关于 UITableViewCell 重用的问题

我在做一个类似于微信朋友圈一样的，复杂的 UITableViewCell

在 UITableViewCell 的init(style: UITableViewCellStyle, reuseIdentifier: String?)里，我先创建好所有要用的控制，比如头像、昵称、内容、图片的容器等。

然后通过一个 setModal 的方法去设置每个 cell 不同的数据， setModal 会在 cellForRowAt 里调用，

而 setModal 里会根据图片的情况显示或隐藏图片的容器。同时更新所有相关视图 AutoLayout 的 top

内容有些只有图片，有些只有文字内容，而有些同时拥有文字跟图片，开始的一屏没问题，往下滚动后，新出来的 cell 也没什么问题，

但当重新往上滚的时候，重新出来的上面的 cell 布局乱了。

我用的是 SnapKit ，乱了布局的 cell 报了Unable to simultaneously satisfy constraints的错。

我检查了我的代码，在 setModal 里，如果有要显示的内容，我就新 makeConstraints ，而一般都是新加一个 top 的约束，如果不需要显示，就把缓存了的 top 约束 deactivate ，并 isHidden=true 掉。

所以我在怀疑，是不是 UITableViewCell 的重用问题， UITableViewCell 的重用不是拿缓存里的 cell 来用的吗？

如果一个 cell 我先用过了，并设置了图片、文字的视图是显示状态的，下一次被调用的时候，他们应该也是显示的，

所以我需要根据内容再做一次显示 /隐藏的动作。那文字呢？我的内容是通过 attributedText 设置的，第一次加载 的时候是正确的，但先往下滚，再往上滚的时候，就不对了，文字的框明显就高了，所以原来对的约束逻辑，就会被“尝试打破约束”这样的错。是不是有什么办法能让显示内容的 label 高度也刷新一下？

而且我还作了另一种尝试，就是把可能会发生隐藏或显示的视图的约束，在setModal里全部重新做一遍， 就是根据数据，如果这个视图是隐藏的，我就直接removeConstraints，下次如果显示，我也先removeConstraints 然后再makeConstraints 把全部约束重新加一遍，显示是对了，但还是会报“尝试打破约束”的打，不知道到底是哪不对

import UIKit
import SnapKit

class CircleCell: UITableViewCell {
var avatar                      : UIView!;
var nickname                    : UILabel!;
var downArrow                   : UILabel!;
var timeLabel                   : UILabel!;
var contentLabel                : UILabel!;
var likeBtn                     : UIButton!;
var commentBtn                  : UIButton!;
var expandLabel                 : UILabel!;
var imageBox                    : ImageCell!;
var pageBox                     : PageCell!;

var contentTopConstraint     : Constraint?;
var expandTopConstriaint     : Constraint?;
var imageBoxTopConstrint     : Constraint?;

override init(style: UITableViewCellStyle, reuseIdentifier: String?) {
    super.init(style: style, reuseIdentifier: reuseIdentifier);
    self.selectionStyle = .none;
    
    self.setUp();
}

required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
}

fileprivate func setUp(){
    self.contentView.layer.shouldRasterize = true;
    self.contentView.isOpaque = true;
    self.layer.shouldRasterize = true;
    self.isOpaque = true;
    
    avatar = UIView();
    avatar.isUserInteractionEnabled = true;
    avatar.backgroundColor = .red;
    
    nickname = UILabel();
    nickname.sizeToFit();
    nickname.numberOfLines = 1;
    nickname.font = UIFont.boldSystemFont(ofSize: Dimens.COMMON_FONT_SIZE);
    nickname.textColor = Colors.MainYellow;
    
    expandLabel = UILabel();
    expandLabel.sizeToFit();
    expandLabel.numberOfLines = 1;
    expandLabel.textColor = Colors.MainYellow;
    expandLabel.isUserInteractionEnabled = true;
    expandLabel.font = UIFont.systemFont(ofSize: Dimens.COMMON_FONT_SIZE);
    
