objc KVO example

Children.h

//
//  Children.h
//  KVCODemo
//
//  Created by wisaruthk on 3/3/2559 BE.
//  Copyright © 2559 kojo. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface Children : NSObject
@property(nonatomic,strong) NSString *name;
@property(nonatomic) NSUInteger age;
@property(nonatomic,strong) Children *child;
@property(nonatomic,strong) NSMutableArray *siblings;

-(NSUInteger)countOfSiblings;
-(id)objectInSiblingsAtIndex:(NSUInteger)index;
-(void)insertObject:(NSString *)object inSiblingsAtIndex:(NSUInteger)index;
-(void)removeObjectFromSiblingsAtIndex:(NSUInteger)index;
@end

Children.m

//
//  Children.m
//  KVCODemo
//
//  Created by wisaruthk on 3/3/2559 BE.
//  Copyright © 2559 kojo. All rights reserved.
//

#import "Children.h"

@implementation Children
- (instancetype)init
{
    self = [super init];
    if (self) {
        self.name = @"";
        self.age = 0;
        self.siblings = [[NSMutableArray alloc] init];
    }
    return self;
}

+(BOOL)automaticallyNotifiesObserversForKey:(NSString *)key{
    if([key isEqualToString:@"name"]){
        return NO;
    } else {
        return [super automaticallyNotifiesObserversForKey:key];
    }
}

-(NSUInteger)countOfSiblings{
    return self.siblings.count;
}

-(id)objectInSiblingsAtIndex:(NSUInteger)index{
    return [self.siblings objectAtIndex:index];
}

-(void)insertObject:(NSString *)object inSiblingsAtIndex:(NSUInteger)index{
    [self.siblings insertObject:object atIndex:index];
}

-(void)removeObjectFromSiblingsAtIndex:(NSUInteger)index {
    [self.siblings removeObjectAtIndex:index];
}
@end

output.txt

2016-03-03 14:08:41.103 KVCODemo[55658:19378605] George, 15
2016-03-03 14:08:41.104 KVCODemo[55658:19378605] Andrew, 5
2016-03-03 14:08:41.104 KVCODemo[55658:19378605] The name of the FIRST child was changed.
2016-03-03 14:08:41.104 KVCODemo[55658:19378605] {
    kind = 1;
    new = Michael;
    old = George;
}
2016-03-03 14:08:41.105 KVCODemo[55658:19378605] The age of the FIRST child was changed.
2016-03-03 14:08:41.105 KVCODemo[55658:19378605] {
    kind = 1;
    new = 20;
    old = 15;
}
2016-03-03 14:08:41.105 KVCODemo[55658:19378605] The age of the SECOND child was changed.
2016-03-03 14:08:41.105 KVCODemo[55658:19378605] {
    kind = 1;
    new = 45;
    old = 35;
}
2016-03-03 14:08:41.105 KVCODemo[55658:19378605] {
    indexes = "<_NSCachedIndexSet: 0x7fe463d24db0>[number of indexes: 1 (in 1 ranges), indexes: (0)]";
    kind = 2;
    new =     (
        Alex
    );
}
2016-03-03 14:08:41.106 KVCODemo[55658:19378605] {
    indexes = "<_NSCachedIndexSet: 0x7fe463d24e20>[number of indexes: 1 (in 1 ranges), indexes: (1)]";
    kind = 2;
    new =     (
        Bob
    );
}
2016-03-03 14:08:41.106 KVCODemo[55658:19378605] {
    indexes = "<_NSCachedIndexSet: 0x7fe463d24e40>[number of indexes: 1 (in 1 ranges), indexes: (2)]";
    kind = 2;
    new =     (
        Mary
    );
}
2016-03-03 14:08:41.106 KVCODemo[55658:19378605] {
    indexes = "<_NSCachedIndexSet: 0x7fe463d24e20>[number of indexes: 1 (in 1 ranges), indexes: (1)]";
    kind = 3;
    old =     (
        Bob
    );
}

