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Intro to Obj-C Design Patterns or Or how I lear...

harisamin
August 29, 2014

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.

harisamin

August 29, 2014
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  1. Or how I learned to be less bad Intro to

    Obj-C Design Patterns Haris Amin
  2. Design Patterns • Why do we care? • Let’s explore

    two design patterns in Cocoa 1. Notification Center 2. Delegates
  3. Notification Center • Let’s Grab a NotificationCenter ‘instance’ ! •

    Then PUBLISH a specific message (2 ways) [NSNotificationCenter defaultCenter] 1. With content 2. Without Content
  4. Publish Message Without Content • We want to notify that

    something specific ‘happened’ • Method Signature - (void)postNotificationName:(NSString *)notificationName object:(id)notificationSender
  5. 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];
  6. 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}];
  7. 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 // ... }
  8. 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
  9. • 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
  10. Delegates • Very solid pattern • Vigorously multitude of Cocoa

    classes (UITableView, UICollectionView, UIAlterView.. etc.) • You have to define the protocol of the messages you send
  11. A Personal Note… • I consumed delegates without really understanding

    how they work • I used to be scared of trying to implement one myself
  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. 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
  14. 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
  15. 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
  16. 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