ios swift 获取文字的长度，一般用于获取label的长度

func getTextWidth(string:String,font:CGFloat,height:CGFloat,lineSpace:CGFloat) ->CGFloat{

    let font =UIFont.systemFont(ofSize: font)

    let size = CGSize(width: CGFloat(MAXFLOAT), height: height)

    let paragraphStyle = NSMutableParagraphStyle()

    paragraphStyle.lineSpacing = lineSpace

    let attributes = [NSAttributedString.Key.font:font, NSAttributedString.Key.paragraphStyle:paragraphStyle.copy()]

    let text = string as NSString

    let rect = text.boundingRect(with: size, options:.usesLineFragmentOrigin, attributes: attributes, context:nil)

    return rect.size.width

}