我尝试使用estimatedItemSize，但在插入和删除单元格时，如果estimatedItemSize不完全等于单元格的高度，则有一堆错误。我停止设置estimatedItemSize，并通过使用原型单元格实现动态单元格。这是如何做到的:

创建这个协议:

protocol SizeableCollectionViewCell {
    func fittedSize(forConstrainedSize size: CGSize)->CGSize
}

在你的自定义UICollectionViewCell中实现这个协议:

class YourCustomCollectionViewCell: UICollectionViewCell, SizeableCollectionViewCell {

    @IBOutlet private var mTitle: UILabel!
    @IBOutlet private var mDescription: UILabel!
    @IBOutlet private var mContentView: UIView!
    @IBOutlet private var mTitleTopConstraint: NSLayoutConstraint!
    @IBOutlet private var mDesciptionBottomConstraint: NSLayoutConstraint!

    func fittedSize(forConstrainedSize size: CGSize)->CGSize {

        let fittedSize: CGSize!

        //if height is greatest value, then it's dynamic, so it must be calculated
        if size.height == CGFLoat.greatestFiniteMagnitude {

            var height: CGFloat = 0

            /*now here's where you want to add all the heights up of your views.
              apple provides a method called sizeThatFits(size:), but it's not 
              implemented by default; except for some concrete subclasses such 
              as UILabel, UIButton, etc. search to see if the classes you use implement 
              it. here's how it would be used:
            */
            height += mTitle.sizeThatFits(size).height
            height += mDescription.sizeThatFits(size).height
            height += mCustomView.sizeThatFits(size).height    //you'll have to implement this in your custom view

            //anything that takes up height in the cell has to be included, including top/bottom margin constraints
            height += mTitleTopConstraint.constant
            height += mDescriptionBottomConstraint.constant

            fittedSize = CGSize(width: size.width, height: height)
        }
        //else width is greatest value, if not, you did something wrong
        else {
            //do the same thing that's done for height but with width, remember to include leading/trailing margins in calculations
        }

        return fittedSize
    }
}

现在让你的控制器符合UICollectionViewDelegateFlowLayout，在它里面，有这个字段:

class YourViewController: UIViewController, UICollectionViewDelegateFlowLayout {
    private var mCustomCellPrototype = UINib(nibName: <name of the nib file for your custom collectionviewcell>, bundle: nil).instantiate(withOwner: nil, options: nil).first as! SizeableCollectionViewCell
}

它将被用作一个原型单元格来绑定数据，然后确定该数据如何影响您想要动态的维度

最后，必须实现uicollectionviewdelegatflowlayout的collectionView(:layout:sizeForItemAt:):

class YourViewController: UIViewController, UICollectionViewDelegateFlowLayout, UICollectionViewDataSource {

    private var mDataSource: [CustomModel]

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath)->CGSize {

        //bind the prototype cell with the data that corresponds to this index path
        mCustomCellPrototype.bind(model: mDataSource[indexPath.row])    //this is the same method you would use to reconfigure the cells that you dequeue in collectionView(:cellForItemAt:). i'm calling it bind

        //define the dimension you want constrained
        let width = UIScreen.main.bounds.size.width - 20    //the width you want your cells to be
        let height = CGFloat.greatestFiniteMagnitude    //height has the greatest finite magnitude, so in this code, that means it will be dynamic
        let constrainedSize = CGSize(width: width, height: height)

        //determine the size the cell will be given this data and return it
        return mCustomCellPrototype.fittedSize(forConstrainedSize: constrainedSize)
    }
}

就是这样。在collectionView(:layout:sizeForItemAt:)中返回单元格的大小，以这种方式防止我不得不使用estimatedItemSize，并且插入和删除单元格工作得很好。

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:.

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.

---

如果你实现uicollectionviewdelegatflowlayout方法:

- (CGSize)collectionView:(UICollectionView*)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath*)indexPath

当你调用collectionview performBatchUpdates:completion:时，size height将使用sizeForItemAtIndexPath代替 preferredLayoutAttributesFittingAttributes。

performBatchUpdates:completion的呈现过程将通过preferredLayoutAttributesFittingAttributes方法，但它会忽略您的更改。

编辑11/19/19:对于iOS 13，只使用UICollectionViewCompositionalLayout估计高度。不要浪费时间处理这个坏的API。

在与此斗争了一段时间后，我注意到，如果你不禁用滚动，调整大小对UITextViews不起作用:

let textView = UITextView()
textView.scrollEnabled = false

在Swift 5中，它适用于我。

UICollectionViewFlowLayout:

estimatedItemSize = UICollectionViewFlowLayout.automaticSize

UICollectionViewCell:

(ps:我用的是SnapKit)

class Cell: UICollectionViewCell {
    let customizedContentView = UIView()
    ...
    func layoutAction() {
        contentView.translatesAutoresizingMaskIntoConstraints = false
        contentView.addSubview(customizedContentView)
        customizedContentView.snp.makeConstraints { make in
            make.edges.equalToSuperview()
        }
    }
}

然后你只需要展开customizedContentView。