swift - 核心数据如何在多线程中使用 NSMangedObjectContext

问题描述

好的，我已经做了一天了，似乎无法弄清楚我做错了什么。这就是我的核心数据数据模型的样子。

这就是我的代码的样子。

class Service {
static let shared = Service()
private let numberOfPokemons = 151

func downloadPokemonsFromServer(completion: @escaping ()->()) {
    let urlString = "https://pokeapi.co/api/v2/pokemon?limit=\(numberOfPokemons)"
    guard let url = URL(string: urlString) else { return }
    var id: Int16 = 0


    URLSession.shared.dataTask(with: url) { (data, response, error) in
        if let err = error {
            print("Unable to fetch pokemon", err)
        }

        guard let data = data else { return }
        let privateContext = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)
        privateContext.parent = CoreDataManager.shared.persistentContainer.viewContext

        let decoder = JSONDecoder()
        decoder.keyDecodingStrategy = .convertFromSnakeCase

        do {
            let pokemonJSON = try decoder.decode(PokemonsJSON.self, from: data)
            pokemonJSON.pokemons.forEach { (JSONPokemon) in
                id += 1

                let pokemon = Pokemon(context: privateContext)
                pokemon.name = JSONPokemon.name
                pokemon.url = JSONPokemon.detailUrl
                pokemon.id = id

            }

            try? privateContext.save()
            try? privateContext.parent?.save()
            completion()
        } catch let err {
            print("Unable to decode PokemonJSON. Error: ",err)
            completion()
        }
    }.resume()
}

private var detailTracker = 0
func fetchMoreDetails(objectID: NSManagedObjectID) {

    guard let pokemon = CoreDataManager.shared.persistentContainer.viewContext.object(with: objectID) as? Pokemon, let urlString = pokemon.url else { return }

    print(pokemon.name)
    print()

    guard let url = URL(string: urlString) else { return }

    URLSession.shared.dataTask(with: url) { (data, response, error) in
        if let err = error {
            print("Unable to get more details for pokemon", err)
        }

        guard let data = data else { return }
        let privateContext = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)
        privateContext.parent = CoreDataManager.shared.persistentContainer.viewContext

        let decoder = JSONDecoder()
        decoder.keyDecodingStrategy = .convertFromSnakeCase

        do {
            let pokemonDetailJSON = try decoder.decode(PokemonDetailJSON.self, from: data)
            pokemonDetailJSON.types.forEach { (nestedType) in

                let type = Type(context: privateContext)
                type.name = nestedType.type.name
                type.addToPokemons(pokemon)

            }

            try? privateContext.save()
            try? privateContext.parent?.save()

        } catch let err {
            print("Unable to decode pokemon more details", err)
        }

    }.resume()
}

private var imageTracker = 0
func getPokemonImage(objectID: NSManagedObjectID) {
    guard let pokemon = CoreDataManager.shared.persistentContainer.viewContext.object(with: objectID) as? Pokemon else { return }

    let id = String(format: "%03d", pokemon.id)
    let urlString = "https://assets.pokemon.com/assets/cms2/img/pokedex/full/\(id).png"
    print(urlString)



    guard let url = URL(string: urlString) else { return }
    URLSession.shared.dataTask(with: url) { (data, response, error) in
        if let err = error {
            print("Unable to load image from session.", err)
        }

        guard let data = data else { return }
        let privateContext = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)
        privateContext.parent = CoreDataManager.shared.persistentContainer.viewContext
        pokemon.image = data

        self.imageTracker += 1

        if self.imageTracker == self.numberOfPokemons {
            try? privateContext.save()
            try? privateContext.parent?.save()
        }
    }.resume()
}
}

我有 3 个实体，分别是口袋妖怪、类型和能力。我现在不是什么都不做，所以我们可以忽略这一点。第一个函数 downloadPokemonFromServer 只是抓取前 151 个 pokemon，保存 pokemon 的名称和 url。然后我使用该 url 进入另一个 URLSession 并获取有关该 pokemon 的更多信息。这就是 fetchMoreDetails 函数的作用。但是，此功能使我的应用程序崩溃。我不知道我在这里做错了什么，当我尝试保存它时它崩溃了。

第三个函数 getPokemonImage 我进入另一个 URLSession，获取数据并将其保存到我的 pokemon 图像属性中。问题是这工作得很好。它保存到我的 CoreData 并且不会使我的应用程序崩溃。

这就是我在 ViewController 中调用它的方式。

@objc func handleRefresh() {

    if pokemonController.fetchedObjects?.count == 0 {
        Service.shared.downloadPokemonsFromServer {
            let pokemons = self.pokemonController.fetchedObjects
            pokemons?.forEach({ (pokemon) in

               Service.shared.getPokemonImage(objectID: pokemon.objectID)
               //If I uncomment the line below it will crash my app.
               //Service.shared.fetchMoreDetails(objectID: pokemon.objectID)
            })
        }
    }
     tableView.refreshControl?.endRefreshing()
}

有人请帮我弄清楚我做错了什么。非常感谢您的帮助。

标签： swiftcore-data

swift - 核心数据如何在多线程中使用 NSMangedObjectContext

问题描述

解决方案

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