Question

我正在尝试在单独的类中实现object CancelAfterTimer class CancelAfter[T](getTimeout: T => FiniteDuration) extends GraphStage[FlowShape[T, T]] { val in = Inlet[T]("CancelAfter.in") val out = Outlet[T]("CancelAfter.in") override val shape: FlowShape[T, T] = FlowShape(in, out) override def createLogic(inheritedAttributes: Attributes): GraphStageLogic = new TimerGraphStageLogic(shape) with InHandler with OutHandler { override def onPush(): Unit = { val elem = grab(in) if (!isTimerActive(CancelAfterTimer)) scheduleOnce(CancelAfterTimer, getTimeout(elem)) push(out, elem) } override def onTimer(timerKey: Any): Unit = completeStage() //this will cancel the upstream and close the downstrean override def onPull(): Unit = pull(in) setHandlers(in, out, this) } }，但它没有工作：

UITextFieldDelegate

但这有效：

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
    }
}

有什么问题吗？

Answer 1

UITextField的{{3}}是弱属性，因此在viewDidLoad方法结束时， 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ValidationTextField.delegate中打印viewDidAppear(animated:)，然后看到它返回nil。

要解决此问题，您可以将restrictor定义为实例变量，只要视图控制器处于活动状态，它就会保持活动状态：

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

  let restrictor = TextFieldRestrictController()

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

如何在Swift中的单独类中设置UITextField的委托？

1 个答案: