Question

我的应用程序中有一个扫描ISBN代码的视图控制器，这是类：

isbn

}

它扫描确切的代码并将其保存在var isbn中。错误是当我执行segue时，因为它多次返回到前一个视图控制器而我只想要一个。我试图打印变量CREATE SEQUENCE SEQ_USR MINVALUE 1 MAXVALUE 1000 START WITH 1 INCREMENT BY 1;并多次打印，如下所示：“ 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666 9788804648666"

Answer 1

您的问题来自于检测到QR码时仍在运行的 captureSession ，因此多次调用 performSegue 。相反，你应该替换

if metadataObj.stringValue != nil {
  messageLabel.text = metadataObj.stringValue
  QRScannerController.isbn = metadataObj.stringValue
  print(QRScannerController.isbn)
  self.performSegue(withIdentifier: "showISBN", sender: self)
}

通过

if let code = metadataObj.stringValue {
  saveAndDismiss(code: code)
}

并添加

fileprivate func saveAndDismiss(code code: String) {
  messageLabel.text = code
  QRScannerController.isbn = code
  print(QRScannerController.isbn)
  performSegue(withIdentifier: "showISBN", sender: self)
  captureSession?.stopRunning()
}

此外，你的isbn var不应该是静态的。它应该是私有的，您可以在méthode prepareForSegue

中将值赋给segue目标控制器

Answer 2

我甚至会替换整个功能：

func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [Any]!, from connection: AVCaptureConnection!) {
  guard let data = metadataObjects,
  data.count > 0 else {
    qrCodeFrameView?.frame = CGRect.zero
    messageLabel.text = "No QR/barcode is detected"
    return
  }

  // Get the metadata object.
  if let metadataObj = metadataObjects[0] as? AVMetadataMachineReadableCodeObject,
  supportedCodeTypes.contains(metadataObj.type) {
    // If the found metadata is equal to the QR code metadata then update the status label's text and set the bounds
    if let barCodeObject = videoPreviewLayer?.transformedMetadataObject(for: metadataObj) {
     qrCodeFrameView?.frame = barCodeObject.bounds
    }

    if let code = metadataObj.stringValue {
      saveAndDismiss(code: code)
    }
  }
}

扫描ISBN代码后出错

2 个答案: