转至控制器需要 5-10 秒才能显示

Question

我正在使用 swift 4 并且有一个应用程序，人们可以通过我的应用程序打开他们的 phone 相机。我有一个名为 CameraController 的 ViewController，它具有默认值 UIView，我在名为 CameraView 的顶部有一个视图，它显示用户相机和其他按钮.

当我单击其中一个按钮时，它会通过 segue (PlacesController) 将我带到另一个视图控制器。当我关闭 PlacesController 我回到 CameraController 但是子视图现在需要大约 8 或 10 秒才能再次显示。

有什么方法可以在保持当前子视图的同时转到另一个 Controller？

同样的问题是，当我转到我的 segue 控制器 PlaceController 然后返回我的 CameraController 时，大约需要 8 或 10 秒才能看到相机和子图层。特别是下面这段代码，我想知道我是否可以让我的子层保持静止运行因为等待 10 秒让它显示太多了。

self.CameraView.layer.insertSublayer(previewLayer!, at: 0)

这是我的代码：

class CameraController: UIViewController {
    @IBOutlet weak var CameraView: UIView!
     var previewLayer: AVCaptureVideoPreviewLayer?
     let captureSession = AVCaptureSession()


  override func viewDidLoad() {
        super.viewDidLoad()


    }
 override func viewDidAppear(_ animated: Bool) {
           DispatchQueue.main.async {
             self.beginSession()
        }

    func beginSession() {
   // gets the camera showing and displays buttons on top of it
        previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
        self.CameraView.layer.insertSublayer(previewLayer!, at: 0)
        previewLayer?.frame = self.CameraView.layer.bounds

        previewLayer?.videoGravity = AVLayerVideoGravity.resizeAspectFill
        captureSession.startRunning()
        stillImageOutput.outputSettings = [AVVideoCodecKey: AVVideoCodecType.jpeg]
        if captureSession.canAddOutput(stillImageOutput) {
            captureSession.addOutput(stillImageOutput)
        }
    }


  override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "PlacesController" {
            let PlaceAreaSearchC: ColorC = segue.destination as! PlacesController
            PlaceAreaSearchC.delegate = self
        }
    }

 // PlacesController
class PlacesController: UIViewController {
    @IBAction func backAction(_ sender: Any) {
   // This is how I go back to my view CameraController
         dismiss(animated: true, completion: nil)
    }
 }

Answer 1

AVCaptureSession startRunning 调用正在阻塞您的主线程，因此延迟。

正如 startRunning()’s Apple Doc 中所说：

The startRunning() method is a blocking call which can take some time, therefore you should perform session setup on a serial queue so that the main queue isn't blocked (which keeps the UI responsive).

Answer 2

除了的 Lyndsey Scott:

    let backCamera: AVCaptureDevice? = AVCaptureDevice.default(AVCaptureDevice.DeviceType.builtInWideAngleCamera, for: AVMediaType.video, position: AVCaptureDevice.Position.back)

    guard let camera = backCamera, let deviceInput = try? AVCaptureDeviceInput(device: camera) else {
        self?.didReceive(captureSession: nil)
        return
    }

    DispatchQueue.global(qos: .userInitiated).async { [weak self] in
        let deviceOutput = AVCapturePhotoOutput()
        let cameraSession = AVCaptureSession()

        cameraSession.beginConfiguration()
        cameraSession.sessionPreset = .low
        if cameraSession.canAddInput(deviceInput) {
            cameraSession.addInput(deviceInput)
        }
        if cameraSession.canAddOutput(deviceOutput) {
            cameraSession.addOutput(deviceOutput)
        }
        cameraSession.commitConfiguration()
        cameraSession.startRunning()
        DispatchQueue.main.async {
            self?.didReceive(captureSession: cameraSession)
        }
    }

Xcode 10.0, Swift 4.2

转至控制器需要 5-10 秒才能显示

Segue to controller takes 5-10 seconds to display

camera

ios

avcapturesession

segue

swift