IOS 监听相机对焦事件

 

来自官方文档：

You can use the adjustingFocus property to determine whether a device is currently focusing. You can observe the property using key-value observing to be notified when a device starts and stops focusing.

 

来自StackoverFlow：

// 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"];

    (...)
}