kvo on viewcontroller

kvo.m

// view controller.h

#import <UIKit/UIKit.h>
#import "Item.h"

@interface ViewController : UIViewController 

@property (nonatomic, strong) NSString *myVal;

@end


// view controller.m 
#import "ViewController.h"

static void *context1 = &context1;
static void *context2 = &context2;


@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    [self setValue:@"some string" forKeyPath:@"myVal"];
    [self addObserver:self forKeyPath:@"myVal" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:context1];
    [self addObserver:self forKeyPath:@"myVal" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:context2];
    [self setValue:@"some string else" forKeyPath:@"myVal"];
}


-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{
    
    if(context == context1){
        if ([keyPath isEqualToString:@"myVal"]) {
            NSLog(@"The name of the child was changed.");
            NSLog(@"%@", change);
        }
    }
    
    if(context == context2){
        if ([keyPath isEqualToString:@"myVal"]) {
            NSLog(@"The name of the child was changed.");
            NSLog(@"%@", change);
        }
    }
}

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


@end