使用AVCaptureSession读取QR码

Question

我们已经使用AVCaptureSession在收据上实现了QRCode读取。我们注意到的一个问题是，它在读取QRCode的命中率上相当挑剔。你真的必须努力让它认识到收据上有QRCode。我试着看看是否有人发表了关于如何提高命中率的材料。我已经实现了AutoFocus，这有点帮助。

我确实看过：Reading on QRCodes on iOS with AVCaptureSession -- alignment issues?但是那里没有可行的建议。

有关其他方法的任何想法吗？

以下是读者代码：

import UIKit
import AVFoundation

final class BarcodeReader: NSObject {

    fileprivate var captureSession: AVCaptureSession?
    fileprivate var videoPreviewLayer: AVCaptureVideoPreviewLayer?

    fileprivate unowned let barcodeReaderDelegate: BarcodeReaderDelegate

    init(barcodeReaderDelegate: BarcodeReaderDelegate) {
        self.barcodeReaderDelegate = barcodeReaderDelegate
    }

    func start(in view: UIView) throws {
        if captureSession == nil {
            captureSession = try configuredCaptureSession()
        }

        if videoPreviewLayer == nil {
            videoPreviewLayer = AVCaptureVideoPreviewLayer(session: captureSession!)
            videoPreviewLayer!.videoGravity = AVLayerVideoGravityResizeAspectFill
            videoPreviewLayer!.frame = view.layer.bounds
            view.layer.addSublayer(videoPreviewLayer!)
        }

        captureSession!.startRunning()
    }

    fileprivate func configuredCaptureSession() throws -> AVCaptureSession {
        let captureSession = AVCaptureSession()

        // NOTE: Remember to add a message in your Info.plist file under the
        //       key NSCameraUsageDescription or this will crash the app.
        let device = AVCaptureDevice.defaultDevice(withMediaType: AVMediaTypeVideo)

        // make sure that auto focus is turned on
        if (device?.isFocusModeSupported(.continuousAutoFocus))! {
            try device?.lockForConfiguration()
            device?.focusMode = .continuousAutoFocus
            device?.unlockForConfiguration()
        }

        let input = try AVCaptureDeviceInput(device: device)
        captureSession.addInput(input)

        let output = AVCaptureMetadataOutput()
        captureSession.addOutput(output)
        output.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
        output.metadataObjectTypes = [AVMetadataObjectTypeQRCode]

        return captureSession
    }

    func stop() {
        captureSession?.stopRunning()
    }
}

extension BarcodeReader: AVCaptureMetadataOutputObjectsDelegate {

    func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [Any]!, from connection: AVCaptureConnection!) {
        guard let metadataObject = metadataObjects.first as? AVMetadataMachineReadableCodeObject else { return }
        guard metadataObject.type == AVMetadataObjectTypeQRCode else { return 
}
        stop()
        barcodeReaderDelegate.barcodeReader(self, found: metadataObject.stringValue)
    }

}

protocol BarcodeReaderDelegate: class {
    func barcodeReader(_ barcodeReader: BarcodeReader, found code: String)
}