GKLeaderboard Class Reference

Inherits from	NSObject
Conforms to	NSObject (NSObject)
Framework	/System/Library/Frameworks/GameKit.framework
Availability	Available in iOS 4.1 and later.
Companion guide	Game Center Programming Guide
Declared in	GKLeaderboard.h
Related sample code	GKTapper

Overview

A GKLeaderboard object is used to read data from a leaderboard stored on Game Center. Your game uses GKLeaderboard objects when it wants to retrieve localized information about a specific leaderboard or to retrieve scores from a leaderboard. Typically, you do this when you want the data needed to implement your own custom leaderboard user interface.

During the development process, you create the leaderboards for your game on iTunes Connect.

To retrieve information about the available leaderboards, use the loadLeaderboardsWithCompletionHandler: class method.

To request score data from Game Center, your game allocates and initializes a GKLeaderboard object, configures its search properties, and then calls the object’s loadScoresWithCompletionHandler: method. Game Kit retrieves the score data from Game Center and calls your completion handler.

The search properties are used to filter the score data returned to your game:

The category property allows you to choose which leaderboard on iTunes Connect is searched.
The playerScope property allows you to restrict the search to a local player’s friends. Optionally, you can also explicitly initialize a leaderboard object to search for scores for a specific group of players.
The timeScope property allows you to filter based on when the score was earned.
The range property allows you to pick scores within a specific range. For example, the range [1,10] returns the best ten scores.

The algorithm used by the GKLeaderboard object is as follows:

Start with the set of all possible scores.
Discard any scores that do not match the playerScope, timeScope and category properties.
For each player, keep the best score that player has earned and discard the rest.
Sort the scores from best to worst.
Use the range property to determine which scores are returned.

Tasks

Determining the Available Leaderboards to Display

Initialization

Customizing the Leaderboard Request

Retrieving High Scores

Changing a Local Player’s Default Leaderboard

Retrieving Group Information

Properties

groupIdentifier

The identifier for the group the leaderboard is part of.

@property(nonatomic, retain) NSString *groupIdentifier

Discussion

If your game was configured to be part of a group in iTunes Connect, this property holds the identifier you assigned to the group.

Availability

Available in iOS 6.0 and later.

Declared In

GKLeaderboard.h

loading

A Boolean value that indicates whether the leaderboard object is retrieving scores. (read-only)

@property(readonly, getter=isLoading) BOOL loading

Discussion

The value of the loading property is YES if the leaderboard object has any pending requests for scores.

Availability

Available in iOS 4.1 and later.

Declared In

GKLeaderboard.h

localPlayerScore

The score earned by the local player. (read-only)

@property(nonatomic, readonly, retain) GKScore *localPlayerScore

Discussion

This property is invalid until a call to loadScoresWithCompletionHandler: is completed. Afterward, it contains a score object representing the local player’s score on the leaderboard given the filters you applied to the query.

Availability

Available in iOS 4.1 and later.

Related Sample Code

GKTapper

Declared In

GKLeaderboard.h

maxRange

The size of the leaderboard. (read-only)

@property(nonatomic, readonly, assign) NSUInteger maxRange

Discussion

This property is invalid until a call to loadScoresWithCompletionHandler: is completed. Afterward, it contains the total number of entries available to return to your game given the filters you applied to the query.

Availability

Available in iOS 4.1 and later.

Declared In

GKLeaderboard.h

playerScope

A filter used to restrict the search to a subset of the players on Game Center.

@property(nonatomic, assign) GKLeaderboardPlayerScope playerScope

Discussion

The playerScope property is ignored if the leaderboard request was initialized using the initWithPlayerIDs: method. Otherwise, the playerScope property determines which players are included in the request for high scores. The default is GKLeaderboardPlayerScopeGlobal. See Leaderboard Player Scope for more information.

Availability

Available in iOS 4.1 and later.

Declared In

GKLeaderboard.h

range

The numerical score rankings to return from the search.

@property(nonatomic, assign) NSRange range

Discussion

The range property is ignored if the leaderboard request was initialized using the initWithPlayerIDs: method. Otherwise, the range property is used to filter which scores are returned to your game. For example, if you specified a range of [1,10], after the search is complete, your game receives the best ten scores. The default range is [1,25].

The minimum index is 1. The maximum length is 100.

Availability

Available in iOS 4.1 and later.

Related Sample Code

GKTapper

Declared In

GKLeaderboard.h

scores

The list of scores returned by the search. (read-only)

@property(nonatomic, readonly, retain) NSArray *scores

Discussion

This property is invalid until a call to loadScoresWithCompletionHandler: is complete. Afterward, it contains the same score objects that were returned to the completion handler.

Availability

Available in iOS 4.1 and later.

Related Sample Code

GKTapper

Declared In

GKLeaderboard.h

timeScope

A filter used to restrict the search to scores that were posted within a specific period of time.

@property(nonatomic, assign) GKLeaderboardTimeScope timeScope

Discussion

This property determines how far back in time to look for scores. The default value is GKLeaderboardTimeScopeAllTime. See Leaderboard Time Scope for more information.

Availability

Available in iOS 4.1 and later.

Related Sample Code

GKTapper

Declared In

GKLeaderboard.h

title

The localized title for the leaderboard. (read-only)

@property(nonatomic, readonly, retain) NSString *title

Discussion

If you initialized a new leaderboard object, this property is invalid until a call to loadScoresWithCompletionHandler: is complete. Afterward, it contains the localized title for the leaderboard identified by the category property.

Availability

Available in iOS 4.1 and later.

