VNDocumentCameraViewController

Scan multipage documents with the iOS system camera

One.iOS.VNDocumentCameraViewController presents VisionKit’s document camera, including its multipage capture, crop and review UI. It requires an iOS build, a supported physical device and ios.infoPlist.NSCameraUsageDescription. isSupported is the SDK capability check, not a camera permission grant. Simulators cannot scan documents.

import { One } from 'one'

if (One.iOS.VNDocumentCameraViewController.isSupported) {
  const camera = new One.iOS.VNDocumentCameraViewController()
  camera.delegate = {
    documentCameraViewController: async (controller, result) => {
      try {
        if ('didFinishWith' in result) {
          const scan = result.didFinishWith
          for (let at = 0; at < scan.pageCount; at++) {
            const image = scan.imageOfPage(at)
            const bytes = image.pngData()
            // consume the encoded page bytes here.
          }
        } else {
          const error = result.didFailWith
          console.error(error.domain, error.code, error.localizedDescription)
        }
      } finally {
        await controller.dismiss()
      }
    },
    documentCameraViewControllerDidCancel: (controller) => {
      void controller.dismiss()
    },
  }
  await camera.present()
}

The delegate owns dismissal, as in VisionKit. Retain the controller while using it. Each controller has its own delegate and presentation state. A concurrent presentation on the same controller rejects; cancellation never fabricates a scan. Delegate errors preserve the native NSError domain, code and localized description. Presentation errors reject the promise before a delegate result.

VNDocumentCameraViewControllerDelegate.documentCameraViewController(controller, result) receives { didFinishWith: scan } or { didFailWith: error }. documentCameraViewControllerDidCancel(controller) receives cancellation. These adapt Swift’s labeled delegate overloads to JavaScript. present and dismiss adapt UIViewController presentation to the current app presenter; the native camera content is unchanged.

VNDocumentCameraScan retains the native scan. title is a string, pageCount is a number, and imageOfPage(at) returns the native page image. Indices must be integers within 0..<pageCount. The returned UIImage subset exposes size: { width, height } in points, scale, pngData() and jpegData(compressionQuality). Encoding returns an ArrayBuffer, or undefined if UIKit cannot encode the image. JPEG quality must be finite within 0...1. Pages are encoded only when requested; scan results are never replaced by synthetic images or cached file lists.

Presentation rejects with E_DOCUMENT_CAMERA_UNSUPPORTED, E_DOCUMENT_CAMERA_MANIFEST, E_DOCUMENT_CAMERA_PRESENTER, or E_DOCUMENT_CAMERA_PRESENTED. Overlapping transitions reject with E_DOCUMENT_CAMERA_TRANSITION. Invalid page indices throw E_DOCUMENT_CAMERA_PAGE; invalid encoding quality throws E_DOCUMENT_CAMERA_QUALITY.

The native fixture checks simulator unavailability and rejection with zero pages. Successful physical scanning, crop/review, cancellation and device permission failures remain required device acceptance gates.