AVCaptureDeviceInput Unexpectedly found nil while unwrapping an Optional value - swift

Question

I'm trying to get the image of the capturing device but it keeps returning nil by if let input... and I can't find a solution.
It tries to catch the error but it instantly cashes..
let backCamera = AVCaptureDevice.default(for: AVMediaType.video)
do {
if let input = try AVCaptureDeviceInput(device: backCamera!) as? AVCaptureInput {
if (captureSession?.canAddInput(input))! {
captureSession?.addInput(input)
stillImageOutput = AVCapturePhotoOutput()
let settings = AVCapturePhotoSettings()
let settingsFormat = [AVVideoCodecKey : AVVideoCodecType.jpeg]
settings.previewPhotoFormat = settingsFormat
stillImageOutput?.capturePhoto(with: settings, delegate: self as! AVCapturePhotoCaptureDelegate)
if (captureSession?.canAddOutput(stillImageOutput!))! {
captureSession?.addOutput(stillImageOutput!)
previewLayer = AVCaptureVideoPreviewLayer(session: captureSession!)
previewLayer?.videoGravity = AVLayerVideoGravity.resizeAspect
previewLayer?.connection?.videoOrientation = AVCaptureVideoOrientation.portrait
cameraView.layer.addSublayer(previewLayer!)
captureSession?.startRunning()
}
}
}
} catch let error as NSError {
print("Error: \(error)")
}

Answer 1

It's not your error throwing that's causing the crash - it's all your force unwrapping. backCamera, captureSession, stillImageOutput, and previewLayer are all Optionals, but you're force unwrapping all of them every time. Why not use guard statements or optional binding to avoid those crashes? Ultimately you can't run any of that code if those items are nil, so I'd refactor your code like this:
//Use guard to make sure you have a non-nil captureSession and a default device for .video
guard let captureSession = captureSession, let backCamera = AVCaptureDevice.default(for: AVMediaType.video) else { return }
do {
if let input = try AVCaptureDeviceInput(device: backCamera) as? AVCaptureInput {
if (captureSession.canAddInput(input)) {
captureSession.addInput(input)
stillImageOutput = AVCapturePhotoOutput()
//Since stillImageOutput is an Optional I'm putting in another guard just to avoid having to deal with it as an Optional
guard let stillImageOutput = stillImageOutput else { return }
let settings = AVCapturePhotoSettings()
let settingsFormat = [AVVideoCodecKey : AVVideoCodecType.jpeg]
settings.previewPhotoFormat = settingsFormat
stillImageOutput.capturePhoto(with: settings, delegate: self as! AVCapturePhotoCaptureDelegate)
if (captureSession.canAddOutput(stillImageOutput)) {
captureSession.addOutput(stillImageOutput)
previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
//Same as above - since you declared previewLayer as Optional I'll guard so I don't have to deal with it as an Optional
guard let previewLayer = previewLayer else { return }
previewLayer.videoGravity = AVLayerVideoGravity.resizeAspect
previewLayer.connection?.videoOrientation = AVCaptureVideoOrientation.portrait
cameraView.layer.addSublayer(previewLayer)
captureSession.startRunning()
}
}
}
} catch let error {
print("Error: \(error)")
}
Honestly some of this is a bit overkill, so it's down to a bit of personal preference, but with something like AVCaptureDevice.default... where it truly may or may not be nil depending on the actual device you probably don't want to let it crash if it doesn't exist.