当我试图获得边界时，为什么previewLayer返回nil？

Question

从另一个故事板上的按钮调用此视图控制器。每次点击按钮我都会

  

致命错误：在展开Optional值时意外发现nil   2017-04-16 21：00：39.929042 FaceOnACase [757：377279]致命错误：在展开可选值时意外发现nil

就行self.previewLayer？.frame = self.previewView.bounds。

我之前在我正在处理的单独的单一视图应用程序中使用了此代码，但是当我将代码转移并连接到IBOutlets时，由于某种原因我无法使其工作。

我找不到类似的问题，我不确定如何纠正这个问题。感谢任何帮助。谢谢。

import UIKit
import AVFoundation

class CaptureController: UIViewController, AVCapturePhotoCaptureDelegate {
    var captureSesssion: AVCaptureSession!
    var cameraOutput: AVCapturePhotoOutput!
    var previewLayer: AVCaptureVideoPreviewLayer!
    @IBOutlet weak var capturedImage: UIImageView!
    @IBOutlet weak var previewView: UIView!
    override func viewDidLoad() {
        super.viewDidLoad()
        captureSesssion = AVCaptureSession()
        captureSesssion.sessionPreset = AVCaptureSessionPresetPhoto
        cameraOutput = AVCapturePhotoOutput()
        let device = AVCaptureDevice.defaultDevice(withMediaType: AVMediaTypeVideo)
        do {
            let input = try AVCaptureDeviceInput(device: device)
            if (captureSesssion.canAddInput(input)) {
                captureSesssion.addInput(input)
                if (captureSesssion.canAddOutput(cameraOutput)) {
                    captureSesssion.addOutput(cameraOutput)
                    previewLayer = AVCaptureVideoPreviewLayer(session: captureSesssion)
                    self.previewLayer?.frame = self.previewView.bounds
                    previewView.layer.addSublayer(previewLayer)
                    captureSesssion.startRunning()
                }
            } else {
                print("issue here : captureSesssion.canAddInput")
            }
        } catch let error {
            print("error \(error.localizedDescription)")
        }
    }
    // Take picture button
    @IBAction func didPressTakePhoto(_ sender: UIButton) {
        let settings = AVCapturePhotoSettings()
        let previewPixelType = settings.availablePreviewPhotoPixelFormatTypes.first!
        let previewFormat = [
            kCVPixelBufferPixelFormatTypeKey as String: previewPixelType,
            kCVPixelBufferWidthKey as String: 160,
            kCVPixelBufferHeightKey as String: 160
        ]
        settings.previewPhotoFormat = previewFormat
        cameraOutput.capturePhoto(with: settings, delegate: self)
    }
    // callBack from take picture
    func capture(_ captureOutput: AVCapturePhotoOutput,  didFinishProcessingPhotoSampleBuffer photoSampleBuffer: CMSampleBuffer?,  previewPhotoSampleBuffer: CMSampleBuffer?, resolvedSettings:  AVCaptureResolvedPhotoSettings, bracketSettings:   AVCaptureBracketedStillImageSettings?, error: Error?) {
        if let error = error {
            print("error occured : \(error.localizedDescription)")
        }
        if  let sampleBuffer = photoSampleBuffer,
            let previewBuffer = previewPhotoSampleBuffer,
            let dataImage =  AVCapturePhotoOutput.jpegPhotoDataRepresentation(forJPEGSampleBuffer:  sampleBuffer, previewPhotoSampleBuffer: previewBuffer) {
            print(UIImage(data: dataImage)?.size as Any)
            let dataProvider = CGDataProvider(data: dataImage as CFData)
            let cgImageRef: CGImage! = CGImage(jpegDataProviderSource: dataProvider!, decode: nil, shouldInterpolate: true, intent: .defaultIntent)
            let image = UIImage(cgImage: cgImageRef, scale: 1.0, orientation: UIImageOrientation.right)
            self.capturedImage.image = image
        } else {
            print("some error here")
        }
    }
    // This method you can use somewhere you need to know camera permission   state
    func askPermission() {
        print("here")
        let cameraPermissionStatus =  AVCaptureDevice.authorizationStatus(forMediaType: AVMediaTypeVideo)
        switch cameraPermissionStatus {
        case .authorized:
            print("Already Authorized")
        case .denied:
            print("denied")
            let alert = UIAlertController(title: "Sorry :(" , message: "But  could you please grant permission for camera within device settings",  preferredStyle: .alert)
            let action = UIAlertAction(title: "Ok", style: .cancel,  handler: nil)
            alert.addAction(action)
            present(alert, animated: true, completion: nil)
        case .restricted:
            print("restricted")
        default:
            AVCaptureDevice.requestAccess(forMediaType: AVMediaTypeVideo, completionHandler: {
                [weak self]
                (granted :Bool) -> Void in
                if granted == true {
                    // User granted
                    print("User granted")
                    DispatchQueue.main.async(){
                        //Do smth that you need in main thread
                    }
                }
                else {
                    // User Rejected
                    print("User Rejected")
                    DispatchQueue.main.async(){
                        let alert = UIAlertController(title: "WHY?" , message:  "Camera it is the main feature of our application", preferredStyle: .alert)
                        let action = UIAlertAction(title: "Ok", style: .cancel, handler: nil)
                        alert.addAction(action)
                        self?.present(alert, animated: true, completion: nil)
                    }
                }
            })
        }
    }
}

Answer 1

previewLayer 不返回nil。它是previewView，nil。确保您已正确地将其作为故事板中的插座连接起来。

你所做的还为时尚早。您无法在viewDidLoad中启动捕获会话。请记住，这意味着视图存在，但它甚至还不在界面中！您至少需要一个界面才能启动捕获会话。