如何使用Swift 3获取扫描条形码照片？

import UIKit
import AVFoundation

class BarcodeScannerViewController: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
    var captureSession: AVCaptureSession!
    var previewLayer: AVCaptureVideoPreviewLayer!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建捕捉会话
        captureSession = AVCaptureSession()
        
        // 获取后置摄像头设备
        guard let videoCaptureDevice = AVCaptureDevice.default(for: .video) else { return }
        
        // 创建输入流
        guard let videoInput = try? AVCaptureDeviceInput(device: videoCaptureDevice) else { return }
        
        // 将输入流添加到会话
        if captureSession.canAddInput(videoInput) {
            captureSession.addInput(videoInput)
        } else {
            print("无法将输入流添加到会话")
            return
        }
        
        // 创建输出流
        let metadataOutput = AVCaptureMetadataOutput()
        
        // 将输出流添加到会话
        if captureSession.canAddOutput(metadataOutput) {
            captureSession.addOutput(metadataOutput)
            
            // 设置元数据类型为条形码
            metadataOutput.metadataObjectTypes = [.ean8, .ean13, .pdf417, .qr]
            
            // 设置代理，在扫描到条形码时触发代理方法
            metadataOutput.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
        } else {
            print("无法将输出流添加到会话")
            return
        }
        
        // 创建预览图层并将其添加到视图上
        previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
        previewLayer.frame = view.layer.bounds
        previewLayer.videoGravity = .resizeAspectFill
        view.layer.addSublayer(previewLayer)
        
        // 启动会话
        captureSession.startRunning()
    }
    
    // 扫描到条形码时触发的代理方法
    func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {
        // 检查是否扫描到了条形码
        if let metadataObject = metadataObjects.first {
            guard let readableObject = metadataObject as? AVMetadataMachineReadableCodeObject else { return }
            guard let stringValue = readableObject.stringValue else { return }
            
            // 停止会话
            captureSession.stopRunning()
            
            // 处理扫描到的条形码数据
            print("扫描到的条形码：\(stringValue)")
        }
    }
}