swift - 将 IGListKit 用于带分页的水平列表

Question

我正在构建一个严重依赖 Collection View 的应用程序，因此我决定使用 IGListKit。这是我必须做的:

这是我所拥有的:

...而且它没有朝任何方向移动!

这是我的代码:

import UIKit
import IGListKit

class MatchCollectionViewCell: UICollectionViewCell {
    var helloWorld = "Hello World"
}

class LabelSectionController: ListSectionController {
    override func sizeForItem(at index: Int) -> CGSize {
        return CGSize(width: collectionContext!.containerSize.width, height: 55)
    }

    override func cellForItem(at index: Int) -> UICollectionViewCell {
        return collectionContext!.dequeueReusableCell(of: MatchCollectionViewCell.self, for: self, at: index)
    }
}

class MatchViewController: UIViewController {

    // MARK: - Outlets
    @IBOutlet weak var matchCollectionView: UICollectionView!


    // MARK: - Variables
    let layout = UICollectionViewFlowLayout()
    lazy var adapter: ListAdapter = {
        return ListAdapter(updater: ListAdapterUpdater(), viewController: self, workingRangeSize: 0)
    }()
    var users: [User] = []

    // MARK: - Lifecycle
    override func viewDidLoad() {
        super.viewDidLoad()
        matchCollectionView.dataSource = self
        matchCollectionView.delegate = self
        matchCollectionView.collectionViewLayout = CenterCellCollectionViewFlowLayout()
        matchCollectionView.isPagingEnabled = true
        layout.minimumLineSpacing = 8
        layout.scrollDirection = .horizontal

        for i in 1...10 {
            let newMatchingPreferences = MatchingPreferences(preferedAge: (23, 33))
            let newUser = User(id: i, name: "Some Name \(i)", email: "some_name@gmail.com", age: 27, location: "New York", isOnboarded: true, isPremium: true, matchingPreferences: newMatchingPreferences)
            users.append(newUser)
        }
    }

    // MARK: - Actions

    // MARK: - Methods
}

extension MatchViewController: ListAdapterDataSource {
    func objects(for listAdapter: ListAdapter) -> [ListDiffable] {
        return self.users
    }

    func listAdapter(_ listAdapter: ListAdapter, sectionControllerFor object: Any) -> ListSectionController {
        return LabelSectionController()
    }

    func emptyView(for listAdapter: ListAdapter) -> UIView? {
        let view = UIView()
        view.backgroundColor = .lightGray
        return view
    }
}

extension MatchViewController: UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout {
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 10
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = matchCollectionView.dequeueReusableCell(withReuseIdentifier: "MatchCell", for: indexPath) as! MatchCollectionViewCell
        print(cell.helloWorld)
        return cell
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: view.bounds.width - 32, height: view.bounds.height - 40)
    }


    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
        return .zero
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
        return 0
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
        return 0
    }
}

class CenterCellCollectionViewFlowLayout: UICollectionViewFlowLayout {
    var mostRecentOffset: CGPoint = CGPoint.zero

    override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint {

        if velocity.x == 0 {
            return self.mostRecentOffset
        }

        guard let cv = self.collectionView,
            let attributesForVisibleCells = self.layoutAttributesForElements(in: cv.bounds) else {
                // Fallback
                self.mostRecentOffset = super.targetContentOffset(forProposedContentOffset: proposedContentOffset)
                return self.mostRecentOffset
        }

        let halfWidth = cv.bounds.size.width * 0.5

        var candidateAttributes: UICollectionViewLayoutAttributes?
        for attributes in attributesForVisibleCells {

            // Skip comparison with non-cell items (headers and footers)
            if attributes.representedElementCategory != UICollectionElementCategory.cell {
                continue
            }

            if (attributes.center.x == 0) || (attributes.center.x > (cv.contentOffset.x + halfWidth) && velocity.x < 0) {
                continue
            }

            candidateAttributes = attributes
        }

        // Beautification step , I don't know why it works!
        if proposedContentOffset.x == -(cv.contentInset.left) {
            return proposedContentOffset
        }

        guard let attributes = candidateAttributes else {
            return mostRecentOffset
        }

        self.mostRecentOffset = CGPoint(x: floor(attributes.center.x - halfWidth), y: proposedContentOffset.y)

        return self.mostRecentOffset
    }
}

基本上，我知道如何制作粗略的 Collection View ，但分页和居中对我来说有点难。我觉得我很接近，但显然缺少一些东西。我希望有人能指出我正确的方向!谢谢。

Answer 1

    extension ViewController: UIScrollViewDelegate {
    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        if scrollView == self.collectionView {
            var currentCellOffset = self.collectionView.contentOffset
            currentCellOffset.x += self.collectionView.frame.width / 2
            if let indexPath = self.collectionView.indexPathForItem(at: currentCellOffset) {
                self.collectionView.scrollToItem(at: indexPath, at: .centeredHorizontally, animated: true)
            }
        }
    }
}

确保设置

adapter.scrollDelegate = self

和

collectionView.decelerationRate = UIScrollViewDecelerationRateFast

(更多原生 iOS 的感觉)

这对我有用，希望对其他人有帮助!