DocumentsScannerViewController.swift

// presenting VNDocumentCameraViewController
let scanVC = VNDocumentCameraViewController()
scanVC.delegate = self
present(scanVC, animated: true)

// VNDocumentCameraViewControllerDelegate conformance
extension DocumentsScannerViewController: VNDocumentCameraViewControllerDelegate {

    func documentCameraViewController(_ controller: VNDocumentCameraViewController, didFinishWith scan: VNDocumentCameraScan) {

        var documentImages: [UIImage] = []
        for page in 0...scan.pageCount-1 {
            let image = scan.imageOfPage(at: page)
            documentImages.append(image)
        }

        controller.dismiss(animated: true, completion: nil)
        finishedScanningDocuments(images: documentImages)
    }

    func documentCameraViewController(_ controller: VNDocumentCameraViewController, didFailWithError error: Error) {
        showError(message: "Something unexpected happened, please try again later")
        controller.dismiss(animated: true)
    }

    func documentCameraViewControllerDidCancel(_ controller: VNDocumentCameraViewController) {
        controller.dismiss(animated: true)
    }

}