我的应用中有一个视频播放器.集合视图中有一个视频列表.如果您点击其中一个单元格,则会出现一个新的视图控制器来播放所选的视频.此外,您可以在此新视图控制器中循环浏览集合视图中的所有视频,因为传递了整个列表.

问题是：
当用户在PlayerVC中时,他们可以不喜欢视频.如果他们这样做,我从Realm删除Video对象.但是,这会导致：

由于未捕获的异常’RLMException’而终止应用程序,原因是：’对象已被删除或无效.’

基本上,如果用户正在观看PlayerVC中的视频并且他不喜欢视频,我希望他们仍然能够暂时观看视频.但是当他们离开PlayerVC时,应该更新FavoritesVC中的集合视图,而不再显示该视频.

当我删除一个Video对象时,我使用了Realm的删除方法.

这是我保存Video对象列表的代码：

/// Model class that manages the ordering of `Video` objects.
final class FavoriteList: Object {
    // MARK: - Properties

    /// `objectId` is set to a static value so that only
    /// one `FavoriteList` object could be saved into Realm.
    dynamic var objectId = 0

    let videos = List<Video>()

    // MARK: - Realm Meta Information

    override class func primaryKey() -> String? {
        return "objectId"
    }
}

这是我的Video类,它有一个isFavorite属性：

final class Video: Object {
    // MARK: - Properties

    dynamic var title = ""
    dynamic var descriptionText = ""
    dynamic var date = ""
    dynamic var videoId = ""
    dynamic var category = ""
    dynamic var duration = 0
    dynamic var fullURL = ""
    dynamic var creatorSite = ""
    dynamic var creatorName = ""
    dynamic var creatorURL = ""

    // MARK: FileManager Properties (Files are stored on disk for `Video` object).

    /*
        These are file names (e.g., myFile.mp4, myFile.jpg)
    */
    dynamic var previewLocalFileName: String?
    dynamic var stitchedImageLocalFileName: String?
    dynamic var placeholderLocalFileName: String?

    /*
        These are partial paths (e.g., bundleID/Feed/myFile.mp4,     bundleID/Favorites/myFile.mp4)
        They are used to build the full path/URL at runtime.
    */
    dynamic var previewLocalFilePath: String?
    dynamic var stitchedImageLocalFilePath: String?
    dynamic var placeholderLocalFilePath: String?

    // Other code...
}

这是我在集合视图中显示Video对象的代码(注意：我使用RealmCollectionChange更新集合视图以删除和插入单元格)：

/// This view controller has a `collectioView` to show the favorites.
class FavoriteCollectionViewController: UIViewController {
    // MARK: Properties

    let favoriteList: FavoriteList = {
        let realm = try! Realm()
        return realm.objects(FavoriteList.self).first!
    }()

    // Realm notification token to update collection view.
    var notificationToken: NotificationToken?

    // MARK: Collection View

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

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: FavoritesCollectionViewCell.reuseIdentifier, for: indexPath) as! FavoritesCollectionViewCell
        cell.video = favoriteList.videos[indexPath.item]

        return cell
    }

    // I pass this lst forward to the PlayerVC
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        if let playerVC = self.storyboard?.instantiateViewController(withIdentifier: "PlayerViewController") as? PlayerViewController {
            // I pass the videos here.
            playerVC.videos = favoriteList.videos
            self.parent?.present(playerVC, animated: true, completion: nil)
        }
    }

    // MARK: Realm Notifications


    func updateUI(with changes: RealmCollectionChange<List<Video>>) {
        // This is code to update the collection view.
    }
}

最后,这是允许用户在所有Video对象之间播放和循环的代码：

/// This view controller uses `AVFoundation` to play the videos from `FavoriteCollectionViewController`.
class PlayerViewControllerr: UIViewController {

    /// This `videos` is passed from `FavoriteCollectionViewController`
    var videos = List<Video>()

    // HELP: The app crashes here if I unfavorite a `Video`.
    @IBAction func didToggleStarButton(_ sender: UIButton) {
        let realm = try! Realm()
        try! realm.write {
            let videoToDelete = videos[currentIndexInVideosList] /// Get the video that is currently playing
            realm.delete(videoToDelete)
        }
    }
}

最终,我希望从Realm中完全删除不受欢迎的Video对象.在这种情况下,只是不确定如何/何时这样做.

有什么想法吗？

更新1

解决这个问题的一个选择是：

>制作视频副本的非托管副本,并使用该副本为视图控制器的UI供电.

我认为这可能有效的方式是这样的：

> PlayerVC将收到两个List,原始的一个保存在Realm中,并且该列表的副本为UI提供动力.让我们调用列表favoriteList和copyList.
>所以在didToggleStarButton里面我们会这样做：

码：

/// This view controller uses `AVFoundation` to play the videos from `FavoriteCollectionViewController`.
class PlayerViewControllerr: UIViewController {

    /// A button to allow the user to favorite and unfavorite a `Video`
    @IBOutlet weak var starButton: UIButton!

    /// This is passed from `FavoriteCollectionViewController`
    var favoriteList: FavoriteList!

    /// A copy of the `FavoriteList` videos to power the UI.
    var copiedList: List<Video>!

    var currentIndexOfVideoInCopiedList: Int!

    override func viewDidLoad() {
        super viewDidLoad()

        // Make a copy of the favoriteList to power the UI.
        var copiedVideos = [Video]()

        for video in favoriteList.videos {
            let unmanagedVideo = Video(value: video)
            copiedVideos.append(unmanagedVideo)
        }

        self.copiedList.append(copiedVideos)
    }

    // HELP: The app crashes here if I unfavorite a `Video`.
    @IBAction func didToggleStarButton(_ sender: UIButton) {
        // Do the unfavoriting and favoriting here.


        // An example of unfavoriting:
        let realm = try! Realm()
        try! realm.write {
            let videoToDeleteFromFavoriteList = favoriteList.videos[currentIndexOfVideoInCopiedList] /// Get the video that is currently playing
            realm.delete(videoToDeleteFromOriginalList)
        }

        // Update star button to a new image depending on if the `Video` is favorited or not.
        starButton.isSelected = //... update based on if the `Video` in the `FavoriteList` or not.
    }
}

有什么想法吗？

最佳答案 出于许多架构原因,这个绝对是棘手的.

你是对的,你可以简单地从FavoriteList.videos中删除对象,然后在关闭控制器时从Realm中正确删除它,但你是对的,如果用户点击主页按钮,或者应用程序崩溃之前那么,你最终会得到一个无头的视频对象.您需要能够确保您可以跟踪它.

您可以考虑一些事情.

>将一个isDeleted属性添加到Video类.当用户不喜欢视频时,从FavoriteList.videos中删除Video对象,将该属性设置为true,但将其保留在Realm中.稍后(当应用程序退出或视图控制器被解除时),您可以对isDeleted为true的所有对象执行常规查询,然后删除它们(这解决了无头问题).
>由于您的体系结构需要依赖于可以从其下删除的模型的视图控制器,根据您从该Video对象使用的信息量,制作视频副本的非托管副本并使用它可能更安全那一个为视图控制器的UI供电.您可以通过执行let unmanagedVideo = Video(value：video)来创建现有Realm对象的新副本.