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swift - 再次推送 VC 后约束被打破

问题描述

当我弹出 VC 时，我的约束被打破了。我有表格视图，当我第一次推送表格视图时，约束工作得很好，但是在再次弹出和推送之后它们就坏了。第一张图片运行良好，但第二张图片坏了也许问题出在 didSet 中，在打破约束后 xcode 说要删除宽度，但 ui 会不好 这是我的单元格代码这工作正常 这是坏了 

    var isIncoming: Bool! {
        
        didSet {
            bubbleBackgroundView.backgroundColor = isIncoming ? Constants.Color.inComingMessages : Constants.Color.outComingMessages
            messageLabel.textColor = isIncoming ? .black : .white
            
            if isIncoming {
                bubbleBackgroundView.snp.makeConstraints { (make) in
                    make.leading.equalTo(16)
                    make.width.equalTo(180)
                }
                messageLabel.snp.makeConstraints { (make) in
                    make.leading.equalTo(16)
                }
                addSubview(inComingImgTail)
                inComingImgTail.snp.makeConstraints { (make) in
                    make.trailing.equalTo(bubbleBackgroundView.snp.leading).offset(12)
                    make.top.equalTo(bubbleBackgroundView.snp.top).offset(1)
                    make.width.equalTo(15)
                    make.height.equalTo(36)
                }
            }
            else if !isIncoming{
                bubbleBackgroundView.snp.makeConstraints { (make) in
                    make.trailing.equalTo(self).offset(-16)
                    make.width.equalTo(180)
                }
                messageLabel.snp.makeConstraints { (make) in
                    make.leading.equalTo(16)
                    make.trailing.equalTo(-16)
                }
                
                addSubview(OutComingImgTail)
                OutComingImgTail.snp.makeConstraints { (make) in
                    make.trailing.equalTo(bubbleBackgroundView.snp.trailing).offset(4)
                    make.top.equalTo(bubbleBackgroundView.snp.top).offset(1)
                    make.width.equalTo(15)
                    make.height.equalTo(36)
                }
            }
        }
        
    }

这是我的数据源和委托代码


extension ChatVC: UITableViewDelegate, UITableViewDataSource {
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return ChatVC.messagesList.count

    }
    
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: MessagesCell.reuseIdentifier, for: indexPath) as! MessagesCell
        

        let messages = ChatVC.messagesList[indexPath.row]
        
        let sorted = ChatVC.messagesList.sorted { (first, second) -> Bool in
            return first.pk < second.pk
        }
        cell.messagesLists = messages
        cell.messageLabel.text = sorted[indexPath.row].text
        
        
        if sorted[indexPath.row].from_user == userID {
            cell.isIncoming = false
            
        }
        else if sorted[indexPath.row].from_user != userID {
            cell.isIncoming = true
            
        }
        
        return cell
    }
    
    
}

标签： swiftuitableviewconstraintssnapkit

解决方案

每次都重复使用单元格，并且要将模式从 .sent 切换到 .received，您必须停用以前的约束。为两种状态添加两个约束数组，并停用前一个数组并激活新数组。在您的情况下，您只需附加约束，但不要删除它们

var receivedConstraints = [NSLayoutConstraint]()
var sentConstraints = [NSLayoutConstraint]()

...

final func changeCellMode(to mode: SNKMessage.Mode, didChangeMessageMode: (Bool) -> ()) {
    if let _previousMode = previousMessageMode, _previousMode == mode {
        didChangeMessageMode(false)
        messageBackground.setNeedsDisplay()
        return
    }
    
    didChangeMessageMode(true)
    if mode == .outgoing {
        NSLayoutConstraint.deactivate(receivedConstraints)
        NSLayoutConstraint.activate(sentConstraints)
    } else {
        NSLayoutConstraint.deactivate(sentConstraints)
        NSLayoutConstraint.activate(receivedConstraints)
    }
    
    messageBackground.messageMode = mode
    previousMessageMode = mode
    setNeedsLayout()
}

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