瀑布流

import UIKit

public protocol SPWaterflowLayoutDelegate: NSObjectProtocol {
    func waterflowLayout(view: SPWaterflowLayout, heightForItemAtIndex: IndexPath, itemWidth: CGFloat) -> CGFloat
}

public class SPWaterflowLayout: UICollectionViewFlowLayout {
    
    weak open var delegate: SPWaterflowLayoutDelegate?
    
    public var columnCount: NSInteger = 2
    public var columnMargin: CGFloat = 10
    public var rowMargin: CGFloat = 10
    public var edgeInsets: UIEdgeInsets = UIEdgeInsets(top: 10, left: 10, bottom: 10, right: 10)
    
    private var attrsArray = [UICollectionViewLayoutAttributes]()
    private var columnHeights = [CGFloat]()
    private var contentHeight: CGFloat = 0
}

extension SPWaterflowLayout {
    
    public override func prepare() {
        super.prepare()
        
        contentHeight = 0
        columnHeights.removeAll()
        
        for _ in 0..<columnCount {
            columnHeights.append(edgeInsets.top)
        }
        
        attrsArray.removeAll()
        guard let sections = collectionView?.numberOfSections else { return }
        for section in 0..<sections {
            guard let count = collectionView?.numberOfItems(inSection: section) else { return }
            for i in 0..<count {
                if let attrs = layoutAttributesForItem(at: IndexPath(item: i, section: section)) {
                    attrsArray.append(attrs)
                }
            }
        }
    }
    
    public override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        return attrsArray
    }
    
    public override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        
        let attrs = UICollectionViewLayoutAttributes(forCellWith: indexPath)
        guard let collectionViewWidth = collectionView?.frame.width else { return attrs }
        
        let width = (collectionViewWidth - edgeInsets.left - edgeInsets.right - (CGFloat(columnCount) - 1) * columnMargin) / CGFloat(columnCount)
        guard let height = delegate?.waterflowLayout(view: self, heightForItemAtIndex: indexPath, itemWidth: width) else { return attrs }
        
        var destColumn: NSInteger = 0
        var minColumnHeight: CGFloat = columnHeights[0]
        
        for i in 0..<columnCount {
            let columnHeight = columnHeights[i]
            if minColumnHeight > columnHeight {
                minColumnHeight = columnHeight
                destColumn = i
            }
        }
        
        let x = edgeInsets.left + CGFloat(destColumn) * (width + columnMargin)
        var y = minColumnHeight
        
        if y != edgeInsets.top {
            y += rowMargin
        }
        
        attrs.frame = CGRect(x: x, y: y, width: width, height: height)
        
        columnHeights[destColumn] = attrs.frame.maxY
        
        let columnHeight = columnHeights[destColumn]
        if contentHeight < columnHeight {
            contentHeight = columnHeight
        }
        
        return attrs
    }
    
    public override var collectionViewContentSize: CGSize {
        return CGSize(width: 0, height: contentHeight + edgeInsets.bottom)
    }
}

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标签

import UIKit

public protocol SPTagsListLayoutDelegate: NSObjectProtocol {
    func tagsListLayout(view: SPTagsListLayout, widthForItemAtIndex: IndexPath, itemHeight: CGFloat) -> CGFloat
    func tagsListLayout(view: SPTagsListLayout, maxHeight: CGFloat)
}

public class SPTagsListLayout: UICollectionViewFlowLayout {
    
    weak open var delegate: SPTagsListLayoutDelegate?
    
