未调用AVCaptureMetadataOutputObjectsDelegate方法

import AVFoundation

class QRCodeScanner: NSObject, AVCaptureMetadataOutputObjectsDelegate {
    private var captureSession: AVCaptureSession?
    
    func startScanning() {
        guard let captureDevice = AVCaptureDevice.default(for: .video) else {
            print("Failed to access the camera.")
            return
        }
        
        do {
            let input = try AVCaptureDeviceInput(device: captureDevice)
            
            captureSession = AVCaptureSession()
            captureSession?.addInput(input)
            
            let metadataOutput = AVCaptureMetadataOutput()
            captureSession?.addOutput(metadataOutput)
            
            metadataOutput.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
            metadataOutput.metadataObjectTypes = [.qr]
            
            let previewLayer = AVCaptureVideoPreviewLayer(session: captureSession!)
            // Add the previewLayer to your view
            
            captureSession?.startRunning()
        } catch {
            print("Failed to initialize the camera.")
        }
    }
    
    // AVCaptureMetadataOutputObjectsDelegate method
    func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {
        if let metadataObject = metadataObjects.first as? AVMetadataMachineReadableCodeObject,
           let qrCodeString = metadataObject.stringValue {
            // Handle the scanned QR code data
            print("Scanned QR code: \(qrCodeString)")
        }
    }
}