ios - UICollectionViewLayout 和 NavigationBar - y 位置错误

Question

我发现了这个不错的 UICollectionViewLayout ExpandingCollectionView问题是:一旦我向 ViewController 添加导航栏(带有搜索栏和缩放栏)， Collection View 就会滑到下面。

import Foundation
import UIKit

/* The heights are declared as constants outside of the class so they can be easily referenced elsewhere */
struct UltravisualLayoutConstants {
    struct Cell {
        /* The height of the non-featured cell */
        static let standardHeight: CGFloat = 100
        /* The height of the first visible cell */
        static let featuredHeight: CGFloat = 280
    }
}

class UltravisualLayout:UICollectionViewLayout{

    // MARK: Properties and Variables

    /* The amount the user needs to scroll before the featured cell changes */
    let dragOffset: CGFloat = 180.0

    var cache = [UICollectionViewLayoutAttributes]()

    /* Returns the item index of the currently featured cell */
    var featuredItemIndex: Int {
        get {
            /* Use max to make sure the featureItemIndex is never < 0 */
            return max(0, Int(collectionView!.contentOffset.y / dragOffset))
        }
    }

    /* Returns a value between 0 and 1 that represents how close the next cell is to becoming the featured cell */
    var nextItemPercentageOffset: CGFloat {
        get {
            return (collectionView!.contentOffset.y / dragOffset) - CGFloat(featuredItemIndex)
        }
    }

    /* Returns the width of the collection view */
    var width: CGFloat {
        get {
            return collectionView!.bounds.width
        }
    }

    /* Returns the height of the collection view */
    var height: CGFloat {
        get {
            return collectionView!.bounds.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 the content in the 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.zero
        var y: CGFloat = 0

        for item in 0..<numberOfItems {
            // 1
            let indexPath = IndexPath(item:item, section:0)
            let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)

            // 2
            attributes.zIndex = item
            var height = standardHeight

            // 3
            if indexPath.item == featuredItemIndex {
                // 4
                let yOffset = standardHeight * nextItemPercentageOffset
                y = collectionView!.contentOffset.y - yOffset
                height = featuredHeight
            } else if indexPath.item == (featuredItemIndex + 1) && indexPath.item != numberOfItems {
                // 5
                let maxY = y + standardHeight
                height = standardHeight + max((featuredHeight - standardHeight) * nextItemPercentageOffset, 0)
                y = maxY - height
            }

            // 6
            frame = CGRect(x: 0, y: y, width: width, height: height)
            attributes.frame = frame
            cache.append(attributes)
            y = frame.maxY
        }
    }

    /* Return all attributes in the 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 the layout is continuously invalidated as the user scrolls */
    override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        return true
    }

    override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint {
        let itemIndex = round(proposedContentOffset.y / dragOffset)
        let yOffset = itemIndex * dragOffset
        return CGPoint(x: 0, y: yOffset)
    }
}

谁能告诉我，我需要在哪里调整代码？我真的不知道，但我必须在明天之前实现此代码:O

非常感谢!

这是 UICollectionViewController:

import UIKit

private let reuseIdentifier = "Cell"

class InspirationsViewController: UICollectionViewController {

   let inspirations = Inspiration.allInspirations()


    override func viewDidLoad() {
        super.viewDidLoad()

        if let patternImage = UIImage(named: "Pattern") {
            view.backgroundColor = UIColor(patternImage: patternImage)
        }
        collectionView!.backgroundColor = UIColor.clear
        collectionView!.decelerationRate = UIScrollViewDecelerationRateFast

        let searchController = UISearchController(searchResultsController: nil)
        searchController.searchBar.scopeButtonTitles = ["All", "Chocolate", "Hard", "Other"]
        navigationItem.searchController = searchController
        navigationItem.hidesSearchBarWhenScrolling = true
        definesPresentationContext = true

        self.definesPresentationContext = true
    }

}

extension InspirationsViewController {

    override func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }

    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return inspirations.count
    }

    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "InspirationCell", for: indexPath) as! InspirationCell
        cell.inspiration = inspirations[indexPath.item]
        return cell
    }

    override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        let layout = collectionViewLayout as! UltravisualLayout
        let offset = layout.dragOffset * CGFloat(indexPath.item)
        if collectionView.contentOffset.y != offset {
            collectionView.setContentOffset(CGPoint(x: 0, y: offset), animated: true)
        }
    }
}

Answer 1

布局collectionView时，使用safe area guides :

NSLayoutConstraint.activate([
    collectionView.topAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.topAnchor),
    collectionView.leftAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.leftAnchor),
    collectionView.rightAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.rightAnchor),
    collectionView.bottomAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.bottomAnchor),
])

或者也许您可以使用UICollectionViewController(如果您没有使用它)，它应该隐式地处理它。