    contentLabel = UILabel();
    contentLabel.numberOfLines = 0;
    contentLabel.font = UIFont.systemFont(ofSize: Dimens.COMMON_FONT_SIZE);
    contentLabel.textColor = Colors.MAIN_BLACK;
    contentLabel.backgroundColor = .brown;
    
    downArrow = UILabel();
    downArrow.sizeToFit();
    downArrow.textAlignment = .right;
    let arrowStr = FontAwesome.icon("fa-angle-down");
    let arrowAttribute = NSMutableAttributedString(string: arrowStr);
    let arrowFont = UIFont(name: Fonts.FontAwesome, size: Dimens.MATERIAL_ICON_SIZE);
    arrowAttribute.addAttribute(NSFontAttributeName, value: arrowFont!, range: NSMakeRange(0, 1));
    arrowAttribute.addAttribute(NSForegroundColorAttributeName, value: Colors.COLOR9ea1ab, range: NSMakeRange(0, 1));
    downArrow.attributedText = arrowAttribute;
    downArrow.isUserInteractionEnabled = true;
    
    timeLabel = UILabel();
    timeLabel.sizeToFit();
    timeLabel.numberOfLines = 1;
    timeLabel.font = UIFont.systemFont(ofSize: Dimens.SECOND_TITLE_FONT_SIZE);
    timeLabel.textColor = Colors.COLOR9ea1ab;
    timeLabel.backgroundColor = .yellow;
    
    imageBox = ImageCell();
    pageBox = PageCell();
    
    likeBtn = UIButton();
    likeBtn.contentEdgeInsets = UIEdgeInsetsMake(0.01, 0, 0.01, 0);
    
    commentBtn = UIButton();
    commentBtn.contentEdgeInsets = UIEdgeInsetsMake(0.01, 0, 0.01, 0);
    self.contentView.addSubview(self.avatar);
    self.contentView.addSubview(self.nickname);
    self.contentView.addSubview(self.downArrow);
    self.contentView.addSubview(self.timeLabel);
    self.contentView.addSubview(self.commentBtn);
    self.contentView.addSubview(self.likeBtn);
    self.contentView.addSubview(self.contentLabel);
    self.contentView.addSubview(self.expandLabel);
    self.contentView.addSubview(self.imageBox);
    self.contentView.addSubview(self.pageBox);
    layout();
}

fileprivate func layout(){
    self.avatar.snp.makeConstraints { [unowned self](make) in
        make.left.top.equalTo(self.contentView).offset(10);
        make.width.height.equalTo(40);
    }
    
    self.downArrow.snp.makeConstraints { [unowned self](make) in
        make.right.equalTo(self.contentView).offset(-10);
        make.centerY.equalTo(self.nickname);
        make.width.equalTo(40);
        make.height.equalTo(self.nickname).offset(10);
    }
    
    self.nickname.snp.makeConstraints { [unowned self](make) in
        make.left.equalTo(self.avatar.snp.right).offset(10);
        make.top.equalTo(self.avatar);
    }
    
    self.contentLabel.snp.makeConstraints{ [unowned self](make) in
        make.left.equalTo(self.nickname);
        make.right.equalTo(self.contentView).offset(-10);
    }
    
    self.expandLabel.snp.makeConstraints{ [unowned self](make) in
        make.left.equalTo(self.contentLabel);
    }
    
    self.imageBox.snp.makeConstraints{ [unowned self](make) in
        make.left.equalTo(self.contentLabel);
        make.right.equalTo(self.contentView);
    }
    
    self.pageBox.snp.makeConstraints{ [unowned self](make) in
        make.left.equalTo(self.imageBox);
        make.right.equalTo(self.contentView).offset(-10);
    }
    
    self.timeLabel.snp.makeConstraints { [unowned self](make) in
        make.left.equalTo(self.nickname);
        make.bottom.equalTo(self.contentView).offset(-10);
    }
    
    self.commentBtn.snp.makeConstraints { [unowned self](make) in
        make.right.equalTo(self.contentView).offset(-10);
        make.centerY.equalTo(self.timeLabel);
    }
    
