. :) As far as achievements go, I guess you could store them on the device with the playerId from the logged in GKPlayer, and once an achievement has been finished for a logged in player, you synch with Game Center.
As far as synching iTunes and Game Center accounts I really don't know. Usually you store some information on whether a purchase has been made (i.e. a feature available) on the device. Would it be logical that using that feature (or being allowed to use it) should be device dependent, not GC user dependent? But then what happens if someone uses their account to just download your content again and again to their friends' devices?
Hmm... I hope some other people will share their thoughts on this. But I found that Game Center questions receive very low views and answers :(
So here's how I'm going to do this, it's actually a fairly straightforward approach. I'm going to locally track users progress in the purchased puzzle packs using core data, since it's quick to get up and running. Each time a new GC user logs in, I'll create a new user object and track their progress in the puzzle packs and report the achievements in GC when needed. When that GC user logs in later, I'll just adjust the state of the puzzle packs to match their current progress defined in core data. This way, any iTunes account can purchase the puzzle packs and they'll inherently be available to anyone using the device. Whenever any GC users log into GC and play my app, they'll all have access to the same purchased puzzle packs, but their progress and achievements will be maintained independently of other GC users.
If GC isn't installed on the device, I can disable all GC features and just init the app as tho there's only one default player.
Should be simple to do.
I am trying to come up with the solution to resolve this issue as well. If using the server product delivery mode, the problem could be largely resolved. The application sends the purchased items to server;sever deliver the item to application after checking credentials. There are some corner cases I still don't know how to resolve, basically to handle the case when the whole flow is interrupted, which depeneds on the implementation of IAP. Still not 100% sure yet.
Could you keep a record on the phone about which achievements have been bought by particular users, and then check which user is on and either enable or disable the purchased content - you'd have to have a means of keeping track of different players progress (I can see potential problems where a user might not be logged in to GC, etc etc). I haven't done this yet, tho I'm planning it for my next game.
Related
Let’s assume we have a game with virtual Coins. The game comes with 10 coins from App Store. There is a possibility to purchase coins 1,3,5,10,100… with different prices. The user spends the Coins during the game.
Questions:
Where to store the amount of Coins?
How to prevent using preloaded coins after re-installing the application?
If we need to store the coins on external server, what device identifier should we use? Is it identifierForVendor? If so, uninstalling the application will change the identifier.
Does user expect to have the same Coins on another device? If so, how to handle this?
I think the best solution for this scenario is the in-game account + iCloud:
Have the user profile saved as a plist, for example, secure it to prevent manipulation, and sync it to the iCloud.
Force the iCloud sync each time the app starts.
No need for this as you identify the user by his in-game and iCloud account.
Here I'd say the user would expect the same coins on another device as long as he uses the same profile name and the iCloud account.
I can recommend you the iOS5 by tutorials by Ray Wanderlich if you want to learn iCloud programming.
I'm happy to give you some more detailed info if you ask more detailed questions in the comments.
I'm sorry to say that according to Apple's In-App Purchase Guidelines...
"You may not offer items that represent intermediary currency because
it is important that users know the specific good or service that they
are buying."
https://developer.apple.com/in-app-purchase/In-App-Purchase-Guidelines.pdf
I am building a game which uses achievements currently.
Let's imagine the following situation:
The user starts the app the first time, does not sign in to GameCenter and gets a few achievements. But now he decides to use GameCenter and signs in some time later.
What happens to the gained achievements? Will they be sent to the GameCenter servers later on or do I need to program a check-for-gained-achievements method manually? What did you do?
Thanks for your help!
I stored the data locally in a plist and submit when they login.
In iOS 5 or newer iOS, you have another option to submit offline the achievements and scores when users are not logon to Game Center. This utility behaves as a local cache when users are offline, and it will submit the achievements and scores to Game Center next time the gamers logon to Game Center.
Here is the link a similar question to yours and the answer:
Offline Game Center iOS Achievements
Cheers.
I'm about to add highscore support to my mobile game and I have a basic understanding problem with leaderboard services like OpenFeint or Apples Game Center:
Suppose I'm logged in to OpenFeint and/or Game Center with my account. Then a pal of mine wants to play, I hand him my device and he gets the best score ever. Is there any way he can get his score listed under his name now? My understanding is that he can't, because when the game is over the score is saved, and it is automatically saved for the current account, which happens to be mine at that moment. Tough luck.
