根据高度计算文字大小

@implementation UILabel (****)
/** * @brief 计算文字的大小 * * @param font 字体(默认为系统字体) * @param height 约束高度 */
- (CGSize)sizeWithFont:(UIFont *)font constrainedToHeight:(CGFloat)height
{
    
    UIFont *textFont = font ? font : [UIFont systemFontOfSize:[UIFont systemFontSize]];
    
    CGSize textSize;
    
#if __IPHONE_OS_VERSION_MIN_REQUIRED < 70000
    if ([self respondsToSelector:@selector(boundingRectWithSize:options:attributes:context:)]) {
    
        NSMutableParagraphStyle *paragraph = [[NSMutableParagraphStyle alloc] init];
        paragraph.lineBreakMode = NSLineBreakByWordWrapping;
        NSDictionary *attributes = @{
    NSFontAttributeName: textFont,
                                     NSParagraphStyleAttributeName: paragraph};
        textSize = [self boundingRectWithSize:CGSizeMake(CGFLOAT_MAX, height)
                                      options:(NSStringDrawingUsesLineFragmentOrigin |
                                               NSStringDrawingTruncatesLastVisibleLine)
                                   attributes:attributes
                                      context:nil].size;
    } else {
    
        textSize = [self sizeWithFont:textFont
                    constrainedToSize:CGSizeMake(CGFLOAT_MAX, height)
                        lineBreakMode:NSLineBreakByWordWrapping];
    }
#else
    NSMutableParagraphStyle *paragraph = [[NSMutableParagraphStyle alloc] init];
    paragraph.lineBreakMode = NSLineBreakByWordWrapping;
    NSDictionary *attributes = @{
    NSFontAttributeName: textFont,
                                 NSParagraphStyleAttributeName: paragraph};
    textSize = [self.text boundingRectWithSize:CGSizeMake(CGFLOAT_MAX, height)
                                  options:(NSStringDrawingUsesLineFragmentOrigin |
                                           NSStringDrawingTruncatesLastVisibleLine)
                               attributes:attributes
                                  context:nil].size;
#endif
    
    return CGSizeMake(ceil(textSize.width), ceil(textSize.height));
}

@end