如何将 UIPickerView 选定的行发送到另一个 ViewController

Question

我想将选定的 UIPickerViews 行发送到另一个视图控制器。我已将我的 UIPickerView didSelectRow 放在我的 prepare for segue 函数中。但是，选定的字符串不会进入我的下一个视图控制器。有人可以向我解释我做错了什么吗？非常感谢。

import UIKit

class LengthViewController: UIViewController, UIPickerViewDelegate, UIPickerViewDataSource, UITextFieldDelegate {


    @IBOutlet weak var lengthTextField: UITextField!
    @IBOutlet weak var lengthPickerView: UIPickerView!
    var startingUnit = ["","Feet","Inches","Nanometer","Millimeter","Meters","Kilometer","Yards","Miles"]
    var finalUnit  = ["","Feet","Inches","Nanometer","Millimeter","Meters","Kilometer","Yards","Miles"]
    var feet = Double()
    var inches = Double()
    var nanometer = Double()
    var millimeter = Double()
    var meters = Double()
    var kilometer = Double()
    var yards = Double()
    var miles = Double()

    override func viewDidLoad() {
        super.viewDidLoad()
        let tap = UITapGestureRecognizer(target: self.view, action: #selector(UIView.endEditing(_:)))
        view.addGestureRecognizer(tap)
        lengthPickerView.delegate = self
        lengthPickerView.dataSource = self
        lengthTextField.delegate = self

    }
    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {


        guard let oldText = textField.text, let r = Range(range, in: oldText) else {

            return true
        }

        let newText = oldText.replacingCharacters(in: r, with: string)
        let isNumeric = newText.isEmpty || (Double(newText) != nil)
        let numberOfDots = newText.components(separatedBy: ".").count - 1

        let numberOfDecimalDigits: Int
        if let dotIndex = newText.firstIndex(of: ".") {
            numberOfDecimalDigits = newText.distance(from: dotIndex, to: newText.endIndex) - 1
        } else {
            numberOfDecimalDigits = 0
        }

        return isNumeric && numberOfDots <= 1 && numberOfDecimalDigits <= 5
    }
    func pickerView(_ pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusing view: UIView?) -> UIView {
        var label = UILabel()
        if let v = view as? UILabel { label = v }
        label.font = UIFont (name: "System", size: 20)
        label.textColor = UIColor.white
        label.text =  startingUnit[row]
        label.text = finalUnit[row]
        label.textAlignment = .center
        return label
    }
    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 2
    }

    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        if component == 0 {
            return startingUnit.count
        }else{
            return finalUnit.count
        }
    }
    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        if component == 0 {
            return startingUnit[row]
        }else{
            return finalUnit[row]
        }
    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        let lengthOutput = segue.destination as! LengthOutputViewController


    func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
        if component == 0 {
           lengthOutput.startingLength = startingUnit[row] //This is where i try to send to next view controller
        }
        if component == 1 {
            lengthOutput.endingLength = finalUnit[row] //This is where i try to send to next view controller
        }
    }

    }

    @IBAction func calculatePressed(_ sender: Any) {
        if lengthTextField == nil {
            createAlert(title: "Missing length value", message: "Enter value")
        }else{
            performSegue(withIdentifier: "lengthOuput", sender: nil)
        }
    }

    func createAlert (title: String, message: String){
        let alert = UIAlertController(title: title, message: message, preferredStyle: UIAlertController.Style.alert)
        alert.addAction(UIAlertAction(title: "Ok", style: UIAlertAction.Style.default, handler: { (Action) in
            alert.dismiss(animated: true, completion: nil)
        }))
        self.present(alert, animated: true, completion: nil)
    }

}

Answer 1

你的 pickerview 的 didSelectRow() 应该定义在你的控制器的顶层。

当它被调用时，将要传递给另一个控制器的值存储在一个 ivar 中，然后在 prepare() 中，您可以将其分配给另一个控制器的属性。

Answer 2

我认为您应该做的第一件事是 从 prepare[=17] 中删除 您的 didSelectRow 方法=]方法，这些是不应该混用的方法。

为了修复您的代码，最好的方法是将当前的 startingLength 和 endingLength 存储在始终选择当前值的变量中，这样当按下 calculatePressed 按钮时，您将发送所选值存储在下一个视图控制器的变量中。

如何将 UIPickerView 选定的行发送到另一个 ViewController

How do I send UIPickerView selected row to another ViewController

uipickerview

swift