在 table 单元重用 UIKit 时重置约束

Question

我正在制作一个聊天应用程序并试图找出 table 单元格重用机制。根据 incoming/ougoing 消息，我无法左右对齐聊天气泡。我现在拥有的是：

class ConversationTableViewCell: UITableViewCell {
    @IBOutlet weak var messageTextLabel: UILabel?
    @IBOutlet weak var messageView: UIView?
    @IBOutlet weak var trailingPaddingConstraint: NSLayoutConstraint?
    @IBOutlet weak var leadingPaddingConstraint: NSLayoutConstraint?
    
    func configure(with data: ConversationViewController.ConversationDataModel.Message) {
        
        messageView?.layer.cornerRadius = 12
        messageTextLabel?.text = data.text
        
        switch data.messageType {
        case .incoming:
            trailingPaddingConstraint?.isActive = false
            leadingPaddingConstraint?.isActive = true
            messageView?.backgroundColor = UIColor(named: "IncomingMessage") ?? .gray
        case .outgoing:
            trailingPaddingConstraint?.isActive = true
            leadingPaddingConstraint?.isActive = false
            messageView?.backgroundColor = UIColor(named: "OutgoingMessage") ?? .green
        }
    }
}

如您所见，我正在根据消息类型启用或禁用所需的约束，但似乎这些约束（并且只有它们）在重复使用单元格时会重置，从而导致气泡与前导面对齐.我该怎么做才能成功更新约束而不是运行到这样的问题？

Answer 1

我发现将 .isActive 设置为 false 实际上会删除约束（将属性设置为 nil）。正如 this answer 中所述，我试图使约束 class 属性不是 weak 并且一切正常！

现在代码如下所示：

class ConversationTableViewCell: UITableViewCell {
    @IBOutlet weak var messageTextLabel: UILabel?
    @IBOutlet weak var messageView: UIView?
    @IBOutlet var trailingPaddingConstraint: NSLayoutConstraint? //not weak
    @IBOutlet var leadingPaddingConstraint: NSLayoutConstraint? //not weak
    
    func configure(with data: ConversationViewController.ConversationDataModel.Message) {
        messageView?.layer.cornerRadius = 12
        messageTextLabel?.text = data.text
        
        switch data.messageType {
        case .incoming:
            trailingPaddingConstraint?.isActive = false
            leadingPaddingConstraint?.isActive = true
            messageView?.backgroundColor = UIColor(named: "IncomingMessage") ?? .gray
        case .outgoing:
            trailingPaddingConstraint?.isActive = true
            leadingPaddingConstraint?.isActive = false
            messageView?.backgroundColor = UIColor(named: "OutgoingMessage") ?? .green
        }
    }
    
}

在 table 单元重用 UIKit 时重置约束

Contraints reset on table cell reuse UIKit

swift

uitableview

uikit

cell