2.设置扫描控制器，实现扫描功能

 QRReaderViewController.m文件
  #import "QRReaderViewController.h"
  #import <AVFoundation/AVFoundation.h>
  #import <objc/runtime.h>

  @interface QRReaderViewController() <AVCaptureMetadataOutputObjectsDelegate,
   UINavigationControllerDelegate, UIImagePickerControllerDelegate>

  @property (strong,nonatomic)AVCaptureSession *session;
  @property (strong,nonatomic)AVCaptureVideoPreviewLayer *previewLayer;
  @property (strong, nonatomic) UILabel *infoLabel;
  @property (nonatomic, strong) UIImageView *scanLineImageV;
  @property (nonatomic, strong) NSTimer *scanLineTimer;
  @end

 @implementation QRReaderViewController
 - (void)viewDidLoad {
[super viewDidLoad];

self.view.backgroundColor = [UIColor blackColor];
 //    1.初始化扫描框
  // 这是自己画的一个框框，省略--代码。
[self isScan];
//    2.判断有无摄像头
// 主要实现扫描功能
[self isOnorOffCamera];
}

#pragma mark 2.判断 有无摄像头
- (void)isOnorOffCamera{

  AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
NSError *error = nil;
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];
if (error) {
    input = nil;
    UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"提示" message:@"请在设置-隐私-中打开相机权限" preferredStyle:UIAlertControllerStyleAlert];
    
    UIAlertAction *confirm = [UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {
        [self.navigationController popToRootViewControllerAnimated:YES];
    }];
    
    [alert addAction:confirm];
    [self presentViewController:alert animated:YES completion:nil];
    
}else{
    //       3. 设置扫描功能
    [self initViewAndSubViews];
}

}
#pragma mark 3.设置扫描功能
- (void)initViewAndSubViews {

CGRect scaneBounds = [[UIScreen mainScreen] bounds];
self.view.frame = scaneBounds;

CGRect viewFrame = self.view.frame;
CGSize viewSize = CGSizeMake(viewFrame.size.width - 80, viewFrame.size.width - 80);
        

// 1 实例化摄像头设备
AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];

// 2 设置输入

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

// 3 设置输出
AVCaptureMetadataOutput *outPut = [[AVCaptureMetadataOutput alloc] init];
CGRect scanCrop =
CGRectMake((viewFrame.size.width - viewSize.width)/2,
           (viewFrame.size.height - viewSize.height)/2,
           viewSize.width,
           viewSize.height);
//设置扫描范围
outPut.rectOfInterest =
CGRectMake(scanCrop.origin.y/viewFrame.size.height,
           scanCrop.origin.x/viewFrame.size.width,
           scanCrop.size.height/viewFrame.size.height,
           scanCrop.size.width/viewFrame.size.width
           );

// 4 设置输出的代理

[outPut setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];

// 5 拍摄会话
AVCaptureSession *session = [[AVCaptureSession alloc]init];
session.sessionPreset = AVCaptureSessionPreset640x480;
// 添加session的输入和输出
[session addInput:input];
[session addOutput:outPut];
// 6 设置输出的格式
[outPut setMetadataObjectTypes:@[AVMetadataObjectTypeQRCode]];

// 7 设置预览图层(用来让用户能够看到扫描情况)
AVCaptureVideoPreviewLayer *preview = [AVCaptureVideoPreviewLayer layerWithSession:session];

// 7.1 设置preview图层的属性
[preview setVideoGravity:AVLayerVideoGravityResizeAspectFill];
// 7.2设置preview图层的大小

[preview setFrame:self.view.bounds];
//7.3将图层添加到视图的图层
[self.view.layer insertSublayer:preview atIndex:0];
self.previewLayer = preview;

self.session = session;

}


 - (void)viewWillAppear:(BOOL)animated {

[super viewWillAppear:animated];

//6.启动会话
[self.session startRunning];
 }