使用AVCaptureSession显示相机预览

#import <UIKit/UIKit.h>
#import <AVFoundation/AVFoundation.h>
@interface ViewController : UIViewController
@property (nonatomic,strong) AVCaptureSession * captureSession;
@property (nonatomic,strong) AVCaptureDeviceInput * videoInput;

@end

- (void)viewDidLoad {
    [super viewDidLoad];
    self.captureSession = [[AVCaptureSession alloc] init];
    self.captureSession.sessionPreset = AVCaptureSessionPresetHigh;
    AVCaptureDevice * device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    NSError * error = nil;
    self.videoInput = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];
    if (self.videoInput) {
        [self.captureSession addInput:self.videoInput];
    }else{
        NSLog(@"Input Error:%@",error);
    }
    AVCaptureVideoPreviewLayer * previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:self.captureSession];
    UIView * aView = self.view;
    previewLayer.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height-70);
    [aView.layer addSublayer:previewLayer];
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    [self.captureSession startRunning];
}

- (void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];
    [self.captureSession stopRunning];
}