Cocoa Design Patterns Adopt and interoperate with Cocoa design patterns in your Swift apps. TopicsCommon PatternsUsing Key-Value Observing in SwiftUsing Delegates to Customize Object BehaviorManaging a Shared Resource Using a SingletonAbout Imported Cocoa Error ParametersHandling Cocoa Errors in Swift See AlsoLanguage Interoperability with Objective-C and CObjective-C and C Code CustomizationMigrating Your Objective-C Code to SwiftHandling Dynamically Typed Methods and Objects in SwiftUsing Objective-C Runtime Features in SwiftImported C and Objective-C APIsCalling Objective-C APIs Asynchronously