整体思路：

1.首先计算标签总长度是否超过1行，超过一行添加展开收起按钮，不超过1行原样展示
2.超过1行的话，计算添加展开按钮的位置

效果图如下：

展开默认状态效果图.png

收起状态效果图.jpg

大致代码如下：

- (void)setupScollView {
    for (UIView *view in self.tagScrollView.subviews) {
        if ([view isKindOfClass:[UILabel class]] || ([view isKindOfClass:[UIButton class]])) {
            [view removeFromSuperview];
        }
    }
    CGFloat maxWidth = kScreenWidth - 35 - 110 - 15; // 标签展示最大宽度
    CGFloat openButtonWidth = 45; // 展开按钮宽度
    CGFloat buttonHeight = 15;    // 标签高度
    CGFloat numberOfLine = 1;     // 标签总列数
    CGFloat lastRight = self.hushenImg.hidden ? 0 : 35; // 标签的左边距
    int i = 0;
    BOOL isOpen = self.companyModel.isOpenTag; // 标签展开或者收起
    // 展开按钮
    UIButton *openButton = [UIButton buttonWithType:UIButtonTypeCustom];
    openButton.titleLabel.font = kFontPingFangRegular(10);
    openButton.backgroundColor = [UIColor colorWithHexString:@"#5491FF"];
    [openButton setTitle:@"展开 " forState:UIControlStateNormal];
    [openButton setTitleColor:[UIColor colorWithHexString:@"#ECF2FF"] forState:UIControlStateNormal];
    [openButton setImage:[UIImage imageNamed:@"common_company_tag_open"] forState:UIControlStateNormal];
    openButton.layer.masksToBounds = YES;
    openButton.layer.cornerRadius = 4;
    openButton.layer.borderWidth = 0.5;
    openButton.layer.borderColor = [UIColor colorWithHexString:@"#5491FF"].CGColor;
    openButton.semanticContentAttribute = UISemanticContentAttributeForceRightToLeft;
    [openButton addTarget:self action:@selector(didOpenTags) forControlEvents:UIControlEventTouchUpInside];
    if (isOpen) {
        [openButton setTitle:@"收起 " forState:UIControlStateNormal];
        [openButton setImage:[UIImage imageNamed:@"common_company_tag_unopen"] forState:UIControlStateNormal];
    }
    openButton.adjustsImageWhenHighlighted = NO;
    NSMutableArray *tagArray = [[NSMutableArray alloc] init];
// 1.计算标签总长度
    CGFloat totalLength = lastRight;
    CGFloat isHideOpenButton = YES;
    for (NSString *tags in self.tagArray) {
        NSString *tag = [NSString stringWithFormat:@"  %@  ",tags];
        CGSize titleSize = [tag sizeWithAttributes:[NSDictionary dictionaryWithObject:kFontPingFangRegular(10) forKey:NSFontAttributeName]];
        if ([tags containsString:@"展开"]) {
            titleSize.width = openButtonWidth;
        }
        totalLength = totalLength + 10 + titleSize.width;
    }
  // 2. 判断标签长度是否超过1行
    if (totalLength - 10 > maxWidth) { // 整体超过一行; 添加展开收起；
        int p = 0;
        CGFloat lastLength = lastRight;
  // 3.计算插入位置，根据不同的场景组装数据
        for (NSString *tags in self.tagArray) {
            NSString *tag = [NSString stringWithFormat:@"  %@  ",tags];
            CGSize titleSize = [tag sizeWithAttributes:[NSDictionary dictionaryWithObject:kFontPingFangRegular(10) forKey:NSFontAttributeName]];
            if ([tags containsString:@"展开"]) {
                titleSize.width = openButtonWidth;
            }
            if ((lastLength + openButtonWidth < maxWidth) && (lastLength + 10 + titleSize.width + openButtonWidth > maxWidth)) {
                break;
            }
            lastLength = lastLength + 10 + titleSize.width;
            p++;
        }
        if (!isOpen && p != 0 && i != self.tagArray.count) { // 收起状态
            for (int i=0;i < p;i++) {
                [tagArray addObject:self.tagArray[i]];
            }
            [tagArray addObject:@"展开 "];
        } else if (isOpen) {
            [tagArray addObjectsFromArray:self.tagArray];
            [tagArray addObject:@"收起 "];
        } else {
            [tagArray addObjectsFromArray:self.tagArray];
        }
    } else {
        [tagArray addObjectsFromArray:self.tagArray];
    }
    // 4.根据不同的情况组装好数据后，插入展开按钮UI
    for (NSString *tags in tagArray) {
       UILabel *lab = [[UILabel alloc] init];
       lab.font = kFontPingFangRegular(10);
       lab.textColor = [UIColor colorWithHexString:@"#ECF2FF"];
       lab.layer.masksToBounds = YES;
       lab.layer.cornerRadius = 4;
       lab.layer.borderWidth = 0.5;
       lab.layer.borderColor = [UIColor colorWithHexString:@"#93B2F5"].CGColor;;
       lab.text = [NSString stringWithFormat:@"  %@  ",tags];
        BOOL isOpenAction = NO;
        if ([tags isKindOfClass:[NSString class]] && ([tags containsString:@"展开"] || [tags containsString:@"收起"])) {
            [self.tagScrollView addSubview:openButton];
            isOpenAction = YES;
        } else {
            [self.tagScrollView addSubview:lab];
        }
        
        CGFloat left = lastRight;
        CGSize titleSize = [lab.text sizeWithAttributes:[NSDictionary dictionaryWithObject:lab.font forKey:NSFontAttributeName]];
        if ([tags containsString:@"展开"]) {
            titleSize.width = openButtonWidth;
        }
        if (titleSize.width+lastRight> maxWidth) {
            numberOfLine++;
        }
        if (titleSize.width + lastRight > maxWidth) {
            lastRight = 0;
        }
        if (isOpenAction) {
            [openButton mas_remakeConstraints:^(MASConstraintMaker *make) {
                make.left.mas_equalTo(lastRight);
                make.top.mas_equalTo((numberOfLine - 1)*buttonHeight+(numberOfLine - 1) *10);
                make.height.mas_equalTo(15);
                make.width.mas_equalTo(openButtonWidth);
            }];
        } else {
            [lab mas_remakeConstraints:^(MASConstraintMaker *make) {
                make.left.mas_equalTo(lastRight);
                make.top.mas_equalTo((numberOfLine - 1)*buttonHeight+(numberOfLine - 1) *10);
                make.height.mas_equalTo(15);
            }];
        }
        
        lastRight = titleSize.width + lastRight + 10;
        i++;
    }
    [self.tagScrollView mas_remakeConstraints:^(MASConstraintMaker *make) {
        make.right.mas_equalTo(self.financingLabel.mas_left).offset(-15);
        make.top.mas_equalTo(self.orgCodeLabel.mas_bottom).offset(12);
        make.left.mas_equalTo(self.companyImg);
        make.height.mas_equalTo(numberOfLine*buttonHeight+(numberOfLine-1)*10);
    }];
}