Intro to Obj-C Design Patterns or Or how I learned to be less bad

Presented at A Swift Start on 08/29/2014:
A one day iOS community conference discussing
the ups and downs of learning iOS. Beginners and pros invited

An intro to two Objc-C/Cocoa design patterns: Notification Center and Delegates. The talk focuses on learning multiple ways to solve the problem while avoiding the 'chainsaw massacre' of one powerful approach over another.

Transcript

1. Or how I learned to be less bad Intro to Obj-C Design Patterns Haris Amin
2. GLIMPSE A fun way to meet new people through Instagram
3. Design Patterns • Why do we care? • Let’s explore two design patterns in Cocoa 1. Notification Center 2. Delegates
4. Notification Center • NSNotificationCenter class • Easiest to learn (IMHO) but also easiest to abuse • Very flexible
5. Notification Center • Let’s Grab a NotificationCenter ‘instance’ ! • Then PUBLISH a specific message (2 ways) [NSNotificationCenter defaultCenter] 1. With content 2. Without Content
6. Publish Message Without Content • We want to notify that something specific ‘happened’ • Method Signature - (void)postNotificationName:(NSString *)notificationName object:(id)notificationSender
7. Publish Message Without Content • E.G. The Video’s current time just updated - (void)postNotificationName:(NSString *)notificationName object:(id)notificationSender [[NSNotificationCenter defaultCenter] postNotificationName:@"TimeUpdated" object:self];
8. Publish Message With Content • E.G. The Video’s current time just updated WITH the actual current time - (void)postNotificationName:(NSString *)notificationName object:(id)notificationSender userInfo:(NSDictionary *)userInfo [[NSNotificationCenter defaultCenter] postNotificationName:@"TimeUpdated" object:self userInfo:@{@"currentTime": 20}];
9. Subscribing to a Message • In our VideoPlayer class we will just subscribe to the NotificationCenter Message - (void)addObserver:(id)notificationObserver selector:(SEL)notificationSelector name:(NSString *)notificationName object:(id)notificationSender [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleTimeUpdate:) name:@"TimeUpdated" object:nil]; - (void)handleTimeUpdate:(NSNotification *)note{ // note.userInfo is the CONTENT we passed // ... }
10. Notification Center… THE GOOD • Really flexible • Don’t have to define any sort of protocol for your messages • You can subscribe and publish messages in any number of places
11. • TOO flexible?! • Don’t have to define any sort of protocol for your messages • You can subscribe and publish messages in any number of of places Notification Center… THE BAD
12. Delegates • Very solid pattern • Vigorously multitude of Cocoa classes (UITableView, UICollectionView, UIAlterView.. etc.) • You have to define the protocol of the messages you send
13. A Personal Note… • I consumed delegates without really understanding how they work • I used to be scared of trying to implement one myself
14. TIME TO GAIN A SUPERPOWER!
15. Delegates • Very solid pattern • Vigorously multitude of Cocoa classes (UITableView, UICollectionView, UIAlterView.. etc.) • You have to define the protocol of the messages you send
16. Define a Delegate Protocol • Very solid pattern • Vigorously multitude of Cocoa classes (UITableView, UICollectionView, UIAlterView.. etc.) • You have to define the protocol of the messages you send
17. Define Protocol @protocol VideoDelegate; ! @interface Video: NSObject ! @property (nonatomic, weak) id<VideoDelegate> delegate; ! @end ! @protocol VideoDelegate <NSObject> @required //... ! @optional -(void)video:(Video *)video updatedTime:(NSUInteger)currentTime; ! @end // end of delegate protocol
18. Delegating Methods in the Protocol • In our Video class, where need be, we will delegate respective messages @implementation Video //.. ! if (self.delegate && [self.delegate respondsToSelector:@selector(video:updatedTime)]) { [self.delegate video:updatedTime]; } //.. @end
19. Implement Protocol #include "Video.h" // needed to include the @delegate protocol info ! @interface VideoPlayer : UIViewController <VideoDelegate> @end ! @implementation VideoPlayer //.. ! -(void)video:(Video *)video updatedTime:(NSUInteger)currentTime{ // HURRAY! We know what the currentTime is :) } ! //.. @end
20. A parting note… with great SUPER power comes great SUPER responsibility!
21. Questions? Cofounder/CO-CTO @itsglimpse @harisamin HARIS AMIN