Swift计算字符串size(宽度，高度)方法

OC方法 iOS 7.0及以上

CGSize  size = [stringboundingRectWithSize:CGSizeMake(MAXFLOAT,MAXFLOAT)  options:(NSStringDrawingUsesFontLeading|NSStringDrawingTruncatesLastVisibleLine|NSStringDrawingUsesLineFragmentOrigin) attributes:attribute context:nil].size;

Swift方法 iOS 7.0及以上

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

        

        let rec:CGRect = string.boundingRect(with: size, options:NSStringDrawingOptions.usesFontLeading, attributes: [NSFontAttributeName :UIFont.systemFont(ofSize: font)], context:nil);