问将自定义布局类连接到代码中的集合视图

EN

import UIKit
import Firebase
class UserProfileController: UICollectionViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        collectionView?.backgroundColor = .white
        //fetchUser()
        collectionView?.dataSource = self
        collectionView?.delegate = self
        collectionView?.register(TestCell.self, forCellWithReuseIdentifier: mainCellId)    
    }


    fileprivate let mainCellId = "mainCellId"
    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: mainCellId, for: indexPath) as! TestCell

        return cell
    }

    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 15
    }
    override func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }
}

import UIKit

struct UltraVisualLayoutConstants {
    struct Cell {
        static let standardHeight: CGFloat = 100
        static let featuredHeight: CGFloat = 280
//        static let standardWidth: CGFloat = 100
//        static let featuredWidth: CGFloat = 280
    }
}

class UltraVisualLayout: UICollectionViewLayout {
    //  amount which users need to scroll before featured cell changes\
    let dragOffset: CGFloat = 180.0
    var cache = [UICollectionViewLayoutAttributes]()
    //return item index of current featured cell
    var featuredItemIndex: Int {
        get {
            //use max to ensure that featureditemindex never be < 0
            return max(0 , Int(collectionView!.contentOffset.y / dragOffset))
        }
    }

    // returns value between 0 and 1 to represent how close the next cell becomes the featured cell
    var nextItemPercentegeOffset: CGFloat {
        get {
            return (collectionView!.contentOffset.y / dragOffset) - CGFloat(featuredItemIndex)
        }
    }    
    // return the width of collection view
    var width: CGFloat {
        get {

            guard let width = collectionView?.bounds.width else {return 0}
            return width
        }
    }
    // return the height of collection view
    var height: CGFloat {
        get {
            guard let height = collectionView?.bounds.height else {return 0}
            return height
        }
    }
    //returns the number of items in the collection view
    var numberOfItems: Int {
        get {
            return collectionView!.numberOfItems(inSection: 0)
        }
    }

    // MARK: UICollectionViewLayout
    // return the size of all content in collection view
     override var collectionViewContentSize: CGSize {
   let contentHeight = (CGFloat(numberOfItems) * dragOffset) + (height - dragOffset)
    return CGSize(width: width, height: contentHeight)
}
    override func prepare() {
        cache.removeAll(keepingCapacity: false)

        let standardHeight = UltraVisualLayoutConstants.Cell.standardHeight
        let featuredHeight = UltraVisualLayoutConstants.Cell.featuredHeight
        var frame = CGRect(x: 0, y: 0, width: 0, height: 0)
        var y: CGFloat = 0
        for item in 0..<numberOfItems {
            let indexPath = NSIndexPath(item: item, section: 0)
            let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath as IndexPath)
            attributes.zIndex = item
            var height = standardHeight
            if indexPath.item == featuredItemIndex {
                let yOffset = standardHeight * nextItemPercentegeOffset
                y = collectionView!.contentOffset.y - yOffset
                height = featuredHeight
            } else if indexPath.item == (featuredItemIndex + 1) && indexPath.item != numberOfItems {
                let maxY = y + standardHeight
                height = standardHeight + max((featuredHeight - standardHeight) * nextItemPercentegeOffset, 0)
                y = maxY - height
            }
         frame = CGRect(x: 0, y: y, width: width, height: height)
            attributes.frame = frame
            cache.append(attributes)
            y = frame.maxY
        }

    }

    // return all attributes in cache whose frame intersects with the rect passed to the method
    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        var layoutAttributes = [UICollectionViewLayoutAttributes]()
        for attributes in cache {
            if attributes.frame.intersects(rect) {
                layoutAttributes.append(attributes)
            }
        }
        return layoutAttributes
    }

    // return true so that layout is continuously invalidated as the user scrolls
    override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        return true 
    }