GKNSPredicateRule

The GKNSPredicateRule class is a specialized subclass of the GKRule class (which represents rules to be used by GKRuleSystem objects). Custom subclasses of GKNSPredicateRule use an NSPredicate object to evaluate a rule, rather than requiring custom logic for evaluation as is the case with custom GKRule subclasses.

For more information about rules and rule systems, read Rule Systems in GameplayKit Programming Guide.

GameplayKit evaluates rules in the context of a GKRuleSystem object, so custom rule classes should be functional—that is, they generally should not carry independent state that affects their predicate or action.

Override the performActionWithSystem: method to perform whatever actions should result when your rule is satisfied (that is, when its predicate property evaluates to true in the context of the provided rule system).

• Use the GKRule method ruleWithPredicate:assertingFact:grade: or ruleWithPredicate:retractingFact:grade: to create a rule that uses an NSPredicate object for evaluation and whose action asserts or retracts a fact in the containing rule system.

• Use the GKRule method ruleWithBlockPredicate:action: method to quickly create a rule whose custom logic is contained in block objects.