快速检测何时按下文本框

Question

我想在按下某个文本框时采取措施。我尝试过

func textFieldDidBeginEditing(_ textField: UITextField) {

    if textField == myTextField {
        print("pressed")
    }
}

但这对我不起作用。有人有解决方案吗？谢谢

Answer 1

此函数是UITextFieldDelegate的回调。但是，只有与此相关的类连接到UITextField的委托时，才会触发该事件。

使用iOS ViewController的简单示例：

class yourViewController: UIViewController, UITextFieldDelegate
{
    /* Make sure that your variable 'myTextField' was created using an IBOutlet from your storyboard*/
    @IBOutlet var myTextField : UITextField!

    override func ViewDidLoad()
    {
         super.viewDidLoad()
         myTextField.delegate = self // here you set the delegate so that UITextFieldDelegate's callbacks like textFieldDidBeginEditing respond to events
    }



    func textFieldDidBeginEditing(_ textField: UITextField) {

    if textField == myTextField {
    print("pressed")
        }
    }

}

请确保您了解委托模式事件处理的概念，以及委托如何捕获和发布此类事件。许多Cocoa GUI组件都使用此设计。这些是有用的链接。

https://docs.swift.org/swift-book/LanguageGuide/Protocols.html

https://developer.apple.com/documentation/uikit/uitextfielddelegate

http://www.andrewcbancroft.com/2015/03/26/what-is-delegation-a-swift-developers-guide/