swift - 如何在 Swift 的单独类中设置 UITextField 的委托(delegate)？

Question

我试图在单独的类中实现 UITextFieldDelegate，但它没有工作:

class ViewController: UIViewController {

    @IBOutlet var TextField: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()
        let restrictor = TextFieldRestrictController()
        TextField.delegate = restrictor
    }
}

class TextFieldRestrictController : NSObject, UITextFieldDelegate {

    public func textField(_ textField: UITextField,
                          shouldChangeCharactersIn range: NSRange,
                          replacementString string: String) -> Bool {
        let inverseSet = NSCharacterSet(
            charactersIn:"0123456789.").inverted

        let components = string.components(separatedBy: inverseSet)

        let filtered = components.joined(separator:"")
        return string == filtered
    }
}

但这是可行的:

class ViewController: UIViewController {

    @IBOutlet var TextField: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()
        TextField.delegate = self
    }

    public func textField(_ textField: UITextField,
                          shouldChangeCharactersIn range: NSRange,
                          replacementString string: String) -> Bool {
        let inverseSet = NSCharacterSet(
            charactersIn:"0123456789.").inverted

        let components = string.components(separatedBy: inverseSet)

        let filtered = components.joined(separator:"")
        return string == filtered
    }
}

有什么问题吗？

Answer 1

UITextField 的 .delegate是一个 weak 属性，所以在 viewDidLoad 方法的末尾，restrictor 将被释放，因为周围没有其他强引用指向它所指向的对象。

您可以尝试在 viewDidAppear(animated:) 中打印出 ValidationTextField.delegate 并查看它返回 nil。

为了解决这个问题，您可以将 restrictor 定义为实例变量，这样只要 View Controller 处于事件状态，它就会保持事件状态:

class ViewController: UIViewController {
  @IBOutlet weak var ValidationTextField: UITextField!

  let restrictor = TextFieldRestrictController()

  override func viewDidLoad() {
    super.viewDidLoad()
    ValidationTextField.delegate = restrictor
  }
}