为什么当我将滚动方向从垂直更改为水平时，集合视图会崩溃？

Question

我有一个集合视图，显示我传递给它的任何数据对象的一组视频。当您按下内容视图中的其中一个视频时，会出现一个新视图 (DetailViewController)，并且视频会以更详细的视图显示。在那个 DetailViewController 中有一个后退按钮，它关闭视图并让你回到带有集合视图的主页 - 这是崩溃发生的时候，当我从那个 'DetailViewController' 回到主视图控制器时。

当集合视图的 'scroll direction' 设置为垂直时一切正常，但是当我将它设置为水平时（这是我想要的），它会像上面解释的那样崩溃。

崩溃是：

Unexpectedly found nil while unwrapping an Optional value

来源是：

private func findCurrentCell(path: IndexPath) -> UICollectionViewCell {
    return playerCollect.cellForItem(at: path)!
}

我猜 path 或 IndexPath 在用户滚动时没有得到更新，所以索引没有得到更新？

有什么想法吗？如果需要我可以提供视频或一些额外的代码。

编辑（额外代码）：

import UIKit
import AVFoundation
import MMPlayerView

class ViewController: UIViewController {
    var offsetObservation: NSKeyValueObservation?
    lazy var mmPlayerLayer: MMPlayerLayer = {
    let l = MMPlayerLayer()        
    l.cacheType = .memory(count: 5)
    l.coverFitType = .fitToPlayerView
    l.videoGravity = AVLayerVideoGravity.resizeAspect
    l.replace(cover: CoverA.instantiateFromNib())
    l.repeatWhenEnd = true
    return l
}()

@IBOutlet weak var playerCollect: UICollectionView!
override func viewDidLoad() {
    super.viewDidLoad()
    // remove previous download fails file
    MMPlayerDownloader.cleanTmpFile()
    self.navigationController?.mmPlayerTransition.push.pass(setting: { (_) in

    })
    offsetObservation = playerCollect.observe(\.contentOffset, options: [.new]) { [weak self] (_, value) in
        guard let self = self, self.presentedViewController == nil else {return}
        NSObject.cancelPreviousPerformRequests(withTarget: self)
        self.perform(#selector(self.startLoading), with: nil, afterDelay: 0.2)
    }
    playerCollect.contentInset = UIEdgeInsets(top: 0, left: 0, bottom: 200, right:0)
    DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) { [weak self] in
        self?.updateByContentOffset()
        self?.startLoading()
    }

    mmPlayerLayer.getStatusBlock { [weak self] (status) in
        switch status {
        case .failed(let err):
            let alert = UIAlertController(title: "err", message: err.description, preferredStyle: .alert)
            alert.addAction(UIAlertAction(title: "OK", style: .default, handler: nil))
            self?.present(alert, animated: true, completion: nil)
        case .ready:
            print("Ready to Play")
        case .playing:
            print("Playing")
        case .pause:
            print("Pause")
        case .end:
            print("End")
        default: break
        }
    }
    mmPlayerLayer.getOrientationChange { (status) in
        print("Player OrientationChange \(status)")
    }
}

deinit {
    offsetObservation?.invalidate()
    offsetObservation = nil
    print("ViewController deinit")
}
}


func backReplaceSuperView(original: UIView?) -> UIView? {
    guard let path = self.findCurrentPath() else {
        return original
    }

    let cell = self.findCurrentCell(path: path) as! PlayerCell
    return cell.imgView
}

// add layer to temp view and pass to another controller
var passPlayer: MMPlayerLayer {
    return self.mmPlayerLayer
}
func transitionWillStart() {
}
// show cell.image
func transitionCompleted() {
    self.updateByContentOffset()
    self.startLoading()
}
}

extension ViewController: UICollectionViewDelegateFlowLayout {
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    let m = min(UIScreen.main.bounds.size.width, UIScreen.main.bounds.size.height)
    return CGSize(width: m, height: m*0.75)
}
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
   DispatchQueue.main.async { [unowned self] in
    if self.presentedViewController != nil || self.mmPlayerLayer.isShrink == true {
            //self.playerCollect.scrollToItem(at: indexPath, at: .centeredVertically, animated: true)
            //self.updateDetail(at: indexPath)
        } else {
            self.presentDetail(at: indexPath)
        }
    }
}