This would mean that if I play the game with my pal in turns we would constantly have to log in and out from both services after each game to get it right in the case that one of us gets a highscore. That seems a bit awkward...
Do I overlook something or is this just the way it works? Or do I have to take care for this situation as a developer? Or do the OpenFeint/GameKit SDKs handle this automatically somehow?
I don't know about Open Feint, but at least for Game Center I think the answer to your question is: Yes, that's just the way it works. Even if you know the Game Center id's for both you and your friend, you don't have the ability to save stats for anyone but the logged in game center player.
It does seems possible that they could have supported this use case, to allow more than one player to be "signed in" on a given device, and then the game could just present a "PlayerA", "PlayerB" button to choose who's playing, instead of having to run the Game Center app to do the switch. But I imagine this use case wasn't a super high priority. (They'd rather have each of you playing on your own devices. And in fact some services like ScoreLoop keep things simple by enforcing a single player per device, period.)
imagine there is no internet connection when user is playing. The score cannot be submitted to game center. However I save the highscore on the phone using NSUserDefaults too.
So when the user plays next time and is connected to game center should I sync this score he achieved playing "offline"?
Is that a good practice?
Per the Apple Game Center docs, the answer is YES.
Make Sure Your Game Sends Data Again After a Network Failure
When you implement leaderboards or achievements, your game reports a
player’s scores or achievement progress to Game Center. However,
networking is never perfectly reliable. If a networking error occurs,
your game should save the Game Kit object and retry the action again
at a later time. Both the GKScore and GKAchievement classes support
the NSCoding protocol, so your game can archive those objects when it
moves into the background.
Set up a cache that keeps your score data (I use NSUserDefaults) to preserve data between sessions, and every so often (like, each time the user enters the app) test to see if Game Center is reachable, and if so, upload your cached scores. Let me know if you need any code - this post is pretty old, so I won't be surprised if no one ever answers :)
Also per the Apple docs for iOS 5.0 and later network error related issues are handled by a background reporting task so the developer does not need to write anything to handle this if not supporting previous iOS versions.
(from GKScore Class Reference for method reportScoreWithCompletionHandler:)
If the error is a network error and your game is running on iOS 4.3 or earlier, your game should periodically attempt to report the progress until the score is successfully reported. On iOS 5.0 and later, the background reporting task automatically handles network errors on your game’s behalf.
I am not sure what is supposed to happen if no one is logged into Game Center at all though (no network related/ submission issues) when a high score is achieved and then someone logs in later. In that case no GKScore object can even be created because there is no authenticated player and so there is no way to know who actually achieved the score whenever the next person logs into Game Center. Seems handling logged in (even without a network connection temporarily) is best practice but if no one is logged in at all and a high score is gained then it's just tough luck because it is not known who earned it, other than saving it as a device high score. If anyone handles that case then please tell.
Good question.
In my point of view, if a user is offline and is still playing, the score he/she scores should be saved locally. And when he/she again appears online, the offline score shouldn't be submitted online. Because if offline score is submitted, the purpose of making the game online is defeated.
I'm more than halfway through development of my first iPhone game and I'm currently implementing Game Center features for devices that support it. I have successfully added leaderboard functionality, but have some questions on how to present the Game Center features to the user.
Should Game Center be on and active when the user first runs the app?
Or should Leaderboards and autosubmitting highscores be an option the user have to turn on?
Right now I only submit the score when the user gets a highscore to keep data transfers to a minimum. I just want to make sure the experience is as hassle-free as possible for both Game Center users and people who don't care about highscore/achievements.
I would love to hear from other developers how you chose to present these features!
I'm personally activating the Game Center immediately. If the user has opted in by logging in through Game Center application (or another game), why bug him? Turning off Game Center system-wide is easy. I'm also submitting leaderboard scores, since that allows me to see how many players (or at least Game Center users) enjoy playing the game continuously.
I don't think majority of users that are logged into Game Center would actually want choice. For comparison, OpenFeint provides the choice, but I find that annoying.
What about collecting all the data and only sending it when the users sends the application to the background or terminates it?
From my personal experience I like the Game Center Integration as intrusively as possible. A short notice while game boots and/or a small banner on the highscore table should avoid to much distraction away from your game experience.