ios – 如何使用Swift在AVCaptureVideoPreviewLayer的特定区域捕获QR码数据？

我正在创建一个iPad应用程序,其中一个功能是扫描QR码.我有QR扫描部分工作,但我的问题是iPad屏幕非常大,我将扫描一张纸的小QR码,同时可以看到许多QR码.我想指定显示器的较小区域是唯一可以实际捕获QR码的区域,因此用户更容易扫描他们想要的特定QR码.

我目前已经制作了一个带有红色边框的临时UIView,它以页面为中心,作为我希望用户扫描QR码的示例.它看起来像这样：

我已经到处寻找一个答案,我可以如何定位AVCaptureVideoPreviewLayer的特定区域来收集QR码数据,我发现建议使用“rectOfInterest”和AVCaptureMetadataOutput.我试图这样做,但是当我将rectOfInterest设置为与我用于正确显示的UIView相同的坐标和大小时,我无法扫描/识别任何QR码.有人可以告诉我为什么可扫描区域与看到的UIView的位置不匹配,如何让rectOfInterest在我添加到屏幕的红色边框内？

这是我目前使用的扫描功能的代码：

func startScan() {
    // Get an instance of the AVCaptureDevice class to initialize a device object and provide the video
    // as the media type parameter.
    let captureDevice = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)

    // Get an instance of the AVCaptureDeviceInput class using the prevIoUs device object.
    var error:NSError?
    let input: AnyObject! = AVCaptureDeviceInput.deviceInputWithDevice(captureDevice,error: &error)

    if (error != nil) {
        // If any error occurs,simply log the description of it and don't continue any more.
        println("\(error?.localizedDescription)")
        return
    }

    // Initialize the captureSession object.
    captureSession = AVCaptureSession()
    // Set the input device on the capture session.
    captureSession?.addInput(input as! AVCaptureInput)

    // Initialize a AVCaptureMetadataOutput object and set it as the output device to the capture session.
    let captureMetadataOutput = AVCaptureMetadataOutput()
    captureSession?.addOutput(captureMetadataOutput)

    // calculate a centered square rectangle with red border
    let size = 300
    let screenWidth = self.view.frame.size.width
    let xPos = (CGFloat(screenWidth) / CGFloat(2)) - (CGFloat(size) / CGFloat(2))
    let scanRect = CGRect(x: Int(xPos),y: 150,width: size,height: size)

    // create UIView that will server as a red square to indicate where to place QRCode for scanning
    scanAreaView = UIView()
    scanAreaView?.layer.borderColor = UIColor.redColor().CGColor
    scanAreaView?.layer.borderWidth = 4
    scanAreaView?.frame = scanRect

    // Set delegate and use the default dispatch queue to execute the call back
    captureMetadataOutput.setMetadataObjectsDelegate(self,queue: dispatch_get_main_queue())
    captureMetadataOutput.MetadataObjectTypes = [AVMetadataObjectTypeQRCode]
    captureMetadataOutput.rectOfInterest = scanRect


    // Initialize the video preview layer and add it as a sublayer to the viewPreview view's layer.
    videoPreviewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
    videoPreviewLayer?.videoGravity = AVLayerVideoGravityResizeAspectFill
    videoPreviewLayer?.frame = view.layer.bounds
    view.layer.addSublayer(videoPreviewLayer)

    // Start video capture.
    captureSession?.startRunning()

    // Initialize QR Code Frame to highlight the QR code
    qrCodeFrameView = UIView()
    qrCodeFrameView?.layer.borderColor = UIColor.greenColor().CGColor
    qrCodeFrameView?.layer.borderWidth = 2
    view.addSubview(qrCodeFrameView!)
    view.bringSubviewToFront(qrCodeFrameView!)

    // Add a button that will be used to close out of the scan view
    videoBtn.setTitle("Close",forState: .normal)
    videoBtn.setTitleColor(UIColor.blackColor(),forState: .normal)
    videoBtn.backgroundColor = UIColor.grayColor()
    videoBtn.layer.cornerRadius = 5.0;
    videoBtn.frame = CGRectMake(10,30,70,45)
    videoBtn.addTarget(self,action: "pressClose:",forControlEvents: .TouchUpInside)
    view.addSubview(videoBtn)

    view.addSubview(scanAreaView!)

}

更新
我不认为这是重复的原因是因为引用的其他帖子在Objective-C中,而我的代码在Swift中.对于我们这些刚接触iOS的人来说,翻译这两者并不容易.此外,引用的帖子的答案并未显示解决其问题的代码中的实际更新.他留下了关于必须使用MetadataOutputRectOfInterestForRect方法来转换矩形坐标的一个很好的解释,但我似乎仍然无法使这个方法起作用,因为我不清楚如何在没有示例的情况下这应该如何工作.

func convertRectOfInterest(rect: CGRect) -> CGRect {
    let screenRect = self.view.frame
    let screenWidth = screenRect.width
    let screenHeight = screenRect.height
    let newX = 1 / (screenWidth / rect.minX)
    let newY = 1 / (screenHeight / rect.minY)
    let newWidth = 1 / (screenWidth / rect.width)
    let newHeight = 1 / (screenHeight / rect.height)
    return CGRect(x: newX,y: newY,width: newWidth,height: newHeight)
}