AIObservable 0.1.1

You want to add pod 'AIObservable', '~> 0.1' similar to the following to your Podfile:

target 'MyApp' do
  pod 'AIObservable', '~> 0.1'
end

Then run a pod install inside your terminal, or from CocoaPods.app.

Alternatively to give it a test run, run the command:

pod try AIObservable

AIObservable 0.1.1

By
Alejandro Isaza
aleph7

The AIObservable class lets you to dispatch events to a list of observers. It's an implementation of the Observer design pattern. You can add and remove observers even within the notification callback and from multiple threads or queues. Observers are similar to delegates but you can have multiple of them.

This implementation has a few advantages over NSNotificationCenter:

You don't need to call removeObserver: on the observer's dealloc, AIObservable uses zeroing weak references.
When the observable is destroyed all observers are automatically removed.
Each observable object keeps its own set of observers. This makes it easier to debug.
I like having an observer protocol for each class that is observable. A protocol allows you to better document each event that the observable class can dispatch and what parameters it has. It also gives meaningul names to the methods. For instance collection:didAddObject:atIndex: as opposed to didAddObject:(NSNotification*)notification.

Example

As an example suppose you have a chat room. The chat room object dispatches obseravable events when messages are added and people join and leave the room.

@class AIMessage;
@class AIUser;
@protocol AIChatRoomObserver;


@interface AIChatRoom : NSObject 

- (void)postMessage:(AIMessage*)message;
// ...

- (void)addObserver:(id<AIChatRoomObserver>)observer;
- (void)removeObserver:(id<AIChatRoomObserver>)observer;

@end


@protocol AIChatRoomObserver

@optional
- (void)chatRoom:(AIChatRoom*)room didGetNewMessage:(AIMessage*)message;
- (void)chatRoom:(AIChatRoom*)room userDidJoin:(AIUser*)user;
- (void)chatRoom:(AIChatRoom*)room userDidLeave:(AIUser*)user;

@end

As you can see everything has a clear intent and the observer methods are self-documenting. Here is the implementation:

#import <AIObservable.h>
#import <NSInvocation+AIConstructors.h>

@interface AIChatRoom ()

// We use composition but you could also use inheritance
@property (nonatomic, strong) AIObservable* observable;

@end


@implementation AIChatRoom

- (void)postMessage:(AIMessage*)message {
    // ...

    // Create an invocation that will be dispatched to every observer
    AIChatRoom* chatRoom = self;
    NSInvocation* invocation = [NSInvocation invocationWithProtocol:@protocol(AIChatRoomObserver)
                                                           selector:@selector(chatRoom:didGetNewMessage:)];
    [invocation setArgument:&chatRoom atIndex:2];
    [invocation setArgument:&message atIndex:3];
    [self.observable notifyObservers:invocation];
}

- (void)addObserver:(id<AIChatRoomObserver>)observer {
    [self.observable addObserver:observer];
}

- (void)removeObserver:(id<AIChatRoomObserver>)observer {
    [self.observable removeObserver:observer];
}

@end

Installation

Copy the source files to your project or add pod 'AIObservable' to your Podfile.