    public var itemHeight: CGFloat = 25
    public var columnMargin: CGFloat = 10
    public var rowMargin: CGFloat = 10
    public var edgeInsets: UIEdgeInsets = UIEdgeInsets(top: 10, left: 10, bottom: 10, right: 10)
    
    private var attrsArray = [UICollectionViewLayoutAttributes]() 
    private var preAttrs = [String : UICollectionViewLayoutAttributes]()
    private var maxY: CGFloat = 0
}

extension SPTagsListLayout {
    
    public override func prepare() {
        super.prepare()
        
        attrsArray.removeAll()
        guard let sections = collectionView?.numberOfSections else { return }
        for section in 0..<sections {
            guard let count = collectionView?.numberOfItems(inSection: section) else { return }
            for i in 0..<count {
                if let attrs = layoutAttributesForItem(at: IndexPath(item: i, section: section)) {
                    attrsArray.append(attrs)
                }
            }
        }
    }
    
    public override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        return attrsArray
    }
    
    public override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        
        let attrs = UICollectionViewLayoutAttributes(forCellWith: indexPath)
        guard let collectionViewWidth = collectionView?.frame.width,
              var currentWidth = delegate?.tagsListLayout(view: self, widthForItemAtIndex: indexPath, itemHeight: itemHeight) else { return attrs }
        currentWidth = min(currentWidth, collectionViewWidth - edgeInsets.left - edgeInsets.right)
        
        let key = "preAttrs_key_\(indexPath.section)_\(indexPath.row)"
        var x: CGFloat = edgeInsets.left
        var y: CGFloat = edgeInsets.top
        
        if indexPath.row - 1 >= 0 {
            let preKey = "preAttrs_key_\(indexPath.section)_\(indexPath.row - 1)"
            if let preAttr = preAttrs[preKey] {
                y = preAttr.frame.origin.y
                x = (preAttr.frame.maxX + columnMargin)
            }
        }
        
        if x + currentWidth > collectionViewWidth - edgeInsets.right {
            x = edgeInsets.left
            y += (rowMargin + itemHeight)
        }
        
        let attr = UICollectionViewLayoutAttributes(forCellWith: indexPath)
        attr.frame = CGRect(x: x, y: y, width: currentWidth, height: itemHeight)
        
        preAttrs[key] = attr
        maxY = attr.frame.maxY
        
        return attr
    }
    
    public override var collectionViewContentSize: CGSize {
        delegate?.tagsListLayout(view: self, maxHeight: maxY + edgeInsets.bottom)
        return CGSize(width: 0, height: maxY + edgeInsets.bottom)
    }
}

标签使用 ：

代理 func tagsListLayout(view: SPTagsListLayout, maxHeight: CGFloat) 返回的 maxHeight 不要超过 UICollectionView 的高度

import UIKit

class ViewController: UIViewController, SPTagsListLayoutDelegate, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
    
    private lazy var contentView: UIView = {
        let view = UIView(frame: CGRect(x: 20, y: 100, width: UIScreen.main.bounds.width - 40, height: 0))
        view.clipsToBounds = true
        return view
    }()
    
    private lazy var collectionView: UICollectionView = {
        
        let layout = SPTagsListLayout()
        layout.delegate = self
        
        let view = UICollectionView(frame: CGRect(x: 0, y: 0, width: UIScreen.main.bounds.width - 40, height: UIScreen.main.bounds.height), collectionViewLayout: layout)
        view.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "UICollectionViewCellID")
        view.delegate = self
        view.dataSource = self
        view.backgroundColor = .white
        
        return view
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        view.backgroundColor = UIColor.lightGray
        
        view.addSubview(contentView)
        contentView.addSubview(collectionView)
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 50
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "UICollectionViewCellID", for: indexPath)
        cell.backgroundColor = UIColor(red: CGFloat(arc4random() % 256) / 255.0, green: CGFloat(arc4random() % 256) / 255.0, blue: CGFloat(arc4random() % 256) / 255.0, alpha: 1.0)
        return cell
    }
    
    func tagsListLayout(view: SPTagsListLayout, widthForItemAtIndex: IndexPath, itemHeight: CGFloat) -> CGFloat {
        return CGFloat(arc4random_uniform(100) + 10)
    }
    
    func tagsListLayout(view: SPTagsListLayout, maxHeight: CGFloat) {
        contentView.frame.size.height = maxHeight
    }
}

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