表格单元格重用 UIKit 上的限制重置

如何解决表格单元格重用 UIKit 上的限制重置

我正在制作一个聊天应用程序并试图找出表格单元格的重用机制。根据传入/传出的消息，我无法将聊天气泡左右对齐。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）在单元格被重用时重置，导致气泡对齐到前导侧。我该怎么做才能成功更新约束而不遇到此类问题？

解决方法

我发现将 .isActive 设置为 false 实际上消除了约束（将属性设置为 nil）。如 this answer 中所述，我尝试使约束类属性不是 weak 并且一切正常！

现在代码看起来像这样：

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
        }
    }
    
}