Question

我想将ItemID的值设为全局，以便我可以在函数旁边访问它。我试图在类下面定义它但它不起作用。我怎样才能在其他函数可以访问的函数中创建一个值？

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

        if metadataObj.stringValue != nil {
            messageLabel.text = metadataObj.stringValue
            //Searches firebase for existing barcode
            }
            let itemID = metadataObj.stringValue!
            let itemToSearchFor = itemID

            guard let Description = productDescriptionTextField.text,
            let price = priceTextField.text,
            let location = productLocationTextField.text
            else{
                print("Fill basic product information")
                return
             }
            let ref = FIRDatabase.database().reference(fromURL: "/")
            // creating an  item child node
            let values = ["Item Description": Description, "Image": price, "Location": location, "Price": price]
            let items = ref.child("Items").child(itemID)
            items.updateChildValues(values, withCompletionBlock: { (err, ref) in
                if err != nil {
                    print(err)
                    return
                } })
             FIRDatabase.database().reference().child("Items").child(itemToSearchFor).observeSingleEvent(of: .value, with:{(snap) in
                    print(snap)
                        })
    }}

这是我想调用itemID

的功能

 func enterNewProduct() {

    guard let Description = self.productDescriptionTextField.text,
        let price = self.priceTextField.text,
        let location = self.productLocationTextField.text
        else{
            print("Fill basic product information")
            return
    }

    let ref = FIRDatabase.database().reference(fromURL: "/")
    // creating an  item child node
    let values = ["Item Description": Description, "Image": price, "Location": location, "Price": price ]
    let items = ref.child("Items").child(itemID)
    items.updateChildValues(values, withCompletionBlock: { (err, ref) in
        if err != nil {
            print(err)
            return
        } })


    self.dismiss(animated: true, completion: nil)

}

由于某种原因，它无法识别上一个函数的itemID

Answer 1

将它放在像这样的函数上面。

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

然后在你的功能中你应该能够像这样访问它。

itemID = metadataObj.stringValue!
let itemToSearchFor = itemID

请务必使用var以便修改。

Answer 2

听起来你已经做好了一切。您忘记将代码放在“试图在类下面定义它”的位置。如果这是问题，这里有一个有效的模板：

class ViewController: UIViewController {

    var myID = "ID #1"

    override func viewDidLoad() {
        super.viewDidLoad()
        changeID()
        printID()
    }
    func changeID() {
        printID()
        myID = "ID #2"
    }
    func printID() {
        print(myID)
    }
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

控制台输出是：

ID #1
ID #2

如何在函数全局中创建一个值

2 个答案: