//1.创建捕捉会话
AVCaptureSession *session = [[AVCaptureSession alloc]init];
self.session = session;
//2. 添加输入设备
AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
AVCaptureDeviceInput *dinput = [AVCaptureDeviceInput deviceInputWithDevice:device error:nil];
[session addInput:dinput];

// 3. 添加输出设备

AVCaptureMetadataOutput *metadataOutput = [[AVCaptureMetadataOutput alloc  ]init];
//3.1这里实在主线程中设置的代理来获取结果实际上要做实际的考虑
[metadataOutput setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
   [session addOutput:metadataOutput];
//3.2  添加到seesion 后才能添加输出的类型
[metadataOutput setMetadataObjectTypes:@[AVMetadataObjectTypeQRCode]];

 //4.添加输出图层
AVCaptureVideoPreviewLayer *preiewLayer =[AVCaptureVideoPreviewLayer layerWithSession:session];
preiewLayer.frame =self.view.bounds;
self.layer = preiewLayer;
[self.view.layer addSublayer:preiewLayer];
// 5开始扫描
[session startRunning];

pragma marke 扫描的代理方法 实现这个代理方法，在这里面获取扫描的结果

• (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection{
  if(metadataObjects.count >0){
  NSLog(@"扫描到二维码");
  // 获取扫描结果
  AVMetadataMachineReadableCodeObject *object = [metadataObjects lastObject];
  NSLog(@"%@",object.stringValue);
  // 停止扫描
  [self.session stopRunning];
  [self.layer removeFromSuperlayer];
  }else{
  NSLog(@"没有扫描到数据");
  }
  }