ios - 相机预览层未显示

我正在用swift创建一个带有自定义相机视图的应用程序，但视图只是黑色的
似乎实时预览窗口没有出现，这在我的Xcode应用程序、iPad上的swift playgrounds和mac上的swift playgrounds中都不起作用。
代码如下：

import UIKit
import CoreImage
import CoreFoundation
import AVKit
import AVFoundation

let view = UIView()
var str = "Hello, playground"
import PlaygroundSupport
var captureSession: AVCaptureSession?
var stillImageOutput: AVCapturePhotoOutput?
var previewLayer: AVCaptureVideoPreviewLayer?







captureSession = AVCaptureSession()
captureSession!.sessionPreset = AVCaptureSessionPresetPhoto
var backCamera = AVCaptureDevice.defaultDevice(withMediaType:     AVMediaTypeVideo)
 var error: NSError?
 //var lol = AVCaptureInput();
 // var input = AVCaptureDeviceInput(device: backCamera, error: &error)

 var input = try AVCaptureDeviceInput(device: backCamera)

//error

if error == nil && captureSession!.canAddInput(input) {
    captureSession!.addInput(input)
    stillImageOutput = AVCapturePhotoOutput()
//    stillImageOutput?.outputSettings = [AVVideoCodecKey: AVVideoCodecJPEG]
    captureSession!.addOutput(stillImageOutput)

}

 previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
 view.layer.addSublayer(previewLayer!)
 previewLayer!.frame = view.bounds
 PlaygroundPage.current.liveView = view
 //PlaygroundPage.currentPage.liveView = view

最佳答案

我可以从你的代码中看到一个问题，那就是你永远不会启动捕获会话。使用captureSession.startRunning()