fileprivate func updateByContentOffset() {
    if mmPlayerLayer.isShrink {
        return
    }

    if let path = findCurrentPath(),
        self.presentedViewController == nil {
        self.updateCell(at: path)
        //Demo SubTitle
        if path.row == 0, self.mmPlayerLayer.subtitleSetting.subtitleType == nil {
            let subtitleStr = Bundle.main.path(forResource: "srtDemo", ofType: "srt")!
            if let str = try? String.init(contentsOfFile: subtitleStr) {
                self.mmPlayerLayer.subtitleSetting.subtitleType = .srt(info: str)
                self.mmPlayerLayer.subtitleSetting.defaultTextColor = .red
                self.mmPlayerLayer.subtitleSetting.defaultFont = UIFont.boldSystemFont(ofSize: 20)
            }
        }
    }
}

fileprivate func presentDetail(at indexPath: IndexPath) {
    self.updateCell(at: indexPath)
    mmPlayerLayer.resume()

    if let vc = UIStoryboard.init(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "DetailViewController") as? DetailViewController {
        vc.data = DemoSource.shared.demoData[indexPath.row]
        self.present(vc, animated: true, completion: nil)
    }
}

fileprivate func updateCell(at indexPath: IndexPath) {
    if let cell = playerCollect.cellForItem(at: indexPath) as? PlayerCell, let playURL = cell.data?.play_Url {
        // this thumb use when transition start and your video dosent start
        mmPlayerLayer.thumbImageView.image = cell.imgView.image
        // set video where to play
        mmPlayerLayer.playView = cell.imgView
        mmPlayerLayer.set(url: playURL)
    }
}

@objc fileprivate func startLoading() {
    self.updateByContentOffset()
    if self.presentedViewController != nil {
        return
    }
    // start loading video
    mmPlayerLayer.resume()
}

private func findCurrentPath() -> IndexPath? {
    let p = CGPoint(x: playerCollect.frame.width/2, y: playerCollect.contentOffset.y + playerCollect.frame.width/2)
    return playerCollect.indexPathForItem(at: p)
}

private func findCurrentCell(path: IndexPath) -> UICollectionViewCell {
    return playerCollect.cellForItem(at: path)!
}
}

extension ViewController: UICollectionViewDataSource {
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return DemoSource.shared.demoData.count
}

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    if let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "PlayerCell", for: indexPath) as? PlayerCell {
        cell.data = DemoSource.shared.demoData[indexPath.row]
        return cell
    }
    return UICollectionViewCell()
}
}

Answer 1

使用强制可选运算符 ! 是不好的做法，因为它通常会导致出现您描述的错误消息。您的 findCurrentPath 计算尚未针对水平移动进行更新。首先，将您的 findCurrentPath 方法更改为（我相信您正在努力实现的）：

private func findCurrentPath() -> IndexPath? {
    let p = CGPoint(x: playerCollect.contentOffset.x + playerCollect.frame.width/2, 
                    y: playerCollect.frame.height/2)
    return playerCollect.indexPathForItem(at: p)
}

为了防止崩溃，即使它没有完全按照您的要求进行操作，我也只清理了另外两种方法，因为有太多的强制可选运算符无法解决所有问题；将您的 findCurrentCell 方法更改为以下内容：

private func findCurrentCell(path: IndexPath) -> UICollectionViewCell? {
   return playerCollect.cellForItem(at: path)
}

最后是您的 backReplaceSuperView 方法：

 func backReplaceSuperView(original: UIView?) -> UIView? {
    guard let path = self.findCurrentPath(),
        let cell = self.findCurrentCell(path: path) as? PlayerCell else {
        return original
    }
    return cell.imgView
}

为什么当我将滚动方向从垂直更改为水平时，集合视图会崩溃？

Why does collection view crash when I change the scroll direction from vertical to horizontal?

xcode

ios

uicollectionview

swift

swift5