UICollectionViewCell 自动大小的两种常用方式

方法一：自动计算

override func viewDidLoad() {
   super.viewDidLoad()

   if let flowLayout = collectionView?.collectionViewLayout as? UICollectionViewFlowLayout {
      flowLayout.estimatedItemSize = UICollectionViewFlowLayout.automaticSize
    }
}

class YourCustomCollectionViewCell: UICollectionViewCell {
    override func preferredLayoutAttributesFitting(_ layoutAttributes: UICollectionViewLayoutAttributes) -> UICollectionViewLayoutAttributes {
        layoutAttributes.size = self.intrinsicContentSize
        return layoutAttributes 
    }

    override var intrinsicContentSize: CGSize {
        return self.someView.viewSize()
    }

    // ......

}

方法二：手动计算

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

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
    }
}

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

    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)
    }
}

参考

iOS自定义View 控件自动计算size能力https://blog.csdn.net/qq_14920635/article/details/115318381