    self.likeBtn.snp.makeConstraints { [unowned self](make) in
        make.right.equalTo(self.commentBtn.snp.left).offset(-10);
        make.centerY.equalTo(self.timeLabel);
    }
}

func setModel(data: PostStatus, sizeCache: SizeCache){
    //set up avatar
    
    self.nickname.text = data.user!.nickname;

    let content = data.content;
    var showExpand = false;
    var hasContent = false;
    var hasImage = false;
    var hasPage = false;
    if content != "" {
        hasContent = true;
        self.contentLabel.isHidden = false;
        var lines = sizeCache.visibleLines;
        if sizeCache.totalLines <= 12 {
            lines = sizeCache.totalLines;
        }else{
            showExpand = true;
        }
        
        self.contentLabel.text = content;
        self.contentLabel.numberOfLines = lines;
        self.contentLabel.snp.makeConstraints({ [unowned self](make) in
            self.contentTopConstraint = make.top.equalTo(self.nickname.snp.bottom).offset(10).constraint;
        });
        if showExpand {
            self.expandLabel.isHidden = false;
            self.expandLabel.text = "展开";
            self.expandLabel.snp.makeConstraints{ [unowned self](make) in
                self.expandTopConstriaint = make.top.equalTo(self.contentLabel.snp.bottom).offset(10).constraint;
            }
        }else{
            self.expandLabel.isHidden = true;
            self.expandTopConstriaint?.deactivate();
        }
    }else{
        self.contentTopConstraint?.deactivate();
        self.contentLabel.isHidden = true;
        self.expandTopConstriaint?.deactivate();
        self.expandLabel.isHidden = true;
    }

    let arr = [UIImage](repeating: UIImage(), count: data.images.count);
    self.imageBox.update(images: arr);
    if data.images.count > 0 {
        hasImage = true;
        self.imageBox.isHidden = false;
        if hasContent {
            if showExpand {
                self.imageBox.snp.makeConstraints({ [unowned self](make) in
                    self.imageBoxTopConstrint = make.top.equalTo(self.expandLabel.snp.bottom).offset(10).constraint;
                });
            }else{
                self.imageBox.snp.makeConstraints({ [unowned self](make) in
                    self.imageBoxTopConstrint = make.top.equalTo(self.contentLabel.snp.bottom).offset(10).constraint;
                });
            }
        }else{
            self.imageBox.snp.makeConstraints({ [unowned self](make) in
                self.imageBoxTopConstrint = make.top.equalTo(self.nickname.snp.bottom).offset(10).constraint;
            });
        }
    }else{
        self.imageBoxTopConstrint?.deactivate();
        self.imageBox.isHidden = true;
    }

    if let _ = data.game {
        hasPage = true;
        self.pageBox.snp.makeConstraints({ (make) in
            make.height.equalTo(70);
        });
        if hasImage {
            self.pageBox.snp.makeConstraints({ [unowned self](make) in
                make.top.equalTo(self.imageBox.snp.bottom).offset(10);
            });
        }else{
            if hasContent {
                if showExpand {
                    self.pageBox.snp.makeConstraints({ [unowned self](make) in
                        make.top.equalTo(self.expandLabel.snp.bottom).offset(10);
                    });
                }else{
                    self.pageBox.snp.makeConstraints({ [unowned self](make) in
                        make.top.equalTo(self.contentLabel.snp.bottom).offset(10);
                    });
                }
            }else{
                self.pageBox.snp.makeConstraints({ [unowned self](make) in
                    make.top.equalTo(self.nickname.snp.bottom).offset(10);
                });
            }
        }
    }else{
        //TODO: clear content
    }

