I can't seem to make a custom camera. "Constant used before initialized"

Question

I am using swift 3. I'm trying to make a custom camera. But no matter how many tutorials I follow, or many of apple documentations, There's always an error.

class ViewController: UIViewController, UIImagePickerControllerDelegate {

@IBOutlet var cameraView: UIView!

var captureSession : AVCaptureSession?
var stillImageOutput : AVCaptureStillImageOutput?
var previewLayer : AVCaptureVideoPreviewLayer?

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    captureSession = AVCaptureSession()
    captureSession?.sessionPreset = AVCaptureSessionPreset1920x1080

    let backCamera = AVCaptureDevice.defaultDevice(withMediaType: AVMediaTypeVideo)
    let error : NSError?

    do {

        let input = try! AVCaptureDeviceInput (device: backCamera)
        if (error == nil && captureSession?.canAddInput(input) != nil) {

            captureSession?.addInput(input)

            stillImageOutput = AVCaptureStillImageOutput()
            stillImageOutput?.outputSettings = [AVVideoCodecKey: AVVideoCodecJPEG]

            if (captureSession?.canAddOutput(stillImageOutput) != nil) {
                captureSession?.addOutput(stillImageOutput)

                previewLayer = AVCaptureVideoPreviewLayer (session: captureSession)
                previewLayer?.videoGravity = AVLayerVideoGravityResizeAspect
                previewLayer?.connection.videoOrientation = AVCaptureVideoOrientation.portrait
                cameraView.layer.addSublayer(previewLayer!)
                captureSession?.startRunning()
            }
        }
    } catch {

    }
}


override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    previewLayer?.frame = cameraView.bounds
}

on this line, if (error == nil && captureSession?.canAddInput(input) != nil) { , there is an error saying that the constant "error" has been used before initialized. I don't really understand this. Thank you in advance.

Answer 1

As the error message states, you are using error before initializing it. You can fix this by initializing it with nil:

let error: NSError? = nil

or even better:

let error: Error? = nil

Actually, you do not ever use error, so you can simply remove it:

...
//let error : NSError? delete this line

do {
    ...
    if (/* error == nil && delete this */captureSession?.canAddInput(input) != nil) {