Ios AVFoundation Camera推出变焦SWIFT

我有一台使用AVFoundation和Swift定制的相机.当相机启动时，它最初是放大的.大约一秒钟后，它会缩小到正常状态.我不确定为什么会发生这种情况，我根本没有修改放大倍数，我也没有改变输入相机.也许我的setUp()函数中有问题.

struct CameraPreview: UIViewRepresentable {
   @EnvironmentObject var cameraModel : CameraViewModel
   var size: CGSize
   
   func makeUIView(context: Context) -> UIView {
       let view = UIView(frame: CGRect(origin: .zero, size: size))
       guard let preview = cameraModel.preview else { return view }

       preview.frame = view.bounds
       preview.videoGravity = .resizeAspectFill
       view.layer.addSublayer(preview)

       DispatchQueue.global(qos: .userInitiated).async {
           if !self.cameraModel.session.isRunning {
               self.cameraModel.session.startRunning()
           }
       }
       
       return view
   }
   
   func updateUIView(_ uiView: UIView, context: Context) { }
}


class CameraViewModel: NSObject, ObservableObject, AVCaptureFileOutputRecordingDelegate, AVCapturePhotoCaptureDelegate {
   @Published var session = AVCaptureSession()
   @Published var alert = false
   @Published var output = AVCaptureMovieFileOutput()
   @Published var preview: AVCaptureVideoPreviewLayer!
   @Published var isRecording: Bool = false
   @Published var recordedURLs: [URL] = []
   @Published var previewURL: URL?
   @Published var showPreview: Bool = false
   @Published var recordedDuration: CGFloat = 0
   @Published var maxDuration: CGFloat = 25
   @Published var capturedImage: UIImage?
   @Published var photoOutput = AVCapturePhotoOutput()
   @Published var flashMode: AVCaptureDevice.TorchMode = .off
   var currentCameraPosition: AVCaptureDevice.Position = .back
   @Published var photoMode: Bool = true
   @Published var isVideoFlashOn: Bool = false
   
   override init() {
       super.init()
       self.checkPermission()
       self.preview = AVCaptureVideoPreviewLayer(session: session)
       self.preview.videoGravity = .resizeAspectFill
   }
   
   func photoOutput(_ output: AVCapturePhotoOutput, didFinishProcessingPhoto photo: AVCapturePhoto, error: Error?) {

   }
   
   func checkPermission(){
       switch AVCaptureDevice.authorizationStatus(for: .video) {
       case .authorized:
           checkAudioPermission()
           return
       case .notDetermined:
           AVCaptureDevice.requestAccess(for: .video) { (status) in
               if status {
                   self.checkAudioPermission()
               }
           }
       case .denied:
           self.alert.toggle()
           return
       default:
           return
       }
   }
   
   func checkAudioPermission() {
       switch AVCaptureDevice.authorizationStatus(for: .audio) {
       case .authorized:
           setUp()
           return
       case .notDetermined:
           AVCaptureDevice.requestAccess(for: .audio) { (audioStatus) in
               if audioStatus {
                   self.setUp()
               }
           }
       case .denied:
           self.alert.toggle()
           return
       default:
           return
       }
   }
   
   func setUp(){
       do {
           self.session.beginConfiguration()
           let cameraDevice = AVCaptureDevice.default(.builtInWideAngleCamera, for: .video, position: .back)
           let videoInput = try AVCaptureDeviceInput(device: cameraDevice!)
           let audioDevice = AVCaptureDevice.default(for: .audio)
           let audioInput = try AVCaptureDeviceInput(device: audioDevice!)
           
           if self.session.canAddInput(videoInput) && self.session.canAddInput(audioInput){
               self.session.addInput(videoInput)
               self.session.addInput(audioInput)
           }

           if self.session.canAddOutput(self.output){
               self.session.addOutput(self.output)
           }
           
           if self.session.canAddOutput(self.photoOutput) {
               self.session.addOutput(self.photoOutput)
           }
           
           self.session.commitConfiguration()
       }
       catch {
           print(error.localizedDescription)
       }
   }
   
   func fileOutput(_ output: AVCaptureFileOutput, didFinishRecordingTo outputFileURL: URL, from connections: [AVCaptureConnection], error: Error?) {

   }
}