    self.timeLabel.text = Time.sinceNow(data.created_at!);
    if hasPage {
        self.timeLabel.snp.makeConstraints({ [unowned self](make) in
            make.top.equalTo(self.pageBox.snp.bottom).offset(10);
        });
    }else{
        if hasImage {
            self.timeLabel.snp.makeConstraints({ [unowned self](make) in
                make.top.equalTo(self.imageBox.snp.bottom).offset(10);
            });
        }else{
            if hasContent {
                if showExpand {
                    self.timeLabel.snp.makeConstraints({ [unowned self](make) in
                        make.top.equalTo(self.expandLabel.snp.bottom).offset(10);
                    });
                }else{
                    self.timeLabel.snp.makeConstraints({ [unowned self](make) in
                        make.top.equalTo(self.contentLabel.snp.bottom).offset(10);
                    });
                }
            }
        }
    }
    
    let likeStr = FontAwesome.icon("fa-thumbs-o-up");
    let likeAttribute = NSMutableAttributedString(string: "\(likeStr) 0");
    let likeFont = UIFont(name: Fonts.FontAwesome, size: Dimens.COMMON_TITLE_FONT_SIZE);
    let commonFont = UIFont.systemFont(ofSize: Dimens.COMMON_TITLE_FONT_SIZE);
    var numStr = "\(data.like_num)";
    var numNum = numStr.characters.count;
    likeAttribute.addAttribute(NSFontAttributeName, value: likeFont!, range: NSMakeRange(0, 1));
    likeAttribute.addAttribute(NSFontAttributeName, value: commonFont, range: NSMakeRange(1, numNum + 1));
    likeAttribute.addAttribute(NSForegroundColorAttributeName, value: Colors.COLOR9ea1ab, range: NSMakeRange(0, numNum + 2));
    
    let likeHighlightedAttribute = NSMutableAttributedString(string: "\(likeStr) 0");
    likeHighlightedAttribute.addAttribute(NSFontAttributeName, value: likeFont!, range: NSMakeRange(0, 1));
    likeHighlightedAttribute.addAttribute(NSFontAttributeName, value: commonFont, range: NSMakeRange(1, numNum + 1));
    likeHighlightedAttribute.addAttribute(NSForegroundColorAttributeName, value: Colors.COLOReeeeee, range: NSMakeRange(0, numNum + 2));
    
    likeBtn.setAttributedTitle(likeAttribute, for: UIControlState());
    likeBtn.setAttributedTitle(likeHighlightedAttribute, for: .highlighted);
    
    let commentStr = FontAwesome.icon("fa-commenting-o");
    let commentAttribute = NSMutableAttributedString(string: "\(commentStr) 0");
    let commentFont = UIFont(name: Fonts.FontAwesome, size: Dimens.COMMON_TITLE_FONT_SIZE);
    numStr = "\(data.comment_num)";
    numNum = numStr.characters.count;
    commentAttribute.addAttribute(NSFontAttributeName, value: commentFont!, range: NSMakeRange(0, 1));
    commentAttribute.addAttribute(NSFontAttributeName, value: commentFont!, range: NSMakeRange(1, numNum + 1));
    commentAttribute.addAttribute(NSForegroundColorAttributeName, value: Colors.COLOR9ea1ab, range: NSMakeRange(0, numNum + 2));
    commentAttribute.addAttribute(NSBaselineOffsetAttributeName, value: 1, range: NSMakeRange(0, 1));
    
    let commentHighlightedAttribute = NSMutableAttributedString(string: "\(commentStr) 0");
    commentHighlightedAttribute.addAttribute(NSFontAttributeName, value: commentFont!, range: NSMakeRange(0, 1));
    commentHighlightedAttribute.addAttribute(NSFontAttributeName, value: commentFont!, range: NSMakeRange(1, numNum + 1));
    commentHighlightedAttribute.addAttribute(NSForegroundColorAttributeName, value: Colors.COLOReeeeee, range: NSMakeRange(0, numNum + 2));
    commentHighlightedAttribute.addAttribute(NSBaselineOffsetAttributeName, value: 1, range: NSMakeRange(0, 1));
    commentBtn.setAttributedTitle(commentAttribute, for: UIControlState());
    commentBtn.setAttributedTitle(commentHighlightedAttribute, for: .highlighted);
}

deinit {
    Log.verbose("\(type(of: self)) deinit");
}

}