iOS AVcapture video preview not working.

@property (weak, nonatomic) IBOutlet UIView *videoPreviewLayer;

#import <UIKit/UIKit.h>
@class AVCaptureVideoPreviewLayer;
@interface ViewController : UIViewController
- (IBAction)imageCapture:(id)sender;
@property (weak, nonatomic) IBOutlet UIView *videoPreviewLayer;

@end

#import "ViewController.h"
#import <AVFoundation/AVFoundation.h>


@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad
{
    AVCaptureSession *session = [[AVCaptureSession alloc] init];
    session.sessionPreset = AVCaptureSessionPresetPhoto;
    AVCaptureDevice *device = [AVCaptureDevice
                               defaultDeviceWithMediaType:AVMediaTypeVideo];
    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:NULL];
    [session addInput:input];
//    dispatch_queue_t queue = dispatch_queue_create("MyQueue", NULL);
//    [output setSampleBufferDelegate:self queue:queue];
    AVCaptureVideoPreviewLayer *preview = [[AVCaptureVideoPreviewLayer alloc] initWithSession:session];
    CALayer *viewLayer = [_videoPreviewLayer layer];
    [viewLayer setMasksToBounds:YES];
    CGRect bounds = [_videoPreviewLayer bounds];
    [preview setFrame:bounds];
//    preview.frame = self.view.frame;
//    [self.view.layer addSublayer:preview];
    [session startRunning];
    [super viewDidLoad];
	// Do any additional setup after loading the view, typically from a nib.
}

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

- (IBAction)imageCapture:(id)sender {
}

- (void)captureOutput:(AVCaptureOutput *) captureOutput
    didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
   // CFShow(sampleBuffer);
}
@end