ios - 自定义条码扫描仪，无法传回扫描数据

Question

我无法传回由我的自定义条码扫描器扫描的数据。数据已成功读取，我可以将值分配给变量。但是我无法将数据传回之前的 View Controller 来填充 TextView 。

我在下面使用它传递给我的条形码 VC 以将数据存储在其中

var barcodeScanData: String = ""

我在下面使用 prepare for segue

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "BarcodeScanVC" {
        let desitnationVC = segue.destination as! BarcodeScanVC
        desitnationVC.xyz = barcodeScanData
    }
}

下面是我尝试从我的自定义条码扫描仪发回数据的地方

var xyz: String = ""

func launchApp(barcodeScan: String) {

        if presentedViewController != nil {
            return
        }

        let alertPrompt = UIAlertController(title: "Barcode Found", message: "\(barcodeScan)", preferredStyle: .actionSheet)
        let confirmAction = UIAlertAction(title: "Confirm", style: UIAlertAction.Style.default, handler: { (action) -> Void in
            let barcodeData = PartsVCDetail()
            self.xyz = barcodeScan
            barcodeData.barcodeScanData = self.xyz
            print(self.xyz, "This is what I am sending")
            print(barcodeData.barcodeScanData, "This is what I am sending it TO" )


            self.navigationController?.popViewController(animated: true)
        })

        let cancelAction = UIAlertAction(title: "Cancel", style: UIAlertAction.Style.cancel, handler: nil)

        alertPrompt.addAction(confirmAction)
        alertPrompt.addAction(cancelAction)

        present(alertPrompt, animated: true, completion: nil)
    }

两条打印线

print(self.waybill, "This is what I am sending")
print(barcodeData.barcodeScanData, "This is what I am sending it TO"

但是，当我使用下面的最后一行时，显示正确的扫描数据:

self.navigationController?.popViewController(animated: true)

数据丢失，我在第一个 View Controller 的 viewDidAppear 中看到一个空值:

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(true)
    print(barcodeScanData, "This is empty but it shouldnt be")
    dataFromBarcodeScanner.text = barcodeScanData
}

我错过了什么？

Answer 1

使用此代码 let barcodeData = PartsVCDetail() 您将创建一个新的 PartsVCDetail 实例，然后设置该实例的属性。一旦操作结束，该实例将被释放，您将通过 popViewController 返回到之前的 View Controller 。

您的需求的常见解决方案是委托(delegate)模式。

• 您声明一个协议(protocol)供您的代表实现
• 您让原始 View Controller 实现此委托(delegate)协议(protocol)
• 您将原始 View Controller 设置为第二个 View Controller 的委托(delegate)
• 第二个 View Controller 可以调用委托(delegate)方法将数据传回

协议(protocol)

protocol BarcodeScanDelegate {
    func didScan(barcodeData: String)
}

零件VCDetail

class PartsVCDetail: UIViewController, BarcodeScanDelegate {

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if let desitnationVC = segue.destination as? BarcodeScanVC {
            desitnationVC.delegate = self
        }
    }

    func didScan(barcodeData: String) {
        self.barcodeScanData = barcodeData
    }
}

条码扫描VC

var delegate: BarcodeScanDelegate?

func launchApp(barcodeScan: String) {

    guard presentedViewController == nil else {
        return
    }

    let alertPrompt = UIAlertController(title: "Barcode Found", message: "\(barcodeScan)", preferredStyle: .actionSheet)
    let confirmAction = UIAlertAction(title: "Confirm", style: UIAlertAction.Style.default, handler: { (action) -> Void in
        self.delegate?.didScan(barcodeData: self.xyz)
        self.navigationController?.popViewController(animated: true)
    })

    let cancelAction = UIAlertAction(title: "Cancel", style: UIAlertAction.Style.cancel, handler: nil)

    alertPrompt.addAction(confirmAction)
    alertPrompt.addAction(cancelAction)

    present(alertPrompt, animated: true, completion: nil)
}