ios marsonly文字的显示全文和收起

先设置文字宽度

        self.descritionLabel.preferredMaxLayoutWidth = kScreenWidth - 80 - 16

才能获取正确的文字行数，根据行数显示或隐藏按钮

         self.showButton.isHidden = descritionLabel.totalOfLines() <= 3 ? true : false

如果有按钮，点击按钮设置状态user.isExpand，根据状态来展开收起文字

            self.descritionLabel.numberOfLines = user.isExpand == true ? 0 : 3

extension获得label总行数

  /// - Returns: 总行数
    func totalOfLines() -> Int {
        
        if let attrText = self.attributedText {
            
            /// 创建CTFrame
            let setter: CTFramesetter = CTFramesetterCreateWithAttributedString(attrText)
            let path: CGMutablePath = CGMutablePath()
            path.addRect(CGRect(x: 0, y: 0, width: self.preferredMaxLayoutWidth, height: CGFloat.greatestFiniteMagnitude))
            let frame: CTFrame = CTFramesetterCreateFrame(setter, CFRangeMake(0, 0), path, nil)
            
            /// 获得CTLine数组
            let lines = CTFrameGetLines(frame)
            
            //获得行数
            let totalOfLines = CFArrayGetCount(lines)
            //Logger.log("totalOfLines: \(totalOfLines) :\(attrText.string)")
            return totalOfLines
        }
     
        return 0
    }