swift - 我的 "Messaging app"代码中的约束问题

Question

我正在尝试制作一个应用程序。它有点像消息传递应用程序，所以我有发件人和收件人。我有一个 collectionView 作为我的主 Controller ，我有一个“ChatMessageCell”类，它是“UICollectionViewCell”类型，还有一个 NSObject 类型的类:“Message”。问题是，当我在我的代码中实现所有这些时，我遇到了很多约束问题(特别是当我尝试发送图像消息时)。

当我第一次发送一条消息像蓝色气泡，然后我发送另一条消息像灰色气泡时，问题就出现了。它向我显示这样的错误:

(此错误示例是当我发送一条蓝色消息(没有错误)然后我发送另一条灰色消息(出现错误))

[LayoutConstraints] Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. 
    Try this: 
        (1) look at each constraint and try to figure out which you don't expect; 
        (2) find the code that added the unwanted constraint or constraints and fix it. 
(
    "<NSLayoutConstraint:0x600000289790 UIView:0x7fbeead23880.width == 136.117   (active)>",
    "<NSLayoutConstraint:0x6000002896a0 UIView:0x7fbeead23880.right == practica_say_whaat.ChatMessageCell:0x7fbeead43770.right - 8   (active)>",
    "<NSLayoutConstraint:0x6000002892e0 H:|-(8)-[UIView:0x7fbeead23880](LTR)   (active, names: '|':practica_say_whaat.ChatMessageCell:0x7fbeead43770 )>",
    "<NSLayoutConstraint:0x60000028b540 'UIView-Encapsulated-Layout-Width' practica_say_whaat.ChatMessageCell:0x7fbeead43770.width == 375   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x600000289790 UIView:0x7fbeead23880.width == 136.117   (active)>

这些是导致错误的约束...聊天消息单元格:

var bubbleWidthAnchor: NSLayoutConstraint?
var bubbleViewRightAnchor: NSLayoutConstraint?
var bubbleViewLeftAnchor: NSLayoutConstraint?

override init(frame: CGRect) {
    super.init(frame: frame)

    addSubview(bubbleView)
    addSubview(textView)


    //This is the bubble of the message (here is an error)
    bubbleViewRightAnchor = bubbleView.rightAnchor.constraint(equalTo: self.rightAnchor, constant: -8)
    bubbleView.topAnchor.constraint(equalTo: self.topAnchor).isActive = true
    bubbleWidthAnchor = bubbleView.widthAnchor.constraint(equalToConstant: 200)
    bubbleWidthAnchor?.isActive = true
    bubbleView.heightAnchor.constraint(equalTo: self.heightAnchor).isActive = true

    bubbleViewLeftAnchor = bubbleView.leftAnchor.constraint(equalTo: self.leftAnchor, constant: 8)

主视图 Controller :

var messages = [Message]()

override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cellId", for: indexPath) as! ChatMessageCell

    let message = messages[indexPath.item]
    cell.textView.text = message.text

    setupCell(cell, message: message)

    if let text = message.text {
        //a text message
        cell.bubbleWidthAnchor?.constant = estimateFrameForText(text).width + 32
        cell.textView.isHidden = false
    } else if message.text == nil {
        //fall in here if its an image message
        cell.bubbleWidthAnchor?.constant = 200
        cell.textView.isHidden = true
    }


    return cell
}

//In this function, i think is the other error connected to the other one)
fileprivate func setupCell(_ cell: ChatMessageCell, message: Message) {

    if message.id == 1 {
        //outgoing blue
        cell.bubbleView.backgroundColor = ChatMessageCell.blueColor
        cell.textView.textColor = UIColor.white

        cell.bubbleViewRightAnchor?.isActive = true
        cell.bubbleViewLeftAnchor?.isActive = false
        cell.messageImageView.isHidden = true

    } else if message.id == 2 {
        //incoming gray
        cell.bubbleView.backgroundColor = UIColor(red: 240/255, green: 240/255, blue: 240/255, alpha: 1.0)
        cell.textView.textColor = UIColor.black

        cell.bubbleViewRightAnchor?.isActive = false
        cell.bubbleViewLeftAnchor?.isActive = true
        cell.messageImageView.isHidden = true
    }

    else if message.id == 3 {
        cell.messageImageView.image = imagenSeleccionada
        cell.messageImageView.isHidden = false
        cell.bubbleView.backgroundColor = UIColor.clear
    }
}

Answer 1

该错误意味着一个布局约束使另一个布局约束无法实现。唯一真正的解决方案是检查约束并找出哪些约束存在冲突以及原因。

附带说明一下，如果您只关心最终结果而不关心手段，那么我强烈建议您查看 JSQMessagesViewController .这是一个开源项目，可以避免尝试手动执行此操作的麻烦。