前言
对于swift 还处于摸索阶段很多语法还不熟悉，本文主要给大家介绍的是关于利用Swift计算文本size的相关内容，分享出来供大家参考学习，下面话不多说了，来一起看看详细的介绍吧。
iOS 11之前限制宽高计算字符串的size用的是UILabel的textRect(forBounds bounds: CGRect, limitedToNumberOfLines numberOfLines: Int) -> CGRect方法，当时也没考虑线程安全问题（low爆了），Xcode也没提示，用了好几个版本，所幸一直都没问题。
贴下方法（当时为什么选这个方法就不解释了）：
func textSize(font: UIFont, constrainedSize: CGSize, lineSpacing: CGFloat?, lines: Int) -> CGSize {
if self.isEmpty || lines < 0 {
return CGSize.zero
}
let attributedString = NSMutableAttributedString(string: self)
let range = NSRange(location: 0, length: attributedString.length)
attributedString.addAttributes([NSFontAttributeName: font], range: range)
if lineSpacing != nil {
let paragraphStyle = NSMutableParagraphStyle()
paragraphStyle.lineBreakMode = .byTruncatingTail
paragraphStyle.lineSpacing = lineSpacing!
attributedString.addAttribute(NSParagraphStyleAttributeName, value: paragraphStyle, range: range)
}
let calculatedLabel = UILabel()
calculatedLabel.font = font
calculatedLabel.attributedText = attributedString
calculatedLabel.numberOfLines = lines
let rect = calculatedLabel.textRect(forBounds: CGRect(x: 0, y: 0, width: constrainedSize.width, height: constrainedSize.height), limitedToNumberOfLines: lines)
return rect.size
}
最近升级了Xcode 9，运行时警告我let calculatedLabel = UILabel()要在主线程执行，这时才意识到问题的严重性，马上进行了修改：
extension String {
func boundingRect(with constrainedSize: CGSize, font: UIFont, lineSpacing: CGFloat? = nil) -> CGSize {
let attritube = NSMutableAttributedString(string: self)
let range = NSRange(location: 0, length: attritube.length)
attritube.addAttributes([NSAttributedStringKey.font: font], range: range)
if lineSpacing != nil {
let paragraphStyle = NSMutableParagraphStyle()
paragraphStyle.lineSpacing = lineSpacing!
attritube.addAttribute(NSAttributedStringKey.paragraphStyle, value: paragraphStyle, range: range)
}
let rect = attritube.boundingRect(with: constrainedSize, options: [.usesLineFragmentOrigin, .usesFontLeading], context: nil)
var size = rect.size
if let currentLineSpacing = lineSpacing {
// 文本的高度减去字体高度小于等于行间距，判断为当前只有1行
let spacing = size.height - font.lineHeight
if spacing <= currentLineSpacing && spacing > 0 {
size = CGSize(width: size.width, height: font.lineHeight)
}
}
return size
}
func boundingRect(with constrainedSize: CGSize, font: UIFont, lineSpacing: CGFloat? = nil, lines: Int) -> CGSize {
if lines < 0 {
return .zero
}
let size = boundingRect(with: constrainedSize, font: font, lineSpacing: lineSpacing)
if lines == 0 {
return size
}
let currentLineSpacing = (lineSpacing == nil) ? (font.lineHeight - font.pointSize) : lineSpacing!
let maximumHeight = font.lineHeight*CGFloat(lines) + currentLineSpacing*CGFloat(lines - 1)
if size.height >= maximumHeight {
return CGSize(width: size.width, height: maximumHeight)
}
return size
}
}
