有没有一种方法可以将 lineSpacing
对象的 NSParagraphStyle
/ NSMutableParagraphStyle
属性的 NSAttributedString
属性设置为字体的基础/原始lineSpacing
的百分比?lineSpacing
是NSParagraphStyle
的属性,而不是UIFont
,因此无法知道字体的原始lineSpacing
是什么。
作为参考,这是我写的一些扩展,用于将lineSpacing
分配给UILabel
(累积的,不会导致标签的attributedString丢失信息):
import UIKit
extension UILabel {
/// -important: must be called after setting the `text` property so the computed NSRange would be valid
func setLineSpacing(with lineSpacing: CGFloat) {
// get safe string
guard let textString = self.text, !textString.isEmpty
else { return }
// get the range
let entireRange: NSRange = (textString as NSString).range(of: textString)
guard entireRange.isValidNSRange(within: textString)
else { assertionFailure() ; return }
// NSMutableAttributedText
guard let mutableAttributedText: NSMutableAttributedString = self.attributedText?.mutableCopy() as? NSMutableAttributedString
else { assertionFailure() ; return }
// NSParagraphStyle
var paragraphStyle: NSParagraphStyle? = mutableAttributedText.attribute(NSParagraphStyleAttributeName, at: 0, longestEffectiveRange: nil, in: entireRange) as? NSParagraphStyle
if paragraphStyle == nil {
// why TTTAttributedLabel :(
paragraphStyle = NSParagraphStyle()
}
// safe NSParagraphStyle
guard let safeParagraphStyle: NSParagraphStyle = paragraphStyle
else { assertionFailure() ; return }
// NSMutableParagraphStyle
guard let mutableParagraphStyle: NSMutableParagraphStyle = safeParagraphStyle.mutableCopy() as? NSMutableParagraphStyle
else { assertionFailure() ; return }
// this is where the magic happens
mutableParagraphStyle.lineSpacing = lineSpacing
mutableAttributedText.addAttribute(NSParagraphStyleAttributeName, value: mutableParagraphStyle, range: entireRange)
// assign attributed text which has all the existing attributes plus the new line spacing attribute which is inside the paragraphstyle attribute...
self.attributedText = mutableAttributedText
}
}
extension NSRange {
// Is it safe to use range on the string?
func isValidNSRange(within string: String) -> Bool {
if self.location != NSNotFound
&& self.length > 0
&& self.location + self.length - 1 < string.length
&& self.location >= 0
{
return true
} else {
return false
}
}
}
我已经研究了问题,在Stackoverflow上找不到答案。所以我要分享自己的FWIW。 (我想添加
CoreText
标记,以便可以轻松搜索,但是我的声誉不允许我) 最佳答案
解
extension UIFont {
func getLineSpacing(with percentage: CGFloat = 1) -> CGFloat {
let lineSpacing: CGFloat = (self.lineHeight - self.pointSize)// /2
return lineSpacing * percentage
}
}
我基于解决方案this article和this interesting Chinese article。更具体地说,我将附上我用来推断答案的部分的屏幕截图: