我试图从我的Viewcontroller创建一个数组，使其等于我的核心数据已保存的对象。我正在使用核心数据，并创建了一个名为Pokemon的实体，该实体具有3个属性名称， id 和生成。在应用程序委托中，我使用以下函数从API中获取Pokemon。这是我解析数据并保存上下文的操作:
typealias DownloadCompleted = () -> ()
var pokemonId: Int16 = 0
func fetchPokemon(url: String, completed: @escaping DownloadCompleted) {
let context = coreData.persistentContainer.viewContext
let url = URLRequest(url: URL(string: url)!)
let task = URLSession.shared.dataTask(with: url) { (data, repsonse, error) in
if error != nil {
print(error!)
}
do {
let jsonResult = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as! NSDictionary
let jsonArray = jsonResult.value(forKey: "results") as! [[String: Any]]
for pokemonData in jsonArray {
self.pokemonId += 1
if self.pokemonId > 721 {
self.coreData.saveContext()
return
}
guard let name = pokemonData["name"] as? String else {
return
}
let pokemon = Pokemon(context: context)
pokemon.name = name
pokemon.id = self.pokemonId
print("Name: \(pokemon.name) Id:\(self.pokemonId)")
if self.pokemonId <= 151 {
pokemon.generation = 1
} else if self.pokemonId <= 251 {
pokemon.generation = 2
} else if self.pokemonId <= 386 {
pokemon.generation = 3
} else if self.pokemonId <= 493 {
pokemon.generation = 4
} else if self.pokemonId <= 649 {
pokemon.generation = 5
} else if self.pokemonId <= 721 {
pokemon.generation = 6
}
}
guard let nextURL = jsonResult.value(forKey: "next") as? String else {
self.coreData.saveContext()
return
}
DispatchQueue.main.async {
self.fetchPokemon(url: nextURL, completed: {
self.coreData.saveContext()
})
completed()
}
} catch let err {
print(err.localizedDescription)
}
}
task.resume()
}
这就是我在appDelegate中称呼它的方式。真的不知道在fetchPokemon中间该做什么或如何在另一个视图控制器中调用它。所以我将其留为空白，不确定是否与我遇到的问题有关。
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
let context = self.coreData.persistentContainer.viewContext
let pokemonListVC = self.window?.rootViewController as! PokemonListVC
pokemonListVC.context = context
fetchPokemon(url: pokemonAPI) {
}
return true
}
我正在应用商店中使用此SQL-Light只读应用。我检查了数据，所有721宠物小精灵都在保存。现在，我不知道如何使我的视图控制器中的数组等于保存的所有721 Pokemon。我将此代码添加到我的viewController中。
class PokemonListVC: UIViewController {
weak var context: NSManagedObjectContext! {
didSet {
return pokemon = Pokemon(context: context)
}
}
var pokemon: Pokemon? = nil
lazy var pokemons = [Pokemon]()
override func viewDidLoad() {
super.viewDidLoad()
loadData()
}
func loadData() {
pokemons = pokemon!.loadPokemon(generation: 1, context: context)
}
}
我已经创建了我的Pokemon实体的扩展，并添加了一个功能loadPokemon，它可以按代过滤Pokemon。这是代码。
extension Pokemon {
func loadPokemon(generation: Int16 = 0, context: NSManagedObjectContext) -> [Pokemon] {
let request: NSFetchRequest<Pokemon> = Pokemon.fetchRequest()
request.predicate = NSPredicate(format: "generation = %@", generation)
request.sortDescriptors = [NSSortDescriptor(key: "name", ascending: true)]
do {
let pokemons = try context.fetch(request)
print("My Pokemon count: \(pokemons.count)")
return pokemons
} catch let err {
print(err.localizedDescription)
}
return []
}
}
当我在ViewController中调用loadData时，它崩溃了。数组计数为0，英雄扩展中的数组计数也为0。所以我不怎么使我的数组等于从coreData保存的Pokemon。
非常感谢您提供的任何帮助。 :)
这是我的deleteRecords代码，它也在我的appDelegate中。应用启动时，这将删除所有记录。我在fetchPokemons之前的didFinishLaunchingWithOption函数的开头就调用了此方法。
func deleteRecords() {
let context = coreData.persistentContainer.viewContext
let pokemonRequest: NSFetchRequest<Pokemon> = Pokemon.fetchRequest()
var deleteRequest: NSBatchDeleteRequest
var deleteResults: NSPersistentStoreResult
do {
deleteRequest = NSBatchDeleteRequest(fetchRequest: pokemonRequest as! NSFetchRequest<NSFetchRequestResult>)
deleteResults = try context.execute(deleteRequest)
} catch let err {
print(err.localizedDescription)
}
}
最佳答案
正如您所说的那样，您可以确保所有的pockemon记录都正确地存储在coredata中，您只需提供获取请求就可以从代码数据中获取记录。我已经创建了用于联系人存储的演示，并且可以通过此获取请求获取所有联系人，您可以在要获取所有记录的ViewController中尝试此代码。
let appDelegate = UIApplication.shared.delegate as! AppDelegate
let managedContext = appDelegate.persistentContainer.viewContext
let fetchRequest = NSFetchRequest<NSManagedObject> (entityName: "Pokemon")
do {
arrPockemon = try managedContext.fetch(fetchRequest)
}catch let error as NSError {
showAlert(string: error.localizedDescription)
}
尝试先获取所有记录，如果获取全部，则尝试过滤扩展名和全部。希望对您有帮助。你可以从这里学习https://code.tutsplus.com/tutorials/core-data-and-swift-core-data-stack--cms-25065
在userDefault上保存标志。
//check for first time when app is installed first time(first time flag is not present so)
let userDefault = UserDefaults.standard.dictionaryRepresentation()
if userDefault.keys.contains("isDataAvailable") {
//key is availebe so check it
if userDefault["isDataAvailable"] as! String == "1"{
//no need to call server for data
}else{
//fetch data from server
// once you get data from server make isDataAvailable flage as 1
UserDefaults.standard.setValue("1", forKey: "isDataAvailable")
UserDefaults.standard.synchronize()
}
}
else{
//flag is not avalable so call server for data
// once you get data from server make isDataAvailable flage as 1
UserDefaults.standard.setValue("1", forKey: "isDataAvailable")
UserDefaults.standard.synchronize()
}