static func calculateHeightToFitAttributedString(content: NSAttributedString, width: CGFloat) -> CGFloat {
return self.calculateSizeToFitAttributedString(content, width: width, height: CGFloat(FLT_MAX)).height
}
static func calculateSizeToFitAttributedString(content: NSAttributedString, width: CGFloat, height: CGFloat) -> CGSize {
return content.boundingRectWithSize(CGSizeMake(width, height), options: [NSStringDrawingOptions.TruncatesLastVisibleLine, NSStringDrawingOptions.UsesLineFragmentOrigin], context:nil).size
}
content.boundingRectWithSize计算出来的高度不准
原文：http://www.cnblogs.com/argenbarbie/p/5684298.html