Ios 部分保留 UITextField 中的占位符

传递到shouldChangeCharacters的范围指的是更改前文本字段的文本范围.通常使用键盘插入文本时，范围的长度为0,replacementString是您try 插入的字符.其 idea 是用新字符替换文本的空白区域，从而"插入"该字符.

因此，将该范围替换为占位符字符串的" "，将在占位符字符串中插入一个空格.

您应该在文本字段的文本上使用它，而不是对占位符字符串使用给定的范围.无论如何，这就是means的范围.

插入后，您可以通过执行以下操作来计算文本字段的新文本:

let newText = (textField.text! as NSString).replacingCharacters(in: range, with: string)

然后，将占位符字符串的前newText.count个字符替换为空格.将其设置为占位符标签的新文本.

// note that I changed this to a let, because I do not change the placeholder string
let placeHolderLabelString = "___ ___ ___"

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

    let newText = (textField.text! as NSString).replacingCharacters(in: range, with: string)

    // do not allow more text than the placeholder
    if newText.count > placeHolderLabelString.count {
        return false
    }
    
    let startIndex = placeHolderLabelString.startIndex
    let replaceableRange = startIndex..<placeHolderLabelString.index(startIndex, offsetBy: newText.count)
    let newPlaceholder = placeHolderLabelString.replacingCharacters(
        in: replaceableRange, with: String(repeating: " ", count: newText.count)
    )
    placeholderLabel.text = newPlaceholder
    return true
}

从外观上看，您还希望每3位数字自动添加空格.

要做到这一点，您需要设置textField.text:

// after the newText.count > placeHolderLabelString.count check
let spacesRemoved = newText.replacingOccurrences(of: " ", with: "")
textField.text = spacesRemoved.inserting(separator: " ", every: 3)

有关inserting(separator:every:)的实现，请参见this answer.你可以用另一种方式做这件事.

然后，代码的其余部分应该替换placeHolderLabelString的前textField.text!.count个字符，而不是newText.count.因为newText现在不再是文本字段中的文本.

let startIndex = placeHolderLabelString.startIndex

// note that I'm using textField.text instead of newText here,
// because *that* is actually the text of the text field now
let replaceableRange = startIndex..<placeHolderLabelString.index(startIndex, offsetBy: textField.text!.count)
let newPlaceholder = placeHolderLabelString.replacingCharacters(
    in: replaceableRange, with: String(repeating: " ", count: newText.count)
)
placeholderLabel.text = newPlaceholder

// the text field's text should not change, because we set it programmatically to the desired value already.
return false