Key-Value Observing adjustingFocus no notification - objective-c

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.