get a SubLayer with swift2 and Xcode 7 - ios

Question

I would save a sublayer. But I can not get a target.
I want to save the layer that is displayed on the screen that contains the view of the camera. When I want it back, I get a white image. I concluded that I targeted my male layer when I record in dernnière function.
Here is my code:
#IBOutlet weak var blutEffect: UIVisualEffectView!
#IBOutlet weak var background: UIView! // vu d'affichage
var previewLayer = AVCaptureVideoPreviewLayer()
var captureSession = AVCaptureSession()
override func viewDidLoad() {
super.viewDidLoad()
camera()
}
#IBAction func takePhoto(sender: AnyObject) {
captureSession.stopRunning()
}
func camera () {
captureSession = AVCaptureSession()
previewLayer = AVCaptureVideoPreviewLayer()
var captureDevice : AVCaptureDevice?
let devices = AVCaptureDevice.devices()
captureSession.sessionPreset = AVCaptureSessionPresetHigh
background.layer.sublayers?.removeAll()
for device in devices {
if (device.hasMediaType(AVMediaTypeVideo)) {
if(device.position == AVCaptureDevicePosition.Back) {
captureDevice = device as? AVCaptureDevice
if captureDevice != nil {
do {
try captureSession.addInput(AVCaptureDeviceInput(device: captureDevice))
} catch _ as NSError {
print("ERROR")
}
previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
self.background.layer.addSublayer(previewLayer)
previewLayer.frame = self.background.layer.frame
captureSession.startRunning()
}
}
}
}
}
func screenShotMethod() {
UIGraphicsBeginImageContext(background.layer.frame.size)
background.layer.renderInContext(UIGraphicsGetCurrentContext())
let image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
//Save it to the camera roll
UIImageWriteToSavedPhotosAlbum(image, nil, nil, nil)
}
Thanks for your help !