ViewController.m

//
//  ViewController.m
//  KVCODemo
//
//  Created by wisaruthk on 3/3/2559 BE.
//  Copyright © 2559 kojo. All rights reserved.
//

#import "ViewController.h"
// Context is a pointer point to it self.
static void *someContext = &someContext;
static void *child1Context = &child1Context;
static void *child2Context = &child2Context;
@interface ViewController ()
@property(nonatomic,strong) Children *child1;
@property(nonatomic,strong) Children *child2;
@property(nonatomic,strong) Children *child3;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    self.child1 = [[Children alloc] init];
    
//    self.child1.name = @"George";
//    self.child1.age = 15;
    
    // ถ้าคียร์ไม่มีจะ Error
    [self.child1 setValue:@"George" forKey:@"name"];
    [self.child1 setValue:[NSNumber numberWithInteger:15] forKey:@"age"];
    
    NSString *childName  = [self.child1 valueForKey:@"name"];
    NSUInteger childAge = [[self.child1 valueForKey:@"age"] integerValue];
    
    NSLog(@"%@, %d",self.child1.name,self.child1.age);
    
    self.child2 = [[Children alloc] init];
    [self.child2 setValue:@"Mary" forKey:@"name"];
    [self.child2 setValue:[NSNumber numberWithInteger:35] forKey:@"age"];
    self.child2.child = [[Children alloc] init];
    [self.child2 setValue:@"Andrew" forKeyPath:@"child.name"];
    [self.child2 setValue:[NSNumber numberWithInteger:5] forKeyPath:@"child.age"];
    NSLog(@"%@, %d", self.child2.child.name, self.child2.child.age);
}

-(void)viewWillAppear:(BOOL)animated{
    [super viewWillAppear:animated];
    
    [self.child1 addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:child1Context];
    [self.child1 addObserver:self forKeyPath:@"age" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:child1Context];
    
    // Manual Notifications
    [self.child1 willChangeValueForKey:@"name"];
    [self.child1 setValue:@"Michael" forKey:@"name"];
    [self.child1 didChangeValueForKey:@"name"];
    
    // Auto Notifications
    [self.child1 setValue:[NSNumber numberWithInteger:20] forKey:@"age"];
    
    //
    [self.child2 addObserver:self forKeyPath:@"age" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:child2Context];
    
    [self.child2 setValue:[NSNumber numberWithInteger:45] forKey:@"age"];
    
    // Array Notif
    [self.child1 addObserver:self forKeyPath:@"siblings" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];
    [self.child1 insertObject:@"Alex" inSiblingsAtIndex:0];
    [self.child1 insertObject:@"Bob" inSiblingsAtIndex:1];
    [self.child1 insertObject:@"Mary" inSiblingsAtIndex:2];
    [self.child1 removeObjectFromSiblingsAtIndex:1];
}

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context{
    if(context == child1Context){
    if([keyPath isEqualToString:@"name"]){
        NSLog(@"The name of the FIRST child was changed.");
        NSLog(@"%@",change);
    }
    
    if([keyPath isEqualToString:@"age"]){
        NSLog(@"The age of the FIRST child was changed.");
        NSLog(@"%@",change);
    }
    } else if(context == child2Context){
        if ([keyPath isEqualToString:@"age"]) {
            NSLog(@"The age of the SECOND child was changed.");
            NSLog(@"%@", change);
        }
    } else {
        if([keyPath isEqualToString:@"siblings"]){
            NSLog(@"%@",change);
        }
    }
}

-(void)viewWillDisappear:(BOOL)animated{
    [super viewWillDisappear:animated];
    [self.child1 removeObserver:self forKeyPath:@"name"];
    [self.child1 removeObserver:self forKeyPath:@"age"];
    [self.child2 removeObserver:self forKeyPath:@"age"];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end