NSLayoutConstraint约束的active属性

@property (weak, nonatomic) IBOutlet NSLayoutConstraint *commentLabelHeightCon; // 评论数量Label高度约束,在xib中，高度约束值为0
@property (weak, nonatomic) IBOutlet NSLayoutConstraint *firstCon;              // 第一个评论高度约束,在xib中，高度约束值为0
@property (weak, nonatomic) IBOutlet NSLayoutConstraint *secondCon;             // 第二个评论高度约束,在xib中，高度约束值为0


/**
 *  关注动态 - 作品数据
 */
- (void)setDish:(XCFDish *)dish {
    _dish = dish;

    [self.iconView setHeaderWithURL:[NSURL URLWithString:dish.author.photo60]];
    self.authorNameLabel.text = dish.author.name;
    self.createTimeLabel.text = dish.friendly_create_time;
    self.dishNameLabel.text = dish.name;
    self.descLabel.text = dish.desc;
    self.diggsCountLabel.text = [NSString stringWithFormat:@"%@人", dish.ndiggs];

    if (dish.is_orphan) {
        self.actionLabel.text = @"分享到";
    } else {
        self.actionLabel.text = @"做过";
    }

    self.commentCountLabel.text = @"";
    self.firstCommentLabel.text = @"";
    self.secondCommentLabel.text = @"";
    // 调整点赞按钮约束
    self.diggsButtonCon.constant = dish.commentViewHeight;

    if (dish.latest_comments.count) { // 如果有评论

        NSLog(@"self.firstCon.active==%zd", self.firstCon.active);

        // active默认值是YES,如果想自动获得UILabel的高度，把该属性设置为NO,并且给label设置文本，那么label的高度会自动计算显示出来，不需要其他处理
        // 显示第1条评论
        self.firstCon.active = NO;
        XCFComment *firstComment = [dish.latest_comments lastObject];
        [self.firstCommentLabel setAttributeTextWithString:[NSString stringWithFormat:@"%@：%@", firstComment.author.name, firstComment.txt]
                                                     range:NSMakeRange(0, firstComment.author.name.length)];

        // 如果有1条以上评论
        if (dish.latest_comments.count > 1) {

            // 显示第2条评论
            self.secondCon.active = NO;
            XCFComment *secondComment = dish.latest_comments[dish.latest_comments.count - 2];
            [self.secondCommentLabel setAttributeTextWithString:[NSString stringWithFormat:@"%@：%@", secondComment.author.name, secondComment.txt]
                                                          range:NSMakeRange(0, secondComment.author.name.length)];

//            if ([secondComment.txt rangeOfString:@"@"].location != NSNotFound) {
//
//                NSRange range1 = [secondComment.txt rangeOfString:@"@"];
//                NSRange range2 = [secondComment.txt rangeOfString:@" "];
//                NSRange result = NSMakeRange(range1.location, range2.location-range1.location);
//                XCFLog(@"%zd %zd", result.location, result.length);
//            }
            // 如果有2条以上评论
            if (dish.latest_comments.count > 2) {

                // 显示评论总数Label
                self.commentLabelHeightCon.active = NO;
                self.commentCountLabel.text = [NSString stringWithFormat:@"所有%ld条评论", (long)dish.ncomments];
            }
        }
    }

}

• 效果图: