AvCaptureSession code extraction error

Question

Im trying to extract some code out of my view controller to clean it up an d maintain as a DRY as possible code. It works fine when as follows:

class InitialRegistrationViewController: UIViewController, UINavigationControllerDelegate,  UIImagePickerControllerDelegate, NVActivityIndicatorViewable {

    var session: AVCaptureSession?
    var stillImageOutput: AVCaptureStillImageOutput?

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

        if Platform.isPhone {
            session = AVCaptureSession()
            session!.sessionPreset = AVCaptureSessionPresetPhoto

            var frontCamera = AVCaptureDevice.defaultDevice(withMediaType: AVMediaTypeVideo)
            let availableCameraDevices = AVCaptureDevice.devices(withMediaType: AVMediaTypeVideo)
            for device in availableCameraDevices as! [AVCaptureDevice] {
                if device.position == .front {
                    frontCamera = device
                }
            }

            var error: NSError?
            var input: AVCaptureDeviceInput!
            do {
                input = try AVCaptureDeviceInput(device: frontCamera)
            } catch let error1 as NSError {
                error = error1
                input = nil
                print(error!.localizedDescription)
            }

            if error == nil && session!.canAddInput(input) {
                session!.addInput(input)
                stillImageOutput = AVCaptureStillImageOutput()
                stillImageOutput?.outputSettings = [AVVideoCodecKey: AVVideoCodecJPEG]

                if session!.canAddOutput(stillImageOutput) {
                    session!.addOutput(stillImageOutput)
                    session!.startRunning()
                }
            }
        }
    }


    func capturePhoto() {
        if let videoConnection = stillImageOutput!.connection(withMediaType: AVMediaTypeVideo) {
            stillImageOutput?.captureStillImageAsynchronously(from: videoConnection, completionHandler: { (sampleBuffer, error) -> Void in
                if sampleBuffer != nil {
                    let imageData = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation(sampleBuffer)
                    let dataProvider = CGDataProvider(data: imageData as! CFData)
                    let cgImageRef = CGImage(jpegDataProviderSource: dataProvider!, decode: nil, shouldInterpolate: true, intent: CGColorRenderingIntent.defaultIntent)
                    let image = UIImage(cgImage: cgImageRef!, scale: 1.0, orientation: UIImageOrientation.right)
                    self.profileImage.image = image
                }
            })
        }
    }
}

but when i extract to a helper like below:

import UIKit import AVFoundation

class ProfilePhoto {

    var session: AVCaptureSession?
    var stillImageOutput: AVCaptureStillImageOutput?

    func startSession() {

        if Platform.isPhone {
            session = AVCaptureSession()
            session!.sessionPreset = AVCaptureSessionPresetPhoto

            var frontCamera = AVCaptureDevice.defaultDevice(withMediaType: AVMediaTypeVideo)
            let availableCameraDevices = AVCaptureDevice.devices(withMediaType: AVMediaTypeVideo)
            for device in availableCameraDevices as! [AVCaptureDevice] {
                if device.position == .front {
                    frontCamera = device
                }
            }

            var error: NSError?
            var input: AVCaptureDeviceInput!
            do {
                input = try AVCaptureDeviceInput(device: frontCamera)
            } catch let error1 as NSError {
                error = error1
                input = nil
                print(error!.localizedDescription)
            }

            if error == nil && session!.canAddInput(input) {
                session!.addInput(input)
                stillImageOutput = AVCaptureStillImageOutput()
                stillImageOutput?.outputSettings = [AVVideoCodecKey: AVVideoCodecJPEG]

                if session!.canAddOutput(stillImageOutput) {
                    session!.addOutput(stillImageOutput)
                    session!.startRunning()
                }
            }
        }
    }

    func capture() -> UIImage {
        var image: UIImage!

        if let videoConnection = stillImageOutput!.connection(withMediaType: AVMediaTypeVideo) {
            stillImageOutput?.captureStillImageAsynchronously(from: videoConnection, completionHandler: { (sampleBuffer, error) -> Void in
                if sampleBuffer != nil {
                    let cgImageRef = self.setBufferData(sampleBuffer: sampleBuffer!)
                    image = UIImage(cgImage: cgImageRef, scale: 1.0, orientation: UIImageOrientation.right)
                }
            })
        }
        return image
    }

    func setBufferData(sampleBuffer: CMSampleBuffer ) -> CGImage {
        let imageData = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation(sampleBuffer)
        let dataProvider = CGDataProvider(data: imageData as! CFData)
        let cgImageRef = CGImage(jpegDataProviderSource: dataProvider!, decode: nil, shouldInterpolate: true, intent: CGColorRenderingIntent.defaultIntent)
        return cgImageRef!
    }
}

where in InitialRegistrationViewController i call:

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    profilePhoto.startSession()
}


func capturePhoto() {
    profileImage.image = profilePhoto.capture()
}

I get fatal error: unexpectedly found nil while unwrapping an Optional value when returning the image in profilePhoto.capture().

I dont understand how the session works as im new to ios but i think its because the session is ending(?) when i try to capture the image? Any insight would be great. Thanks

UPDATE: I upvotes the answer given as its close enough, below is what worked for me.

    func capture(completion: @escaping (UIImage?) -> Void) {

    if let videoConnection = stillImageOutput!.connection(withMediaType: AVMediaTypeVideo) {
        stillImageOutput?.captureStillImageAsynchronously(from: videoConnection, completionHandler: { (sampleBuffer, error) -> Void in
            if sampleBuffer != nil {
                let cgImageRef = self.setBufferData(sampleBuffer: sampleBuffer!)
                let image: UIImage! = UIImage(cgImage: cgImageRef, scale: 1.0, orientation: UIImageOrientation.right)
                completion(image)
            } else {
                completion(nil)
            }
        })
    } else {
        completion(nil)
    }
}

Answer 1

Your capture() method makes an asynchronous call to get the UIImage, therefore when it returns [immediately] the value returned is always nil.

The article @dan suggested shows a callback pattern that can be used to return the image to the caller, make sure you understand this mechanism before proceeding.

    func capture(result: (image: UIImage?) -> Void) -> UIImage 
    {
        if let videoConnection = stillImageOutput!.connection(withMediaType: AVMediaTypeVideo) 
        {
            stillImageOutput?.captureStillImageAsynchronously(from: videoConnection, completionHandler:
            { (sampleBuffer, error) -> Void in

             if sampleBuffer != nil 
             {
                let cgImageRef = self.setBufferData(sampleBuffer: sampleBuffer!)
                var image: UIImage! = UIImage(cgImage: cgImageRef, scale: 1.0, orientation: UIImageOrientation.right)
                result(image: image)
             }
             else
                result(image: nil)   

            })
        }
        else
            result(image: nil)
    }

And to call it, you could use

capture(){(image: UIImage?) -> Void in
    //use the image that was just retrieved
}

You've now made your capture() method asynchronous, and report its return value via a callback.