GKGameCenterViewControllerState.challenges The view controller should present a list of challenges. Declarationcase challenges See AlsoStatesGKGameCenterViewControllerState.defaultGKGameCenterViewControllerState.leaderboardsGKGameCenterViewControllerState.achievementsGKGameCenterViewControllerState.localPlayerProfileGKGameCenterViewControllerState.dashboardGKGameCenterViewControllerState.localPlayerFriendsList