Declared In

GKLeaderboard.h

Class Methods

loadLeaderboardsWithCompletionHandler:

Loads the list of leaderboards from Game Center

+ (void)loadLeaderboardsWithCompletionHandler:(void (^)(NSArray *leaderboards, NSError *error))completionHandler

Parameters

completionHandler

A block that is called when the categories have been retrieved from the server.

The block receives the following parameters:

leaderboards: An array of GKLeaderboard objects that provides the leaderboards for your game. If an error occurred, this value may be non-nil. In this case, the array holds whatever data Game Kit was able to download before the error occurred.
error: If an error occurred, this error object describes the error. If the operation completed successfully, the value is nil.

Discussion

Use this class method to retrieve the list of leaderboards you configured on iTunes Connect. Use the properties of each leaderboard object, especially the category and title properties, to learn more about the leaderboard.

When this method is called, it creates a new background task to handle the request. The method then returns control to your game. Later, when the task is complete, Game Kit calls your completion handler. Keep in mind that the completion handler may be called on a thread other than the one originally used to invoke the method. This means that the code in your block needs to be thread-safe.

Availability

Available in iOS 6.0 and later.

Declared In

GKLeaderboard.h

setDefaultLeaderboard:withCompletionHandler:

Sets the default leaderboard for the local player.

+ (void)setDefaultLeaderboard:(NSString *)categoryID withCompletionHandler:(void (^)(NSError *error))completionHandler

Parameters

categoryID

The named leaderboard that should be the new default leaderboard for the local player.

completionHandler

A block to be called after the scores are retrieved from the server.

The block receives the following parameter:

error: If an error occurred, this error object describes the error. If the operation was completed successfully, the value is nil.

Discussion

The default leaderboard is used whenever your game uses a GKScore object to report a score to Game Center without explicitly setting the score object’s category property. The default leaderboard is normally set in iTunes Connect. However, your game can use this class method to override the default leaderboard that appears for the local player. This information is stored for each player on Game Center.

If an error occurs and was a network error, your game should periodically resend the request until it completes.

Availability

Available in iOS 5.0 and later.

Declared In

GKLeaderboard.h

Instance Methods

init

Initializes a default leaderboard request.

- (id)init

Return Value

An initialized leaderboard request.

Discussion

A leaderboard object initialized with this method uses the playerScope, timeScope, and range properties to search Game Center for scores.

Availability

Available in iOS 4.1 and later.

Declared In

GKLeaderboard.h

initWithPlayerIDs:

Initializes a leaderboard request to retrieve the scores of a specific group of players.

- (id)initWithPlayerIDs:(NSArray *)playerIDs

Parameters

playerIDs: An array of NSString objects that holds the player identifier strings of the players to retrieve.

Return Value

An initialized leaderboard request.

Discussion

A leaderboard object initialized with this method ignores the playerScope and range properties. Instead, it retrieves scores for the specific list of players whose identifiers are included in the playerIDs parameter.

Availability

Available in iOS 4.1 and later.

Declared In

GKLeaderboard.h

loadScoresWithCompletionHandler:

Retrieves a set of scores from Game Center.

- (void)loadScoresWithCompletionHandler:(void (^)(NSArray *scores, NSError *error))completionHandler

Parameters

completionHandler

A block to be called after the scores are retrieved from the server.

The block receives the following parameters:

scores: An array of score objects that hold the requested scores. If an error occurred, this value may be non-nil. In this case, the array holds whatever score data could be retrieved from Game Center before the error occurred.
error: If an error occurred, this error object describes the error. If the operation was completed successfully, the value is nil.

Discussion

You can call this method multiple times; each call represents a different query against the scores stored on Game Center. If you post multiple load operations using the same leaderboard object, any properties that are updated by loading scores reflect the last query that completed. The order that achievement queries are processed is arbitrary.

Availability

Available in iOS 4.1 and later.

Related Sample Code

GKTapper

Declared In

GKLeaderboard.h

Constants

Leaderboard Time Scope

The period of time to which a player’s best score is restricted.

enum {
   GKLeaderboardTimeScopeToday = 0,
   GKLeaderboardTimeScopeWeek,
   GKLeaderboardTimeScopeAllTime
};
typedef NSInteger GKLeaderboardTimeScope;

Constants

GKLeaderboardTimeScopeToday

Each player is restricted to scores recorded in the past 24 hours.

Available in iOS 4.1 and later.

Declared in GKLeaderboard.h.

GKLeaderboardTimeScopeWeek

Each player is restricted to scores recorded in the past week.

Available in iOS 4.1 and later.

Declared in GKLeaderboard.h.

GKLeaderboardTimeScopeAllTime

Each player’s best score is returned.

Available in iOS 4.1 and later.

Declared in GKLeaderboard.h.

Availability

Available in iOS 4.1 and later.

Declared In

GKLeaderboard.h

Leaderboard Player Scope

The scope of players to be searched for scores.

enum {
   GKLeaderboardPlayerScopeGlobal = 0,
   GKLeaderboardPlayerScopeFriendsOnly
};
typedef NSInteger GKLeaderboardPlayerScope;

Constants

GKLeaderboardPlayerScopeGlobal

All players on Game Center should be considered when generating the list of scores.

Available in iOS 4.1 and later.

Declared in GKLeaderboard.h.

GKLeaderboardPlayerScopeFriendsOnly

Only friends of the local player should be considered when generating the list of scores.

Available in iOS 4.1 and later.

Declared in GKLeaderboard.h.

Availability

Available in iOS 4.1 and later.

Declared In

GKLeaderboard.h

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