解决方案包括3个简单步骤:

启用动态单元格大小

flowLayout.estimatedItemSize = UICollectionViewFlowLayout.automaticSize

设置来自collectionView(:cellForItemAt:)的containerview . widthachor .constraint来限制contentView的宽度为collectionView的宽度。

class ViewController: UIViewController, UICollectionViewDataSource {
    ...

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cellId", for: indexPath) as! MultiLineCell
        cell.textView.text = dummyTextMessages[indexPath.row]
        cell.maxWidth = collectionView.frame.width
        return cell
    }

    ...
}

class MultiLineCell: UICollectionViewCell{
    ....

    var maxWidth: CGFloat? {
        didSet {
            guard let maxWidth = maxWidth else {
                return
            }
            containerViewWidthAnchor.constant = maxWidth
            containerViewWidthAnchor.isActive = true
        }
    }

    ....
}

因为你想要启用UITextView的自调整大小，它有一个额外的步骤来;

3.计算和设置高度tanchor。常量的UITextView。

当contentView的宽度被设置时，我们会在didSet的maxWidth中调整UITextView的高度。

UICollectionViewCell Inside job:

var maxWidth: CGFloat? {
    didSet {
        guard let maxWidth = maxWidth else {
            return
        }
        containerViewWidthAnchor.constant = maxWidth
        containerViewWidthAnchor.isActive = true
        
        let sizeToFitIn = CGSize(width: maxWidth, height: CGFloat(MAXFLOAT))
        let newSize = self.textView.sizeThatFits(sizeToFitIn)
        self.textViewHeightContraint.constant = newSize.height
    }
}

这些步骤会让你得到想要的结果。

完整的可运行的要旨

参考:Vadim Bulavin博客文章-集合视图单元格自我调整:一步一步的教程

截图:

这个答案在iOS 14中已经过时了，因为添加了复合布局。请考虑更新新的API

Swift 5更新

preferredLayoutAttributesFittingAttributes重命名为preferredLayoutAttributesFitting并使用自动调整大小

---

Swift 4更新

systemLayoutSizeFittingSize重命名为systemlayoutsizefiting

---

iOS 9更新

在看到我的GitHub解决方案在iOS 9下崩溃后，我终于有时间全面调查这个问题。我现在已经更新了repo，以包括几个不同配置的自调整单元格的示例。我的结论是，自我调整单元格在理论上很好，但在实践中很混乱。在处理自调整单元格时要注意一点。

博士TL;

看看我的GitHub项目

---

自我调整单元格只支持流布局，所以要确保这是你正在使用的。

要使自调整大小的单元格工作，需要设置两件事。

# 1。在UICollectionViewFlowLayout上设置estimatedItemSize

一旦您设置了estimatedItemSize属性，流布局将在本质上成为动态的。

self.flowLayout.estimatedItemSize = UICollectionViewFlowLayout.automaticSize

# 2。在单元格子类上添加大小调整支持

这有两种口味;自动布局或自定义覆盖preferredLayoutAttributesFittingAttributes。

使用自动布局创建和配置单元格

我不会详细介绍这一点，因为有一篇关于为单元配置约束的精彩SO帖子。只是要小心，Xcode 6打破了一大堆东西与iOS 7，所以，如果你支持iOS 7，你将需要做的事情，如确保autoresizingMask设置在单元格的contentView和contentView的边界设置为单元格的边界时加载单元格(即awakeFromNib)。

你需要注意的是你的单元格需要比表格视图单元格更严格的约束。例如，如果你想要你的宽度是动态的，那么你的单元格需要一个高度约束。同样地，如果你想要高度是动态的，那么你需要一个宽度约束你的单元格。

在自定义单元格中实现preferredLayoutAttributesFittingAttributes

当这个函数被调用时，你的视图已经配置了内容(即cellForItem已经被调用)。假设你已经适当地设置了约束，你可以有一个这样的实现:

//forces the system to do one layout pass
var isHeightCalculated: Bool = false

override func preferredLayoutAttributesFitting(_ layoutAttributes: UICollectionViewLayoutAttributes) -> UICollectionViewLayoutAttributes {
    //Exhibit A - We need to cache our calculation to prevent a crash.
    if !isHeightCalculated {
        setNeedsLayout()
        layoutIfNeeded()
        let size = contentView.systemLayoutSizeFitting(layoutAttributes.size)
        var newFrame = layoutAttributes.frame
        newFrame.size.width = CGFloat(ceilf(Float(size.width)))
        layoutAttributes.frame = newFrame
        isHeightCalculated = true
    }
    return layoutAttributes
}

