使用Swift 3在UICollectionView上自定义布局

import UIKit

class CustomLayout: UICollectionViewLayout {
    // 定义布局属性数组
    private var layoutAttributes: [UICollectionViewLayoutAttributes] = []
    
    override func prepare() {
        super.prepare()
        
        // 清空布局属性数组
        layoutAttributes.removeAll()
        
        // 计算每个单元格的位置和大小
        let itemCount = collectionView?.numberOfItems(inSection: 0) ?? 0
        for item in 0..<itemCount {
            let indexPath = IndexPath(item: item, section: 0)
            let attribute = UICollectionViewLayoutAttributes(forCellWith: indexPath)
            
            // 自定义单元格的布局属性，例如位置和大小
            // 这里只是简单地将每个单元格放置在网格中的不同位置
            let x = CGFloat(item % 3) * 100
            let y = CGFloat(item / 3) * 100
            attribute.frame = CGRect(x: x, y: y, width: 100, height: 100)
            
            // 将布局属性添加到数组中
            layoutAttributes.append(attribute)
        }
    }
    
    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        return layoutAttributes.filter { $0.frame.intersects(rect) }
    }
    
    override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        return layoutAttributes.first { $0.indexPath == indexPath }
    }
    
    override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        return true
    }
}

import UIKit

class ViewController: UIViewController, UICollectionViewDataSource {
    @IBOutlet weak var collectionView: UICollectionView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 设置自定义布局
        let customLayout = CustomLayout()
        collectionView.collectionViewLayout = customLayout
        
        // 注册单元格
        collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "Cell")
        
        // 设置数据源
        collectionView.dataSource = self
    }
    
    // 实现UICollectionViewDataSource协议方法
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 9
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath)
        cell.backgroundColor = UIColor.red
        return cell
    }
}