Delegation vs. Notification by Jay Thrash

Jay Thrash (@jaythrash) discussed Delegation and Notification in Cocoa at CocoaHeads Raleigh in April 2012

Transcript

1. Delegation vs. Noti cation Triangle CocoaHeads :: April 2012 Jay Thrash jay.thrash@mac.com @jaythrash
2. Goals for This Talk •Understand the difference between Delegation and Noti cation •Identify when to use one convention over the other
3. Delegates & Noti cations Purpose
4. Purpose • Apps live in an event- driven world • Events are manifested in code as messages • Handle events while remaining architecturally exible • Decouple Communications
5. Purpose • Apps live in an event- driven world • Events are manifested in code as messages • Handle events while remaining architecturally exible • Decouple Communications
6. Noti cations “Spread the word”
7. Noti cations •Communication via third party - NSNoti cationCenter •Multiple objects can react to the same event •Is there anybody out there? Don’t know. Don’t care.
8. Noti cations •Communication via third party - NSNoti cationCenter •Multiple objects can react to the same event •Is there anybody out there? Don’t know. Don’t care.
9. Noti cations // To send a notification NSString *TCHChocolateAvailable = @” TCHChocolateAvailable”; [[NSNotificationCenter defaultCenter] postNotificationName: TCHChocolateAvailable object:self]; // To include a dictionary NSString *TCHProductName = @”TCHProductName”; NSDictionary *msgData = [NSDictionary dictionaryWithObject:@"Snickers" forKey:TCHProductName]; [[NSNotificationCenter defaultCenter] postNotificationName:TCHChocolateAvailable ! ! ! ! ! ! ! ! object:nil ! ! ! ! ! ! ! ! ! ! ! ! userInfo:msgData]; // To receive a notification message [[NSNotificationCenter defaultCenter] addObserver:self ! ! ! selector:@selector(eatChocolate:) ! ! ! name: TCHProductAvailable ! ! ! object:nil]; - (void)eatChocolate:(NSNotification *)notification { NSDictionary *userInfo = [notification userInfo]; NSString *productName = [userInfo objectForKey:TCHProductName]; // ... todo eat candy }
10. Noti cations // To send a notification NSString *TCHChocolateAvailable = @” TCHChocolateAvailable”; [[NSNotificationCenter defaultCenter] postNotificationName: TCHChocolateAvailable object:self]; // To include a dictionary NSString *TCHProductName = @”TCHProductName”; NSDictionary *msgData = [NSDictionary dictionaryWithObject:@"Snickers" forKey:TCHProductName]; [[NSNotificationCenter defaultCenter] postNotificationName:TCHChocolateAvailable ! ! ! ! ! ! ! ! object:nil ! ! ! ! ! ! ! ! ! ! ! ! userInfo:msgData]; // To receive a notification message [[NSNotificationCenter defaultCenter] addObserver:self ! ! ! selector:@selector(eatChocolate:) ! ! ! name: TCHProductAvailable ! ! ! object:nil]; - (void)eatChocolate:(NSNotification *)notification { NSDictionary *userInfo = [notification userInfo]; NSString *productName = [userInfo objectForKey:TCHProductName]; // ... todo eat candy }
11. Noti cations // To send a notification NSString *TCHChocolateAvailable = @” TCHChocolateAvailable”; [[NSNotificationCenter defaultCenter] postNotificationName: TCHChocolateAvailable object:self]; // To include a dictionary NSString *TCHProductName = @”TCHProductName”; NSDictionary *msgData = [NSDictionary dictionaryWithObject:@"Snickers" forKey:TCHProductName]; [[NSNotificationCenter defaultCenter] postNotificationName:TCHChocolateAvailable ! ! ! ! ! ! ! ! object:nil ! ! ! ! ! ! ! ! ! ! ! ! userInfo:msgData]; // To receive a notification message [[NSNotificationCenter defaultCenter] addObserver:self ! ! ! selector:@selector(eatChocolate:) ! ! ! name: TCHProductAvailable ! ! ! object:nil]; - (void)eatChocolate:(NSNotification *)notification { NSDictionary *userInfo = [notification userInfo]; NSString *productName = [userInfo objectForKey:TCHProductName]; // ... todo eat candy }
12. Noti cations // To send a notification NSString *TCHChocolateAvailable = @” TCHChocolateAvailable”; [[NSNotificationCenter defaultCenter] postNotificationName: TCHChocolateAvailable object:self]; // To include a dictionary NSString *TCHProductName = @”TCHProductName”; NSDictionary *msgData = [NSDictionary dictionaryWithObject:@"Snickers" forKey:TCHProductName]; [[NSNotificationCenter defaultCenter] postNotificationName:TCHChocolateAvailable ! ! ! ! ! ! ! ! object:nil ! ! ! ! ! ! ! ! ! ! ! ! userInfo:msgData]; // To receive a notification message [[NSNotificationCenter defaultCenter] addObserver:self ! ! ! selector:@selector(eatChocolate:) ! ! ! name: TCHProductAvailable ! ! ! object:nil]; - (void)eatChocolate:(NSNotification *)notification { NSDictionary *userInfo = [notification userInfo]; NSString *productName = [userInfo objectForKey:TCHProductName]; // ... todo eat candy }
