iOS 获取 UILabel 的宽度

/**
 *  获取高度
 *
 *  @param font  目标字体
 *  @param width 约束宽度
 *
 *  @return 目标高度
 */
- (CGFloat)ptv_heightWithFont:(UIFont *)font constrainedToWidth:(CGFloat)width {
    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(width, CGFLOAT_MAX)
                                      options:(NSStringDrawingUsesLineFragmentOrigin |
                                               NSStringDrawingTruncatesLastVisibleLine)
                                   attributes:attributes
                                      context:nil].size;
    } else {
        textSize = [self sizeWithFont:textFont
                    constrainedToSize:CGSizeMake(width, CGFLOAT_MAX)
                        lineBreakMode:NSLineBreakByWordWrapping];
    }
#else
    NSMutableParagraphStyle *paragraph = [[NSMutableParagraphStyle alloc] init];
    paragraph.lineBreakMode = NSLineBreakByWordWrapping;
    NSDictionary *attributes = @{NSFontAttributeName: textFont,
                                 NSParagraphStyleAttributeName: paragraph};
    textSize = [self boundingRectWithSize:CGSizeMake(width, CGFLOAT_MAX)
                                  options:(NSStringDrawingUsesLineFragmentOrigin |
                                           NSStringDrawingTruncatesLastVisibleLine)
                               attributes:attributes
                                  context:nil].size;
#endif
    
    return ceil(textSize.height);
}