UITextInput.characterRange(at:) 偏移了几个像素

Question

在我的 UITextView 子类中添加点击识别器后，我试图获取正在点击的字符：

var textRecognizer: UITapGestureRecognizer!
required init?(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)

    textContainer.lineFragmentPadding = 0
    textContainerInset = .zero

    textRecognizer = UITapGestureRecognizer(target: self, action: #selector(textTapped))
    textRecognizer.numberOfTapsRequired = 1
    addGestureRecognizer(textRecognizer)
}

@objc func textTapped(recognizer: UITapGestureRecognizer) {
    let location = recognizer.location(in: self)
    if let cRange = characterRange(at: location) {
        let cPosition = offset(from: beginningOfDocument, to: cRange.start)
        let cChar = text[Range(NSRange(location: cPosition, length: 1), in: text)!]
        print(cChar)
    }
}

问题是，如果我的 attributedText 是 "Hello world\nWelcome to Stack Overflow" 并且我点击字母的左侧部分，例如字母 f 的左侧，那么 characterRange(at: location) returns 前一个字母 r 而不是返回 f.

Answer 1

在我看来，characterRange(at:) 有问题：

如果你在索引 n 字符的左半部分给它一个点，它 returns 范围 (n-1, n)
如果你在索引 n 字符的右半部分给它一个点，它 returns 范围 (n, n+1)
如果你在索引 beginningOfDocument 字符的左半部分给它一个点，它 returns nil
如果你在索引 endOfDocument 字符的右半部分给它一个点，它 returns (endOfDocument, endOfDocument+1)

textInput 两端行为的差异表明某处存在错误。

它的行为类似于一种“光标位置在点”函数，这使得确定此时实际是哪个字符变得不可靠：is it光标前的字符还是光标后的字符?

closestPosition(to:) 遇到完全相同的问题。

一个可行的替代方案是 layoutManager.characterIndex(for:in:fractionOfDistanceBetweenInsertionPoints:). Credit to vacawama:

@objc func textTapped(recognizer: UITapGestureRecognizer) {
    var location = recognizer.location(in: self)
    location.x -= textContainerInset.left
    location.y -= textContainerInset.top
    let cPosition = layoutManager.characterIndex(for: location, in: textContainer, fractionOfDistanceBetweenInsertionPoints: nil)
    let cChar = text[Range(NSRange(location: cPosition, length: 1), in: text)!]
    print(cChar)
}

UITextInput.characterRange(at:) 偏移了几个像素

UITextInput.characterRange(at:) is off by a few pixels

ios

uitextview

uigesturerecognizer

uitextinput

uitextposition