iPhone : camera autofocus observer?

Question

I would like to know if it's possible to receive notification about autofocus inside an iPhone application?

I.E, does it exist a way to be notified when autofocus starts, ends, if it has succeed or failed... ?

If so, what is this notification name ?

Answer 1

I find the solution for my case to find when autofocus starts / ends. It's simply dealing with KVO (Key-Value Observing).

In my UIViewController:

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

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

    (...)   
}

// unregister observer
- (void)viewWillDisappear:(BOOL)animated{
    AVCaptureDevice *camDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    [camDevice removeObserver:self forKeyPath:@"adjustingFocus"];

    (...)
}

Documentation:

• Key-Value Observing programming guide
• NSKeyValueObserving protocol