How is it right to hand a line on the iPhone screen?

[meriah]

I'm trying to get the counter. The point is, some line should be placed on a smartphone screen at a speed of personnel, that is, 20 to 30 times a second.

Realizing this beauty by transferring staff. Somehow:

CODE UPDATE (1700; 01.07.2016 ICN)

//.h file
#import <UIKit/UIKit.h>
int N = 0; //Глобальная переменная для подсчета кадров
@interface ViewController : UIViewController

@property (weak, nonatomic) IBOutlet UILabel *Label; //строка на экране
@end
//.m file

#import "ViewController.h"

#import <AVFoundation/AVFoundation.h>

@interface ViewController ()

@property (weak, nonatomic) IBOutlet UIImageView *imageView;
@end
@implementation ViewController
{

AVCaptureSession *session;
}

- (void)viewDidLoad {

[super viewDidLoad];

[self setupCaptureSession];
}
- (void)setupCaptureSession    //инициализация сессии съемки
{

    NSError *error = nil;          
    session = [[AVCaptureSession alloc] init];          

    session.sessionPreset = AVCaptureSessionPresetMedium;

    AVCaptureDevice *device = [AVCaptureDevice                                       
                               defaultDeviceWithMediaType:AVMediaTypeVideo];       


    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&amp;error];

    if (!input) {                
    }

    [session addInput:input];

    AVCaptureVideoDataOutput *output = [[AVCaptureVideoDataOutput alloc] init];

    dispatch_queue_t queue = dispatch_queue_create("myQueue", NULL); //создание очереди кадров            
    [output setSampleBufferDelegate:self queue:queue];// создание буфера сэмплов и добавление очереди 
     [session addOutput:output];
     [session startRunning];

}

//В методе строкой ниже, осуществляется передача кадров с камеры в буфер

(void)captureOutput:(AVCaptureOutput *)captureOutput

didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer
   fromConnection:(AVCaptureConnection *)connection

{

NSString *text = [NSString stringWithFormat: @"N = %d", N]; //to create string with global variable N

self.Label.text = text; //вывести строку на экран айфона

NSLog(text); //распечатать строку в консоль

N++;

}
@end

The gear is working, but it's very slow. The line on the screen shall not be renewed until 10 seconds after the application is launched. Besides, sometimes I start an app, and the line doesn't want to be updated.

Question: Is there a way to better transfer the line on the smartphone screen? How do you do that?

[nishika]

20 to 30 times a second to update the line for the motto. But it's worth checking how often Output:didOutputSampleBuffer: If he's rarely called, you're not gonna do anything. Add that method to the log.

UI try to update this (to be exact from the main flow):

dispatch_async(dispatch_get_main_queue(), ^{
            // Update UI
            self.Label.text = text;
        });