iOS 13 - Camera hangs in VNDocumentCameraViewController - swift

Question

When using VisionKit's VNDocumentCameraViewController for scanning documents the camera hangs after some seconds. The scan is implemented in a ViewController, which is used in SwiftUI.
The implementation of a DocumentScannerViewController:
import UIKit
import VisionKit
import SwiftUI
final class DocumentScannerViewController: UIViewController, VNDocumentCameraViewControllerDelegate, UIViewControllerRepresentable {
public typealias UIViewControllerType = DocumentScannerViewController
public func makeUIViewController(context: UIViewControllerRepresentableContext<DocumentScannerViewController>) -> DocumentScannerViewController {
return DocumentScannerViewController()
}
public func updateUIViewController(_ uiViewController: DocumentScannerViewController, context: UIViewControllerRepresentableContext<DocumentScannerViewController>) {
}
override func viewDidLoad() {
super.viewDidLoad()
let scannerViewController = VNDocumentCameraViewController()
scannerViewController.delegate = self as VNDocumentCameraViewControllerDelegate
view.addSubview(scannerViewController.view)
}
func documentCameraViewController(_ controller: VNDocumentCameraViewController, didFinishWith scan: VNDocumentCameraScan) {
}
func documentCameraViewControllerDidCancel(_ controller: VNDocumentCameraViewController) {
}
func documentCameraViewController(_ controller: VNDocumentCameraViewController, didFailWithError error: Error) {
}
}
And the implementation of the ContentView:
import SwiftUI
struct ContentView: View {
var body: some View {
DocumentScannerViewController()
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
The document scan camera launches and works for a short period of time. Then camera just stops moving.
Any idea what causes this behavior?

Answer 1

Apple does provide a way to use ViewControllers inside SwiftUI view with UIViewControllerRepresentable which you have to implement this way.
First declare your View as follows:
import SwiftUI
import UIKit
import Vision
import VisionKit
struct ScanningVNDocumentView: UIViewControllerRepresentable {
// implement your custom init() in case ..
typealias UIViewControllerType = VNDocumentCameraViewController
func makeUIViewController(context: UIViewControllerRepresentableContext<ScanningVNDocumentView>) -> VNDocumentCameraViewController {
let viewController = VNDocumentCameraViewController()
viewController.delegate = context.coordinator
return viewController
}
func updateUIViewController(_ uiViewController: VNDocumentCameraViewController, context: UIViewControllerRepresentableContext<ScanningVNDocumentView>) {
}
func makeCoordinator() -> Coordinator {
//Coordinator is Apple bridge between SwiftUI and ViewController
return Coordinator() `// this basically call init of the UIViewControllerRepresentable above`
}
final class Coordinator: NSObject, VNDocumentCameraViewControllerDelegate {
#Environment(\.presentationMode) var presentationMode
init() {
}
// implement VNDocumentCameraViewControllerDelegate methods where you can dismiss the ViewController
func documentCameraViewController(_ controller: VNDocumentCameraViewController, didFinishWith scan: VNDocumentCameraScan) {
print("user did press save with scanned docs numbers \(scan.pageCount) ")
}
func documentCameraViewControllerDidCancel(_ controller: VNDocumentCameraViewController) {
print("Did press cancel")
}
func documentCameraViewController(_ controller: VNDocumentCameraViewController, didFailWithError error: Error) {
print("Document camera view controller did finish with error ", error)
}
}
}
You can now call your view this way:
var body: some View {
ScanningVNDocumentView()
}