NOTE On iOS 9 the behaviour changed a bit that could cause crashes on your implementation if you are not careful (See more here). When you implement preferredLayoutAttributesFittingAttributes you need to ensure that you only change the frame of your layout attributes once. If you don't do this the layout will call your implementation indefinitely and eventually crash. One solution is to cache the calculated size in your cell and invalidate this anytime you reuse the cell or change its content as I have done with the isHeightCalculated property.

体验你的布局

此时，您的collectionView中应该有“功能正常”的动态单元格。我还没有发现开箱即用的解决方案充分在我的测试，所以请随意评论，如果你有。在我看来，UITableView仍然赢得了动态大小的战斗。

##Caveats Be very mindful that if you are using prototype cells to calculate the estimatedItemSize - this will break if your XIB uses size classes. The reason for this is that when you load your cell from a XIB its size class will be configured with Undefined. This will only be broken on iOS 8 and up since on iOS 7 the size class will be loaded based on the device (iPad = Regular-Any, iPhone = Compact-Any). You can either set the estimatedItemSize without loading the XIB, or you can load the cell from the XIB, add it to the collectionView (this will set the traitCollection), perform the layout, and then remove it from the superview. Alternatively you could also make your cell override the traitCollection getter and return the appropriate traits. It's up to you.

---

在iOS 10+中，这是一个非常简单的2步过程。

Ensure that all your cell contents are placed within a single UIView (or inside a descendant of UIView like UIStackView which simplifies autolayout a lot). Just like with dynamically resizing UITableViewCells, the whole view hierarchy needs to have constraints configured, from the outermost container to the innermost view. That includes constraints between the UICollectionViewCell and the immediate childview Instruct the flowlayout of your UICollectionView to size automatically yourFlowLayout.estimatedItemSize = UICollectionViewFlowLayout.automaticSize

更新更多信息:

If you use flowLayout.estimatedItemSize, suggest use iOS8.3 later version. Before iOS8.3, it will crash [super layoutAttributesForElementsInRect:rect];. The error message is *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSArrayM insertObject:atIndex:]: object cannot be nil' Second, in iOS8.x version, flowLayout.estimatedItemSize will cause different section inset setting did not work. i.e. function: (UIEdgeInsets)collectionView:layout:insetForSectionAtIndex:.

内容查看主播奥秘:

在一个奇怪的例子中

    contentView.translatesAutoresizingMaskIntoConstraints = false

不会起作用。在contentView中添加了四个显式的锚，它工作了。

class AnnoyingCell: UICollectionViewCell {
    
    @IBOutlet var word: UILabel!
    
    override init(frame: CGRect) {
        super.init(frame: frame); common() }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder); common() }
    
    private func common() {
        contentView.translatesAutoresizingMaskIntoConstraints = false
        
        NSLayoutConstraint.activate([
            contentView.leftAnchor.constraint(equalTo: leftAnchor),
            contentView.rightAnchor.constraint(equalTo: rightAnchor),
            contentView.topAnchor.constraint(equalTo: topAnchor),
            contentView.bottomAnchor.constraint(equalTo: bottomAnchor)
        ])
    }
}

像往常一样

    estimatedItemSize = UICollectionViewFlowLayout.automaticSize

在你的布局:UICollectionViewFlowLayout

谁知道呢?也许能帮到别人。

信贷

https://www.vadimbulavin.com/collection-view-cells-self-sizing/

无意中发现了这个技巧——在其他1000篇文章中从未见过。

在viewDidLoad()上添加flowLayout override func viewDidLoad() { super.viewDidLoad () if let flowLayout = infoCollection。collectionViewLayout一样吗?UICollectionViewFlowLayout { estimateditemsize = CGSize(宽度:1，高度:1) ｝ ｝ 此外，设置一个UIView为单元的mainContainer，并在其中添加所有必需的视图。 参考这个很棒的，令人兴奋的教程，以获得进一步的参考: 在iOS 9和10中使用自动布局自动调整单元格的UICollectionView