Simple KVO example

Question

I am trying to do simple KVO example, but I am having problems.

This is my *.m file:

#import "KVO_ViewController.h"  @interface KVO_ViewController ()  @property NSUInteger number;  @end  @implementation KVO_ViewController  - (void)viewDidLoad {     [super viewDidLoad];     // Do any additional setup after loading the view, typically from a nib.      [self addObserver:self forKeyPath:@"number" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil]; }  - (void)didReceiveMemoryWarning {     [super didReceiveMemoryWarning];     // Dispose of any resources that can be recreated. }  - (IBAction)incNumber:(id)sender {     _number++;     NSLog(@"%d", _number); }  -(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {     NSLog(@"From KVO");      if([keyPath isEqualToString:@"number"])     {         id oldC = [change objectForKey:NSKeyValueChangeOldKey];         id newC = [change objectForKey:NSKeyValueChangeNewKey];          NSLog(@"%@ %@", oldC, newC);     } }  @end 

Note: I have a button which when clicked it will increment the number property.
I want to be notified when number property is changed.

The code is not working and I can not figure it why.

Answer 1

KVO works with setter and getter and in incNumber you are directly accessing iVar so instead of that use self.number

- (IBAction)incNumber:(id)sender {     self.number++;     NSLog(@"%d", self.number); }