Kern 属性导致 UITextview 中的性能缓慢问题

Question

我想在用户输入时设置每个字符的宽度。我使用带有键 .Kern 的 NSAttributeString 效果很好，但是当文本长度大于 1000+ 时，我触摸屏幕以将光标位置放在第一行前面并输入导致性能问题的新字符，太慢和滞后。

// Initialize once and reuse every time
lazy var paragraphStyle: NSMutableParagraphStyle = {
    let paragraphStyle = NSMutableParagraphStyle()
    paragraphStyle.lineBreakMode = .byWordWrapping
    paragraphStyle.alignment = .left
    return paragraphStyle
}()

// Initialize once and reuse every time    
lazy var alignTextAttributes: [NSAttributedString.Key: Any] = {
    return [
        .kern : 30,
        .paragraphStyle : paragraphStyle,
        .foregroundColor : UIColor.black,
    ]
}()
    
func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
    // If I want to set each characters with different kern values, how can I do that?
    alignTextAttributes[.kern] = textView.text.count.isMultiple(of: 2) ? 30 : 10

    // This is the key part
    textView.typingAttributes = alignTextAttributes

    // Allow system to control typing
    return true
}

Answer 1

这是你可以尝试的 -

// 4 (or 6 or 8) spaces (depending on font size)
let padding: String = "   "

func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
    
    var cursorLocation = textView.selectedRange.location
    if text.isEmpty {
        let deleteRange = NSRange(
            location: max(0, range.location - padding.count), 
            length: range.length + padding.count
        )
        textView.textStorage.replaceCharacters(in: deleteRange, with: text)
        cursorLocation -= deleteRange.length
    } 
    else {
        let insertRange = NSRange(
            location: range.location, 
            length: range.length + padding.count
        )
        textView.textStorage.replaceCharacters(in: insertRange, with: text.appending(padding))
        cursorLocation += insertRange.length
    }
    textView.selectedRange.location = cursorLocation
    
    return false
}