var session: AVCaptureSession?;
var previewLayer: AVCaptureVideoPreviewLayer?;  

func readQRCode() {//1.获取摄像头设备var device:AVCaptureDevice = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo);//2.设置输入var error: NSError?;var input: AVCaptureDeviceInput = AVCaptureDeviceInput.deviceInputWithDevice(device, error: &error) as AVCaptureDeviceInput;if (error != nil) {println("没有摄像头\(error?.localizedDescription)");return;}// 3. 设置输出(Metadata元数据)var output: AVCaptureMetadataOutput = AVCaptureMetadataOutput();// 3.1 设置输出的代理// 说明：使用主线程队列，相应比较同步，使用其他队列，相应不同步，容易让用户产生不好的体验
        output.setMetadataObjectsDelegate(self, queue: dispatch_get_main_queue());// 4. 拍摄会话var session1: AVCaptureSession = AVCaptureSession();session1.addInput(input);session1.addOutput(output);// 4.1 设置输出的格式// 提示：一定要先设置会话的输出为output之后，再指定输出的元数据类型！output.metadataObjectTypes = [AVMetadataObjectTypeQRCode];// 5. 设置预览图层（用来让用户能够看到扫描情况）var preview: AVCaptureVideoPreviewLayer = AVCaptureVideoPreviewLayer.layerWithSession(session1) as AVCaptureVideoPreviewLayer;// 5.1 设置preview图层的属性preview.videoGravity = AVLayerVideoGravityResizeAspectFill;// 5.2 设置preview图层的大小preview.frame = self.view.bounds;// 5.3 将图层添加到视图的图层self.view.layer.insertSublayer(preview, atIndex: 0);self.previewLayer = preview;// 6. 启动会话
        session1.startRunning();self.session = session1;}func captureOutput(captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [AnyObject]!, fromConnection connection: AVCaptureConnection!) {// 会频繁的扫描，调用代理方法// 1. 如果扫描完成，停止会话self.session?.stopRunning();// 2. 删除预览图层self.previewLayer?.removeFromSuperlayer();println(metadataObjects);// 3. 设置界面显示扫描结果if (metadataObjects.count > 0) {var obj:AVMetadataMachineReadableCodeObject = metadataObjects[0] as AVMetadataMachineReadableCodeObject;// 提示：如果需要对url或者名片等信息进行扫描，可以在此进行扩展！println("结果如下：" + obj.stringValue);}}