Receiptionist patter over KVO

receptionistPattern.m

#import <Foundation/Foundation.h>

typedef void (^ReceptionistTask)(NSString *keyPath, id obj, NSDictionary *change);

@interface Receptionist : NSObject
+ (instancetype)receptionistForObject:(id)obj withKeyPath:(NSString*)keyPath withQueue:(NSOperationQueue*)queue withTask:(ReceptionistTask)task;
@end

@implementation Receptionist {
    id _observerdObj;
    NSString *_observerKeyPath;
    NSOperationQueue *_queue;
    ReceptionistTask _task;
    
}

+ (instancetype)receptionistForObject:(id)obj withKeyPath:(NSString*)keyPath withQueue:(NSOperationQueue*)queue withTask:(ReceptionistTask)task {
    
    Receptionist *receptionist = [Receptionist new];
    
    receptionist->_observerdObj = obj;
    receptionist->_observerKeyPath = keyPath;
    receptionist->_queue = queue;
    receptionist->_task = [task copy];
    
    [obj addObserver:receptionist forKeyPath:keyPath options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:NULL];
    
    return receptionist;
    
}
     
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    
    [_queue addOperationWithBlock:^{
        _task(keyPath, object, change);
    }];
    
}

- (void)dealloc {
    [_observerdObj removeObserver:self];
}

@end