示例代码更改为守卫并指出崩溃

Question

这是我的代码

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


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


func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell
{
    //let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "FullImageCell", for: indexPath) as! FullImageCollectionViewCell

     guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "FullImageCell", for: indexPath) as? FullImageCollectionViewCell else {
        fatalError()
    }

    let indexPath = indexPath.row
    //UserDefaults.standard.set(indexPath, forKey: "INDEX")
    //UserDefaults.standard.synchronize()

    self.value = indexPath

    let videoStr = NSString.init(format: "http://52.2.212.171/wallpaper/admin/%@", self.getVideosArray.object(at: indexPath) as! String)
    self.downloadVideoLinkAndCreateAsset(videoStr as String)

    return cell
}


func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: IndexPath) -> CGSize
{
    return CGSize(width: self.collectionView.frame.size.width, height: self.collectionView.frame.size.height)
}


func downloadVideoLinkAndCreateAsset(_ videoLink: String)
{
    self.bgView.isHidden = false
    // use guard to make sure you have a valid url
    guard let videoURL = URL(string: videoLink) else { return }

    let documentsDirectoryURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
    // check if the file already exist at the destination folder if you don't want to download it twice
    if !FileManager.default.fileExists(atPath: documentsDirectoryURL.appendingPathComponent(videoURL.lastPathComponent).path) {

        // set up your download task
        URLSession.shared.downloadTask(with: videoURL) { (location, response, error) -> Void in

            // use guard to unwrap your optional url
            guard let location = location else { return }

            // create a deatination url with the server response suggested file name
            let destinationURL = documentsDirectoryURL.appendingPathComponent(response?.suggestedFilename ?? videoURL.lastPathComponent)
            do {

                try FileManager.default.moveItem(at: location, to: destinationURL)

                self.loadVideoWithVideoURL(destinationURL)
            }
            catch let error as NSError
            {
                print(error.localizedDescription)
            }

        }.resume()
    }
    else
    {
        let getPathUrl = documentsDirectoryURL.appendingPathComponent(videoURL.lastPathComponent)

        self.loadVideoWithVideoURL(getPathUrl)
    }

}


func loadVideoWithVideoURL(_ videoURL: URL) {
    let asset = AVURLAsset(url: videoURL)
    let generator = AVAssetImageGenerator(asset: asset)
    generator.appliesPreferredTrackTransform = true
    let time = NSValue(time: CMTimeMakeWithSeconds(CMTimeGetSeconds(asset.duration)/2, asset.duration.timescale))
    generator.generateCGImagesAsynchronously(forTimes: [time]) { [weak self] _, image, _, _, _ in
        if let image = image, let data = UIImagePNGRepresentation(UIImage(cgImage: image)) {
            let urls = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
            let imageURL = urls[0].appendingPathComponent("image.jpg")
            try? data.write(to: imageURL, options: [.atomic])

            let image = imageURL.path
            let mov = videoURL.path
            let output = FilePaths.VidToLive.livePath
            let assetIdentifier = UUID().uuidString
            let _ = try? FileManager.default.createDirectory(atPath: output, withIntermediateDirectories: true, attributes: nil)
            do {
                try FileManager.default.removeItem(atPath: output + "/IMG.JPG")
                try FileManager.default.removeItem(atPath: output + "/IMG.MOV")

            } catch {

            }
            JPEG(path: image).write(output + "/IMG.JPG",
                                    assetIdentifier: assetIdentifier)
            QuickTimeMov(path: mov).write(output + "/IMG.MOV",
                                          assetIdentifier: assetIdentifier)

            guard let targetSize = self?.collectionView.bounds.size else
            {
                fatalError()
                //return
            }

            PHLivePhoto.request(withResourceFileURLs: [ URL(fileURLWithPath: FilePaths.VidToLive.livePath + "/IMG.MOV"), URL(fileURLWithPath: FilePaths.VidToLive.livePath + "/IMG.JPG")],
                                placeholderImage: nil,
                                targetSize: targetSize,
                                contentMode: PHImageContentMode.aspectFit,
                                resultHandler: { (livePhoto, info) -> Void in

                                    guard let indexValue = self?.value else
                                    {
                                        fatalError()
                                        //return
                                    }

                                    let indexPath = IndexPath.init(row: indexValue, section: 0)
                                    print(indexPath)

                                    guard let cell = self?.collectionView.cellForItem(at: indexPath as IndexPath) as? FullImageCollectionViewCell
                                    else
                                    {
                                        fatalError()
                                        //return
                                    }
                                    cell.fullImage.livePhoto = livePhoto

                                    self?.bgView.isHidden = true
                                    //self?.livePhotoView.livePhoto = livePhoto

                                    //self?.collectionView.reloadData()
            })
        }
    }
}

在这里，我在 loadVideoWithVideoUrl 函数的单元格中设置实时照片。我更改为从 !守卫。并且应用程序在 func loadVideoWithVideoURL(_ videoURL: URL) 结束时崩溃，我将值设置为单元格。

guard let cell = self?.collectionView.cellForItem(at: indexPath as IndexPath) as? FullImageCollectionViewCell
                else
                 {
                     fatalError()
                      //return
                 }

Answer 1

我怀疑你的崩溃是因为这行中的!：

let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "FullImageCell", for: indexPath) as! FullImageCollectionViewCell

改成：

guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "FullImageCell", for: indexPath) as? FullImageCollectionViewCell else {
  fatalError()

  return
}

如果它在执行fatalError() 行时崩溃，那么问题是cell 到FullImageCollectionViewCell 的转换失败。