ObjC(Category of NSString)：

- (CGSize)getSizeWithFont:(UIFont *)font constrainedToSize:(CGSize)size{    CGSize resultSize = CGSizeZero;    if (self.length <= 0) {        return resultSize;    }    NSMutableParagraphStyle *style = [NSMutableParagraphStyle new];    style.lineBreakMode = NSLineBreakByWordWrapping;    resultSize = [self boundingRectWithSize:CGSizeMake(floor(size.width), floor(size.height))//用相对小的 width 去计算 height / 小 heigth 算 width                                    options:(NSStringDrawingUsesFontLeading | NSStringDrawingUsesLineFragmentOrigin)                                 attributes:@{NSFontAttributeName: font,                                              NSParagraphStyleAttributeName: style}                                    context:nil].size;    resultSize = CGSizeMake(floor(resultSize.width + 1), floor(resultSize.height + 1));//上面用的小 width（height） 来计算了，这里要 +1    return resultSize;}

 

 

Swift(Extension of NSString):

func getSizeWithFont(_ font:UIFont,constrainedToSize size:CGSize) -> CGSize{                if self.length == 0 { return CGSize.zero }                let style = NSMutableParagraphStyle.init()        style.lineBreakMode = .byWordWrapping                let options = NSStringDrawingOptions.usesFontLeading.union(.usesLineFragmentOrigin)        let attributes = [NSFontAttributeName:font,NSParagraphStyleAttributeName:style]        let bound = CGSize.init(width: floor(size.width), height: floor(size.height))                let rect = self.boundingRect(with: bound, options: options, attributes: attributes, context: nil)        let _size = CGSize.init(width: floor(rect.width + 1), height: floor(rect.height + 1))                return _size    }