在 UITextField 占位符中输入文本时，应一次消失一个字母

Question

我创建了一个UITextfield，我想在其中添加 4 位密码，但是一旦我输入第一个数字，整个占位符就会消失。如何在输入下一个密码字母时将下三个占位符字母保留在 UITextfield 中。

这是我的截图：

Answer 1

我想试试 SeanLintern88 的解决方案，因为它听起来有点挑战。在文本字段的下划线之间应该有空格的情况下。

textField.text = "_ _ _ _"

这是我自带的解决方案，虽然写起来很有趣，但我不建议在实际项目中使用。最好尝试 4 个单独的文本字段方法:)

extension ViewController: UITextFieldDelegate {

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

        guard let text = textField.text else { return false }

        var location = range.location

        //is deleting
        if string == "" {

            guard let indexToReplace = text.index(text.startIndex, offsetBy: location, limitedBy: text.endIndex) else {
                return false
            }

            let isCharDeleted = location % 2 == 0
            //place " " or "_" depending on the position that was deleted
            let stringToReplaceWith = isCharDeleted ? "_" : " "
            let charachter = stringToReplaceWith[stringToReplaceWith.startIndex]
            textField.text?.remove(at: indexToReplace)
            textField.text?.insert(charachter, at: indexToReplace)

            var newCursorPositionOffset = location

            //deletetion occured on space " "
            if !isCharDeleted {

                guard let previousIndex = text.index(text.startIndex, offsetBy: location-1, limitedBy: text.endIndex) else {
                    return false
                }
                //delete the previous charachter
                textField.text?.remove(at: previousIndex)
                let dash = "_"
                let char = dash[dash.startIndex]

                textField.text?.insert(char, at: previousIndex)

                //correct cursor position
                newCursorPositionOffset -= 1
            }

            //move cursor position
            let newPosition = textField.position(from: textField.beginningOfDocument, offset: newCursorPositionOffset)
            textField.selectedTextRange = textField.textRange(from: newPosition!, to: newPosition!)

            return false
        }

        //is typing
        if range.location + 1 <= text.characters.count,
            let end = text.index(text.startIndex, offsetBy: location+1, limitedBy: text.endIndex),
            let start = text.index(text.startIndex, offsetBy: location, limitedBy: text.endIndex) {
            textField.text = textField.text?.replacingOccurrences(of: "_", with: string, options: .caseInsensitive, range: Range(uncheckedBounds: (lower: start, upper: end)))

            //correct the cursor position if placed on " " index
            if range.location % 2 != 0 {
                location -= 1
            }
        }

        //skip " " and move cursor to the next "_"
        if location+2 < text.characters.count {
            let newPosition = textField.position(from: textField.beginningOfDocument, offset: location+2)
            textField.selectedTextRange = textField.textRange(from: newPosition!, to: newPosition!)

        }

        return false
    }

    func textFieldDidBeginEditing(_ textField: UITextField) {
        let newPosition = textField.beginningOfDocument
        textField.selectedTextRange = textField.textRange(from: newPosition, to: newPosition)


    }
}

PS：也许可以通过更好地选择字符串操作的函数来缩短它，但仍然是一个相当不友好的解决方案。

结论：不要在家里这样做：D

Answer 2

不使用placeHolder，只需覆盖shouldChangeCharactersInRange 方法并将字符附加到字符串，直到字符串长度为4 个字符，如果您希望_ 看起来与点。

Answer 3

斯威夫特 4

这是@Denislava Shentova 答案的修改版本，我相信它可以简化为更少的代码行、修复问题并使代码更具可读性。

未完全测试

import UIKit

class YourClass: UIViewController {

    //It is also a good idea to deny users the ability to paste into this textField.

    //set up textField
    let textField : UITextField = {
        let textField = UITextField()
        // These are 'long dashes' you can replace them with whatever you would like.
        // These look best IMO.
        textField.text = "——————" //No spaces needed!
        textField.textColor = .black
        textField.textAlignment = .center
        textField.tintColor = .clear //this will hide the cursor.

        return textField
    }()

    override func viewDidLoad() {
        super.viewDidLoad()
        textField.delegate = self
        //This sets the spacing or 'Kern' of the textfield. Adjust the value: 10.0 and the fontSize to get the desired output.
        textField.defaultTextAttributes.updateValue(10.0, forKey: NSAttributedStringKey.kern.rawValue)
    }
}
extension YourClass : UITextFieldDelegate {
        func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {

        //get the current text of the textField.
        guard let text = textField.text else { return false }

        //handle backspace event.
        if string == "" {
            guard let indexToReplace = text.index(text.startIndex, offsetBy: range.location, limitedBy: text.endIndex) else { return false }
            textField.text?.remove(at: indexToReplace)
            textField.text?.insert("—", at: indexToReplace)
            //adjust cursor position
            if let newPostion = textField.position(from: textField.beginningOfDocument, offset: range.location) {
                textField.selectedTextRange = textField.textRange(from: newPostion, to: newPostion)
                return false
            }
        }
        //handle character entered event.
        if range.location + 1 <= text.count,
            let end = text.index(text.startIndex, offsetBy: range.location + 1, limitedBy: text.endIndex),
            let start = text.index(text.startIndex, offsetBy: range.location, limitedBy: text.endIndex) {
            textField.text = textField.text?.replacingOccurrences(of: "—", with: string, options: .caseInsensitive, range: Range(uncheckedBounds: (lower: start, upper: end)))
        }
        //adjust cursor position.
        if range.location + 1 < text.count {
            if let newPosition = textField.position(from: textField.beginningOfDocument, offset: range.location + 1){
                textField.selectedTextRange = textField.textRange(from: newPosition, to: newPosition)
            }
        }
        return false
    }
    //make sure to start at the begining of the textField.
    func textFieldDidBeginEditing(_ textField: UITextField) {
        let newPosition = textField.beginningOfDocument
        textField.selectedTextRange = textField.textRange(from: newPosition, to: newPosition)
    }
}