如何知道何时单击十进制键盘上的删除按钮

Question

我有四个textFields，每个只需要一个字符，类似于锁定屏幕。我可以输入并从一个textField 移动到下一个textField。
问题是当我想删除并移动到上一个textField 时，我不知道何时单击了删除按钮。

我正在使用：

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool

输入并从一个textField 移动到另一个。

我如何知道何时按下了删除键？

Answer 1

编辑/更新：

Xcode 11 • Swift 5.2 或更高版本

跟进这个问题，可以在post 上找到 Swift 5 语法

---

原答案

斯威夫特 1.x

跟进 Istvan 的回答，您需要在按下 deleteBackward 时发布通知：

class DigitField: UITextField {
    override func deleteBackward() {
        super.deleteBackward()
        NSNotificationCenter.defaultCenter().postNotificationName("deletePressed", object: nil)
    }

}

然后在 viewDidLoad() 中添加一个观察者如下：

NSNotificationCenter.defaultCenter().addObserver(self, selector: "goPrevious", name: "deletePressed", object: nil)

还有你的方法：

func goPrevious() {
    if secondDigit.isFirstResponder() {
        secondDigit.enabled = false
        firstDigit.enabled = true
        firstDigit.becomeFirstResponder()
    } else if thirdDigit.isFirstResponder() {
        thirdDigit.enabled = false
        secondDigit.enabled = true
        secondDigit.becomeFirstResponder()
    } else if fourthDigit.isFirstResponder() {
        fourthDigit.enabled = false
        thirdDigit.enabled = true
        thirdDigit.becomeFirstResponder()
    }
}

选择您的文本字段并将其连接到您的 DigitField

您需要将每个文本字段连接到 IBAction（使用已发送事件编辑更改）

视图控制器代码应如下所示：

import UIKit

class ViewController: UIViewController {
    
    @IBOutlet weak var firstDigit: UITextField!
    @IBOutlet weak var secondDigit: UITextField!
    @IBOutlet weak var thirdDigit: UITextField!
    @IBOutlet weak var fourthDigit: UITextField!
    
    override func viewDidLoad() {
        super.viewDidLoad()

        NSNotificationCenter.defaultCenter().addObserver(self, selector: "goPrevious", name: "deletePressed", object: nil)
        
        firstDigit.secureTextEntry = true
        secondDigit.secureTextEntry = true
        thirdDigit.secureTextEntry = true
        fourthDigit.secureTextEntry = true

        firstDigit.keyboardType = .DecimalPad
        secondDigit.keyboardType = .DecimalPad
        thirdDigit.keyboardType = .DecimalPad
        fourthDigit.keyboardType = .DecimalPad

        firstDigit.becomeFirstResponder()
        secondDigit.enabled = false
        thirdDigit.enabled = false
        fourthDigit.enabled = false
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
    
    func goPrevious() {
        if secondDigit.isFirstResponder() {
            secondDigit.enabled = false
            firstDigit.enabled = true
            firstDigit.becomeFirstResponder()
        } else if thirdDigit.isFirstResponder() {
            thirdDigit.enabled = false
            secondDigit.enabled = true
            secondDigit.becomeFirstResponder()
        } else if fourthDigit.isFirstResponder() {
            fourthDigit.enabled = false
            thirdDigit.enabled = true
            thirdDigit.becomeFirstResponder()
        }
    }
    // You need to connect each text field to an IBAction (using sent events editing changed) – 
    @IBAction func firstChanged(sender: UITextField) {
        if let digitOne = sender.text.toInt() {
            println(digitOne)
            sender.enabled = false
            secondDigit.enabled = true
            secondDigit.becomeFirstResponder()
        } else {
            sender.text = ""
        }
    }
    
    @IBAction func secondChanged(sender: UITextField) {
        if let digitTwo = sender.text.toInt() {
            println(digitTwo)
            sender.enabled = false
            thirdDigit.enabled = true

            thirdDigit.becomeFirstResponder()
        } else {
            sender.text = ""
        }
    }
    
    @IBAction func thirdChanged(sender: UITextField) {
        if let digitThree = sender.text.toInt() {
            println(digitThree)
            sender.enabled = false
            fourthDigit.enabled = true
            fourthDigit.becomeFirstResponder()
        } else {
            sender.text = ""
        }
    }
    
    @IBAction func fourthChanged(sender: UITextField) {
        if let digitFour = sender.text.toInt() {
            println(digitFour)
            sender.enabled = false
        } else {
            sender.text = ""
        }
    }
}

Answer 2

子类 UITextField 如下：

import UIKit

class MyTextField: UITextField {
    override func deleteBackward() {
        super.deleteBackward()

        println("Delete button was tapped")
    }
}

然后将文本字段的类更改为 MyTextField。应该这样做！

Answer 3

对于类似的问题，in this answer 有一个可能的解决方案。你可以继承你的 UITextField，然后在你的子类中重写这个方法：

(BOOL)keyboardInputShouldDelete:(UITextField *)textField

如果这段代码在 Objective-C 中，它应该告诉你正确使用这个方法。

Answer 4

在函数中使用replacementString 以了解 UItextField 中发生的情况

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    if (string.length == 0) {
        //delete
    } else {
        //any other key
    }

    return YES;
}

Answer 5

希望我的回答对你有帮助：

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
    let  char = string.cStringUsingEncoding(NSUTF8StringEncoding)!
    let isBackSpace = strcmp(char, "\\b")

    if (isBackSpace == -92) {
        println("Backspace was pressed")
    }

    return true
}