Feed dog when it's hungry (w/ the help of observers) #objc

Dog.h

//
//  Dog.h
//  Fiddle
//
//  Created by Juho H on 18/02/15.
//  Copyright (c) 2015 Juho Hautala. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface Dog : NSObject

@property int hunger;

- (void)liveAnHour;

@end

Dog.m

//
//  Dog.m
//  Fiddle
//
//  Created by Juho H on 18/02/15.
//  Copyright (c) 2015 Juho Hautala. All rights reserved.
//

#import "Dog.h"

@interface Dog ()

//@property int hunger;

@end

@implementation Dog

- (instancetype)init {
    if (self = [super init]) {
        _hunger = 1;
    }
    
    return self;
}

- (void)liveAnHour {
    // Have to access the magic setter.
    // _hunger will not work here w/ observers.
    self.hunger += 1;
}

@end

main.m

//
//  main.m
//  Fiddle
//
//  Created by Juho H on 18/02/15.
//  Copyright (c) 2015 Juho Hautala. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "Dog.h"
#import "Person.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {

        Person *me = [[Person alloc] init];
        Dog *dog = [[Dog alloc] init];
        
        [dog addObserver:me
              forKeyPath:@"hunger"
                 options:NSKeyValueObservingOptionNew
                 context:nil];

        NSLog(@"Dogs hunger: %@", [dog valueForKey:@"hunger"]);

        [dog liveAnHour];
        NSLog(@"Dogs hunger: %@", [dog valueForKey:@"hunger"]);
        
        [dog liveAnHour];
        NSLog(@"Dogs hunger: %@", [dog valueForKey:@"hunger"]);
        
        [dog liveAnHour];
        NSLog(@"Dogs hunger: %@", [dog valueForKey:@"hunger"]);

        [dog removeObserver:me forKeyPath:@"hunger"];
    }

    return 0;
}

Person.h

//
//  Person.h
//  Fiddle
//
//  Created by Juho H on 18/02/15.
//  Copyright (c) 2015 Juho Hautala. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface Person : NSObject


@end

Person.m

//
//  Person.m
//  Fiddle
//
//  Created by Juho H on 18/02/15.
//  Copyright (c) 2015 Juho Hautala. All rights reserved.
//

#import "Person.h"
#import "Dog.h"

@implementation Person

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    if ([keyPath  isEqual: @"hunger"]) {
        NSNumber *hunger = [object valueForKeyPath:keyPath];
    
        if (3 < hunger.integerValue) {
            [object setHunger:1];
            NSLog(@"Dog fed");
        }
    }
}

@end