13. Noti cations
14. Noti cations Pros Cons
15. Noti cations •One to many •Very lightweight code requirements •Highly Decoupled •Fire & Forget Pros Cons
16. Noti cations •One to many •Very lightweight code requirements •Highly Decoupled •Fire & Forget •Chaperone Required •No compile-time checks •Manually Managed •Unwanted Feedback •Unknown Delivery Order Pros Cons
17. Delegation “Pass the buck”
18. Delegation del∙e∙gate verb |ˈdel!ˌgāt| To entrust (a task or responsibility) to another person
19. Delegation
20. Delegation •Follow the protocol
21. Delegation •Follow the protocol •id Required
22. Delegation •Follow the protocol •id Required •Delegate vs. DataSource
23. Delegation // Protocol defines the delegate’s requirements @protocol TCHMeetupSpeakerDelegate<NSObject> @optional // ... - (NSString *) meetUp:(TCHMeetup *)meetUp nameForSpeaker; - (BOOL) meetUp:(TCHMeetup *)meetUp willSpeakForPizza:(NSArray *)pizzaToppings; // ... @end // Another class implements the protocol @interface SpeakerController<TCHMeetupDelegate> @property (nonatomic, retain) TCHMeetup *meetUp; @end // Assign the delegate self.meetUp.delegate = self;
24. Delegation // Protocol defines the delegate’s requirements @protocol TCHMeetupSpeakerDelegate<NSObject> @optional // ... - (NSString *) meetUp:(TCHMeetup *)meetUp nameForSpeaker; - (BOOL) meetUp:(TCHMeetup *)meetUp willSpeakForPizza:(NSArray *)pizzaToppings; // ... @end // Another class implements the protocol @interface SpeakerController<TCHMeetupDelegate> @property (nonatomic, retain) TCHMeetup *meetUp; @end // Assign the delegate self.meetUp.delegate = self;
25. Delegation // Protocol defines the delegate’s requirements @protocol TCHMeetupSpeakerDelegate<NSObject> @optional // ... - (NSString *) meetUp:(TCHMeetup *)meetUp nameForSpeaker; - (BOOL) meetUp:(TCHMeetup *)meetUp willSpeakForPizza:(NSArray *)pizzaToppings; // ... @end // Another class implements the protocol @interface SpeakerController<TCHMeetupDelegate> @property (nonatomic, retain) TCHMeetup *meetUp; @end // Assign the delegate self.meetUp.delegate = self;
26. Delegation // Protocol defines the delegate’s requirements @protocol TCHMeetupSpeakerDelegate<NSObject> @optional // ... - (NSString *) meetUp:(TCHMeetup *)meetUp nameForSpeaker; - (BOOL) meetUp:(TCHMeetup *)meetUp willSpeakForPizza:(NSArray *)pizzaToppings; // ... @end // Another class implements the protocol @interface SpeakerController<TCHMeetupDelegate> @property (nonatomic, retain) TCHMeetup *meetUp; @end // Assign the delegate self.meetUp.delegate = self;
27. Delegation // Protocol defines the delegate’s requirements @protocol TCHMeetupSpeakerDelegate<NSObject> @optional // ... - (NSString *) meetUp:(TCHMeetup *)meetUp nameForSpeaker; - (BOOL) meetUp:(TCHMeetup *)meetUp willSpeakForPizza:(NSArray *)pizzaToppings; // ... @end // Another class implements the protocol @interface SpeakerController<TCHMeetupDelegate> @property (nonatomic, retain) TCHMeetup *meetUp; @end // Assign the delegate self.meetUp.delegate = self;
28. Delegation
29. Delegation Pros Cons
30. Delegation •Minimal coupling •Clearly de ned expectations •Easier to debug ow •Return to sender Pros Cons
31. Delegation •Minimal coupling •Clearly de ned expectations •Easier to debug ow •Return to sender •Weak References •Protocols can be code heavy •There can only be one •Bigger commitment Pros Cons
32. Delegation or Noti cation?
33. Delegation or Noti cation?
34. Delegation or Noti cation? Delegation Noti cation
35. •One-to-One •Inform & In uence the sender Delegation or Noti cation? Delegation Noti cation
36. •One-to-One •Inform & In uence the sender •Reach Multiple objects •No Response Necessary Delegation or Noti cation? Delegation Noti cation
37. •One-to-One •Inform & In uence the sender •Reach Multiple objects •No Response Necessary Delegation or Noti cation? Delegation Noti cation
38. •One-to-One •Inform & In uence the sender •Reach Multiple objects •No Response Necessary Delegation or Noti cation? Delegation Noti cation