Why is previewLayer returning nil when I try to get bounds?

Question

This view controller is being called from a button on another storyboard. Every time I tap the button I get

fatal error: unexpectedly found nil while unwrapping an Optional value 2017-04-16 21:00:39.929042 FaceOnACase[757:377279] fatal error: unexpectedly found nil while unwrapping an Optional value

on the line self.previewLayer?.frame = self.previewView.bounds.

I had this code working earlier in a separate, single view app I was working on, but when I transferred the code over and hooked up the IBOutlets, I can't get it working for some reason.

I couldn't find a similar issue, and I'm unsure how to correct this. Any help is appreciated, thanks.

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 is not returning nil. It's previewView that is nil. Make sure you have hooked this up correctly as an outlet in the storyboard.

Also what you're doing is too early. You cannot start a capture session in viewDidLoad. Remember, this means the view exists, but it is not even in the interface yet! You at least need an interface in order to start the capture session.