SwiftUI ScanKit

ScanKit is a simple SwiftUI package for scanning various machine-readable codes using Apple’s Vision Framework.

Getting Started

ScanKit comes in two flavors: as a View-Model pair or as an easy to plug-in SwiftUI View.

Before using either version, you should make sure your project is capable of accessing the camera.

iOS & macOS: You must include “Privacy - Camera Usage Description”, or NSCameraUsageDescription, in your info.plist.

macOS: “Camera” must be selected under “Resource Access” in “Hardened Runtime.”

ScannerView

ScannerView is a drop-in code scanner for SwiftUI that returns its results as a completion. It accepts the following parameters

• symbology: One of Apple’s VNBarcodeSymbology varieties to scan for.
• showViewfinder: A Boolean indicating whether or not to display a “viewfinder” symbol over the camera preview.
• isScanning: A Boolean binding that dictates whether or not to scan the camera feed for codes. The preview will continue to be available when false, but no further results will be sent to the completion until true.

If ScannerView is wrapped within some Navigation container, it will send two buttons to the Toolbar.

• A torch button on iOS.
• A camera picker/toggle on all platforms.

On macOS the camera picker displays all available cameras, including the continuity camera. On iOS the camera toggle switches between the front and back camera.

ScannerView‘s completion returns a stream of Result<String, ScanKitError>. A ScanKitError can be either:

• notAuthorized which indicates that camera access was not authorized.
• visionFailure which indicates that initialization failed in some way. Check the log for additional details.

Minimal Example:

@State var scanning: Bool = true

ScannerView(for: .qr, isScanning: $scanning) { result in
    switch result {
        case .success(let string):
        // To only scan once, call `self.scanning = false` here
        print(string)
        case .failure(let error):
        print(error)
    }
}

ScanKitPreview & ScanKitCamera

For a more custom experience, ScanKit exposes a unique View-Model combination of ScanKitPreview and ScanKitCamera.

ScanKitPreview is a representable wrapper around AVCapturePreviewLayer that can display the feed returned from ScanKitCamera.

ScanKitCamera interfaces directly with AVFoundation and Vision to handle available capture devices and Vision requests. It is an ObservableObject that can update the view when one of its variables change.

Results are streamed from ScanKitCamera as String via an AsyncThrowingStream. The stream finishes when ScanKitCamera().isScanning is set to false or when it encounters an error. To scan only one code at a time, simply set isScanning to false immediately upon receipt of the first result.

The resultStream can throw only two types of errors:

• notAuthorized which indicates that camera access was not authorized.
• visionFailure which indicates that initialization failed in some way. Check the log for additional details.

Various variables and functions are available from your ScanKitCamera object that allow you to interface with the device’s camera directly from SwiftUI.

Kind	Name	Purpose
var (get)	isCapturing	A Boolean indicating whether or not the camera is active.
var (get/set)	isScanning	A Boolean indicating whether or not the camera is scanning for machine readable codes.
var (get)	isTorchAvailable	A Boolean indicating whether or not the current camera has a torch available.
var (get)	isTorchOn	A Boolean indicating whether or not the torch is on. If there’s no torch, this is always false.
var (get)	isUsingBackCamera	A Boolean indicating whether or not the rear camera is active. On macOS this is always false.
var (get)	isUsingFrontCamera	A Boolean indicating whether or not the front camera is active. On macOS this is always false.
var (get)	resultsStream	An AsyncThrowingStream presenting the results of the scan operation.
var (get/set)	symbology	The current code symbology being scanned for.
var (get)	supportedSymbologies	An array of all supported symbologies.
func	cycleCaptureDevices	Cycles through available cameras. On iOS this simply toggles between the front-facing and rear-facing cameras.
func	getCamerasAsButtons	Returns a View containing all available cameras as individual Button. Each Button switches ScanKitCamera to that particular camera when pressed. This is best called within a Menu.
func	toggleTorch	Toggles the torch, if one is available.
func	start	Starts the camera. This is automatically called during appear within ScanKitPreview.
func	stop	Stops the camera. This is automatically called during disappear within ScanKitPreview.

Minimal Example:

@StateObject camera = ScanKitCamera()

var body: some View {
    ScanKitPreview(camera: camera)
        .task {
            do {
                for try await result in camera.resultsStream {
                    print(result)
                }
            } catch let error {
                print(error)
            }
        }
}

Consider looking at the implementation of ScanView for inspiration.

Considerations

It should be noted up-front that the Vision framework is not the most efficient way to handle machine readable codes. However, it is cross-platform.

If you are only targeting iOS, or are planning to target macOS via Mac Catalyst, then packages like CodeScanner that utilize AVCaptureMetadataOutput would be worth considering.

License

SwiftUI ScanKit is available under the MIT license, which permits commercial use, modification, distribution, and private use. Feel free to use it wherever and however you want!