iOS Swift 根据宽度计算字体大小

背景:因为UI给的是背景图,要在背景图中间位置显示一个富文本Label

String宽度计算与高度计算

extension String{
    /// String的宽度计算
    /// - Parameter font: 设定字体前提
    public func widthWith(font: UIFont) -> CGFloat {
        let str = self as NSString
        return str.size(withAttributes: [NSAttributedString.Key.font:font]).width
    }
    /// String的高度计算
    /// - Parameters:
    ///   - width: 设定宽度前提
    ///   - lineSpacing: 设定行高前提
    ///   - font: 设定字体前提
    public func heightWith(width: CGFloat, lineSpacing: CGFloat = 1.5, font: UIFont) -> CGFloat {
        
        let str = self as NSString
        let paragraphStyle = NSMutableParagraphStyle.init()
        paragraphStyle.lineSpacing = lineSpacing
        let size = str.boundingRect(with: CGSize(width: width, height: CGFloat(MAXFLOAT)), options: [.usesLineFragmentOrigin,.usesFontLeading], attributes: [NSAttributedString.Key.paragraphStyle:paragraphStyle,NSAttributedString.Key.font:font], context: nil).size
        return size.height
    }
    /// String的宽度计算
    /// - Parameter font: 设定字体前提
    public func widthHeight(_ size:CGSize,font: UIFont,attributes : [NSAttributedString.Key : Any]? = nil) -> CGFloat {
        let str = self as NSString
        let s = str.boundingRect(with: size, options: [.usesLineFragmentOrigin,.usesFontLeading], attributes: [NSAttributedString.Key.font : font], context: nil).size.height
        return s
    }
}

设置富文本

//设置富文本
  func setAttrString(firstStr : String , secStr : String) -> NSAttributedString {
        let attrString = NSMutableAttributedString(string: firstStr + secStr)
        let strSubAttr1: [NSMutableAttributedString.Key: Any] = [.font: UIFont(name: "PingFangSC", size: 24) ?? UIFont.systemFont(ofSize: 24),.foregroundColor: UIColor.color(hexString: "#DD1827")]
        attrString.addAttributes(strSubAttr1, range: NSRange(location: 0, length: firstStr.count))
        //如果价格位数太多就将字体降低
        let fontSize = calculateStringWidth(code: firstStr, price: secStr)
        
        let strSubAttr2: [NSMutableAttributedString.Key: Any] = [.font: UIFont(name: "PingFangSC", size: CGFloat(fontSize)) ?? UIFont.systemFont(ofSize: CGFloat(fontSize)),.foregroundColor: UIColor.color(hexString: "#DD1827")]
        attrString.addAttributes(strSubAttr2, range: NSRange(location: firstStr.count, length: secStr.count))
        return attrString
    }

//根据宽度来计算title 字体大小
    func calculateStringWidth(code:String,price:String)-> CGFloat {
        //136是title可放置的宽度
        let standardWidth = (SCREEN_WIDTH - 30) / 345 * 136
        let codeWidth = code.widthWith(font: UIFont(name: "PingFangSC", size: 24) ?? UIFont.systemFont(ofSize: 24))
        //leftWidth是价格可放置的宽度
        let leftWidth = standardWidth - codeWidth
        var fontSize : CGFloat = 48
        repeat{
            fontSize -= 1
        } while price.widthWith(font: UIFont(name: "PingFangSC", size: fontSize) ?? UIFont.systemFont(ofSize: fontSize)) > leftWidth
        return fontSize
    }