swift - 无法使用 CoreData 'NSManagedObject' 获取数据没有成员 'fetch'
问题描述
我是 swift 和 Xcode 12 的初学者，在创建项目时忘记检查选项核心数据后，我试图在我的项目中正确实现核心数据，我操作了我的 appDelegate.swift 并且我写了几行关于核心数据功能，但我仍然面临诸如错误类型'NSManagedObject'没有成员'fetch'之类的问题，我觉得我没有正确实现核心数据
经过几次操作，这里是我的 AppDelegate.swift ：
//
// AppDelegate.swift
// Bicycall
//
// Created by Jamil Joo on 1/12/2020.
//
import UIKit
import CoreData
@main
class AppDelegate: UIResponder, UIApplicationDelegate {
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
// Override point for customization after application launch.
return true
}
// MARK: UISceneSession Lifecycle
func application(_ application: UIApplication, configurationForConnecting connectingSceneSession: UISceneSession, options: UIScene.ConnectionOptions) -> UISceneConfiguration {
// Called when a new scene session is being created.
// Use this method to select a configuration to create the new scene with.
return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)
}
func application(_ application: UIApplication, didDiscardSceneSessions sceneSessions: Set<UISceneSession>) {
// Called when the user discards a scene session.
// If any sessions were discarded while the application was not running, this will be called shortly after application:didFinishLaunchingWithOptions.
// Use this method to release any resources that were specific to the discarded scenes, as they will not return.
}
// MARK: - Core Data stack
lazy var persistentContainer: NSPersistentContainer = {
/*
The persistent container for the application. This implementation
creates and returns a container, having loaded the store for the
application to it. This property is optional since there are legitimate
error conditions that could cause the creation of the store to fail.
*/
let container = NSPersistentContainer(name: "Bicycall")
container.loadPersistentStores(completionHandler: { (storeDescription, error) in
if let error = error as NSError? {
// Replace this implementation with code to handle the error appropriately.
// fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
/*
Typical reasons for an error here include:
* The parent directory does not exist, cannot be created, or disallows writing.
* The persistent store is not accessible, due to permissions or data protection when the device is locked.
* The device is out of space.
* The store could not be migrated to the current model version.
Check the error message to determine what the actual problem was.
*/
fatalError("Unresolved error \(error), \(error.userInfo)")
}
})
return container
}()
// MARK: - Core Data Saving support
func saveContext () {
let context = persistentContainer.viewContext
if context.hasChanges {
do {
try context.save()
} catch {
// Replace this implementation with code to handle the error appropriately.
// fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
let nserror = error as NSError
fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
}
}
}
}
这是我使用核心数据的控制器：
//
// login.swift
// Bicycall
//
// Created by Jamil Joo on 2/12/2020.
//
import UIKit
import CoreData
class login: UIViewController {
var id: Int?
var name: String?
var lastname: String?
var email:String?
var password:String?
var phone:String?
override func viewDidLoad() {
super.viewDidLoad()
self.DeleteAllData()
// Do any additional setup after loading the view.
}
//widgets
@IBOutlet weak var txtEmail: UITextField!
@IBOutlet weak var txtPassword: UITextField!
//Actions
@IBAction func btnLogin(_ sender: Any){
//get
/*
guard let url = URL(string: "http://localhost:3000/bikes") else {
return
}
let session = URLSession.shared
session.dataTask(with: url) { ( data , response ,error) in
if let response = response {
print(response)
}
if let data = data {
print(data)
do
{
let json = try JSONSerialization.jsonObject(with: data, options: [])
print(json)
}catch{
print(error)
}
}
}.resume()
*/
//post
guard let url = URL(string: "http://localhost:3000/login") else {
return
}
let bodyparameters = ["email": txtEmail.text, "password": txtPassword.text]
var request = URLRequest(url: url)
request.httpMethod = "POST"
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
guard let httpBody = try? JSONSerialization.data(withJSONObject: bodyparameters, options: []) else{
return
}
request.httpBody = httpBody
let session = URLSession.shared
session.dataTask(with: request) { (data,response,error) in
if let response = response {
print(response)
}
if let data = data {
do {
//let json = try JSONSerialization.jsonObject(with: data, options: [])
// print(json);
print(data)
let user = try JSONDecoder().decode(User.self, from: data)
DispatchQueue.main.async {
self.id = user.user_id
self.name = user.name
self.lastname = user.lastname
self.email = user.email
self.password = user.password
self.phone = user.phone
print(self.id!)
print(self.email!)
if(user.user_id != 0){
//self.saveUser(user)
self.performSegue(withIdentifier: "HomeSegue", sender: "nil")
self.saveUser()
}else{
let alert = UIAlertController(title: "Login Failed", message: "Wrong credentials", preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "Ok", style: .default, handler: nil))
alert.addAction(UIAlertAction(title: "Cancel", style: .cancel, handler: nil))
self.present(alert, animated: true)
}
}
}catch{
print(error)
}
}
}.resume()
}
func DeleteAllData(){
let appDelegate = UIApplication.shared.delegate as! AppDelegate
let managedContext = appDelegate.persistentContainer.viewContext
let DelAllReqVar = NSBatchDeleteRequest(fetchRequest: NSFetchRequest<NSFetchRequestResult>(entityName: "Users"))
do {
try managedContext.execute(DelAllReqVar)
}
catch {
print(error)
}
}
func saveUser() {
let appDelegate = UIApplication.shared.delegate as! AppDelegate
//represente l'ORM
let persistentContainer = appDelegate.persistentContainer
let managedContext = persistentContainer.viewContext
let entityDescription = NSEntityDescription.entity(forEntityName: "Users" , in: managedContext)
let object = NSManagedObject(entity: entityDescription! , insertInto: managedContext )
object.setValue(id! , forKey: "user_id" )
object.setValue(email! , forKey: "email" )
object.setValue(password! , forKey: "password" )
object.setValue(name! , forKey: "name" )
object.setValue(lastname! , forKey: "lastname" )
object.setValue(phone! , forKey: "phone" )
do {
try managedContext.save()
print("INSERT SUCCESSFULLY")
print(id!)
}
catch {
print("INSERT ERROR")
}
}
func DisplayData() {
let appDelegate = UIApplication.shared.delegate as! AppDelegate
//represente l'ORM
let persistentContainer = appDelegate.persistentContainer
let managedContext = persistentContainer.viewContext //retourne NSManagedObject toujours
//la requete retourne un NSManagedObject
let request = NSFetchRequest<NSManagedObject>(entityName : "Users")
//execution de la requete
do {
let result = try NSManagedObject.fetch(request)
for item in result {
favourites.append(item.value(forKey: "MovieName") as! String)
item.value()
}
}
catch {
print("NO DATA FOUND , Error")
}
}
@IBAction func btnSignup(_ sender: Any) {
performSegue(withIdentifier: "signupSegue", sender: "nil")
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
}
我要做的是修复我的项目CoreData并修复可以修复的内容以防止我在控制器中获得的错误
ps：我已经创建了一个数据模型Users
解决方案
该错误是一个错字并且非常清楚：
你不能调用fetch类型， NSManagedObject你必须调用它的NSManagedObjectContext 实例。
代替
let result = try NSManagedObject.fetch(request)
和
let result = try managedContext.fetch(request)
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