Ios 尝试将变量从一个类移动到另一个类

我目前正在尝试将一个变量从一个类移动到另一个类。我正在使用

AVFramework

读取二维码。QR码最终读取字符串变量，然后字符串变量读取label.text。我想在另一个类的textview中使用完全相同的文本

QRScannerController

包含QR代码，而

HistoryView

是我想重复使用变量的地方。问题是，一旦我扫描二维码并移动到历史视图，它什么也看不到。这是我到目前为止所拥有的。下面是

QRScannerController

func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?){   
    if segue.destination .isKind(of:HistoryView.self){
        let vc2 = segue.destination as! HistoryView
        vc2.previousViewController = self
    }
}

@IBOutlet var messageLabel:UILabel!
@IBOutlet var topbar: UIView!
@IBOutlet var segmentedControl: UISegmentedControl!
//@IBOutlet var textFacts: UITextView!


var captureSession:AVCaptureSession?
var videoPreviewLayer:AVCaptureVideoPreviewLayer?
var qrCodeFrameView:UIView?



let supportedCodeTypes = [AVMetadataObjectTypeUPCECode,
                    AVMetadataObjectTypeCode39Code,
                    AVMetadataObjectTypeCode39Mod43Code,
                    AVMetadataObjectTypeCode93Code,
                    AVMetadataObjectTypeCode128Code,
                    AVMetadataObjectTypeEAN8Code,
                    AVMetadataObjectTypeEAN13Code,
                    AVMetadataObjectTypeAztecCode,
                    AVMetadataObjectTypePDF417Code,
                    AVMetadataObjectTypeQRCode]

@IBAction func unwindToHomeScreen(segue: UIStoryboardSegue) {
    dismiss(animated: true, completion: nil)
}

override func viewDidLoad() {
    super.viewDidLoad()



    // Get an instance of the AVCaptureDevice class to initialize a device object and provide the video as the media type parameter.
    let captureDevice = AVCaptureDevice.defaultDevice(withMediaType: AVMediaTypeVideo)

    do {
        // Get an instance of the AVCaptureDeviceInput class using the previous device object.
        let input = try AVCaptureDeviceInput(device: captureDevice)

        // Initialize the captureSession object.
        captureSession = AVCaptureSession()

        // Set the input device on the capture session.
        captureSession?.addInput(input)

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

        // Set delegate and use the default dispatch queue to execute the call back
        captureMetadataOutput.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
        captureMetadataOutput.metadataObjectTypes = supportedCodeTypes

        // 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()

        // Move the message label and top bar to the front
        view.bringSubview(toFront: messageLabel)
        view.bringSubview(toFront: topbar)

        // Initialize QR Code Frame to highlight the QR code
        qrCodeFrameView = UIView()

        if let qrCodeFrameView = qrCodeFrameView {
            qrCodeFrameView.layer.borderColor = UIColor.green.cgColor
            qrCodeFrameView.layer.borderWidth = 2
            view.addSubview(qrCodeFrameView)
            view.bringSubview(toFront: qrCodeFrameView)
        }

    } catch {
        // If any error occurs, simply print it out and don't continue any more.
        print(error)
        return
    }

}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}



// MARK: - AVCaptureMetadataOutputObjectsDelegate Methods

public func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [Any]!, from connection: AVCaptureConnection!) {

    // Check if the metadataObjects array is not nil and it contains at least one object.
    if metadataObjects == nil || metadataObjects.count == 0 {
        qrCodeFrameView?.frame = CGRect.zero
        //messageLabel.text = "No QR/barcode is detected"
        return
    }


    // Get the metadata object.
    let metadataObj = metadataObjects[0] as! AVMetadataMachineReadableCodeObject


    if 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
        let barCodeObject = videoPreviewLayer?.transformedMetadataObject(for: metadataObj)
        qrCodeFrameView?.frame = barCodeObject!.bounds

         if metadataObj.stringValue != nil {
            //captureSession?.stopRunning()

            messageLabel.text = metadataObj.stringValue
            messageLabel.text = messageLabel.text

            //let vc: UINavigationController = storyboard?.instantiateViewController(withIdentifier: "View") as! UINavigationController


            let vc3: UIViewController = storyboard!.instantiateViewController(withIdentifier: "View") //as! UIViewController

            self.present(vc3, animated: true, completion: nil)

        }
    }
}
func transferViewControllerVariables() -> (UILabel){
    return messageLabel
}
}

以下是历史视图：

import UIKit
import AVFoundation

class HistoryView: UIViewController, AVCaptureMetadataOutputObjectsDelegate {

    @IBOutlet var textHistory:UITextView!
    var previousViewController: QRScannerController?


    @IBAction func unwindToHomeScreen(segue: UIStoryboardSegue) {
        dismiss(animated: true, completion: nil)
    }

    @IBAction func toMaps(segue: UIStoryboardSegue) {
        let vc3: UIViewController = storyboard!.instantiateViewController(withIdentifier: "front") //as! UIViewController

        self.present(vc3, animated: true, completion: nil)
    }


    override func viewDidLoad() {
            super.viewDidLoad()
            // Do any additional setup after loading the view.


        let  messageLabel = previousViewController?.transferViewControllerVariables()
        //print(messageLabel.text as Any)
        textHistory.text = messageLabel?.text

        }

        // Do any additional setup after loading the view.


    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}

---

您应该在

HistoryView

中声明

messageLabel

。执行segue时，分配值，就这样

class HistoryView: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
    var messageLabel: String?

}



class QRCodeScanner: UIViewController {
    func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?){   
        if segue.destination.isKind(of:HistoryView.self){
            if let vc2 = segue.destination as? HistoryView {
                vc2.messageLabel = self.messageLabel.text
            }
        }
    }
}

---

我建议您将实际文本传递给下一个视图控制器，而不是整个上一个视图控制器。 但一般的问题是永远不会调用prepareForSegue函数，因为HistoryView控制器不是通过segue显示的，而是通过编程方式显示的

要以编程方式将数据传递给HistoryView控制器，请在QRScannerViewController的captureOutput函数中执行此操作：

let vc3: HistoryView = storyboard!.instantiateViewController(withIdentifier: "View") as! HistoryView
vc3.messagetext = metadataObj.stringValue
self.present(vc3, animated: true, completion: nil)

要在历史记录中添加新属性，请执行以下操作：

class HistoryView: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
    var messageText: String?
}

---

然后可以完全删除prepareForSegue函数，因为它没有被调用。

为什么不使用segue，而是在

QRScannerController

中使用

present

和

vc3

？只需将其更改为

performsgue

，然后它就可以工作了。这可能会有帮助。首先，QRCodeScanner中的第二条if语句无效，并导致错误。其次，我得到错误“QRScannerController类型的值没有成员messageLabel”，它应该是您的

@IBOutlet var messageLabel:UILabel是！！我已经这样做并让它执行了，但是文本显示为空。您是否将textHistoryText分配给messageText，如下所示：textHistory.text=messageText？当您到达prepareForReuse时，是否设置了messageLabel上的文本？是的，我已指定了文本。我最后有准备功能。这是在切换到新视图之后，因此此时应该设置消息标签。它仍然什么也看不见。这使我确信数据不会传输到另一个类。但是您确实在prepareForSegue中到达了这一行：vc2.messageText=self.messageLabel.text？我如何知道是否确实到达了这一行？