Key-Value Observing adjustingFocus no notification

Question

I'm not familiar with iOS but I'm trying to find when the default, built-in camera application is focusing. To do this I create my own separate Objective-C application and following this answer here [iPhone : camera autofocus observer? but I'm not getting anything from observeValueForKeyPath in the NSLog.

#import "ViewController.h"
#import "AVFoundation/AVCaptureDevice.h"
#import "AVFoundation/AVMediaFormat.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    NSLog(@"viewDidLoad");
}

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

// callback
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    NSLog(@"observeValueForKeyPath");
    if( [keyPath isEqualToString:@"adjustingFocus"] ){
        BOOL adjustingFocus = [ [change objectForKey:NSKeyValueChangeNewKey] isEqualToNumber:[NSNumber numberWithInt:1] ];
        NSLog(@"Is adjusting focus? %@", adjustingFocus ? @"YES" : @"NO" );
        NSLog(@"Change dictionary: %@", change);
    }
    if( [keyPath isEqualToString:@"focusMode"] ){
        AVCaptureFocusMode focusMode = [ [change objectForKey:NSKeyValueChangeNewKey] isEqualToNumber:[NSNumber numberWithInt:1] ];
        NSLog(@"focusMode? %ld", focusMode);
    }
}

// register observer
- (void)viewWillAppear:(BOOL)animated{
    [super viewWillAppear: animated];
    NSLog(@"viewWillAppear");
    AVCaptureDevice *camDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    int flags = NSKeyValueObservingOptionNew;
    [camDevice addObserver:self forKeyPath:@"adjustingFocus" options:flags context:nil];
    [camDevice addObserver:self forKeyPath:@"focusMode" options:flags context:nil];
}

@end

Any help much appreciated.

Answer 1

For anyone who visits this question, the answer is what Bluewings wrote as a comment. I was trying to use KVO to observe one application from another which is not possible since only one lock on a capture device is possible at one time.