演示崩溃的示例项目：https://github.com/d3mueller/TestProjectFetchedResultsController
我有两个entities的简单CoreData设置：City，与incidentRoads的关系为Road（删除城市时设置为Cascade）Road，cities与City有很多关系
例如，我添加了两个Cities和一个Road“连接”两个城市。在我的ViewController中，我设置了两个NSFetchedResultsController，它们负责使所述视图控制器中的两个数组var cities: [City]和var roads: [Road]保持最新。
当我继续并删除两个cities之一时，同时NSFetchedResultsController观察到所有内容，当尝试在获取的结果控制器的委托的Index out of range error方法中更新数组时，由于didChange导致应用程序崩溃：
致命错误：索引超出范围
我正在使用获取的结果控制器的委托的新API通过CollectionDifference跟踪更改：
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChangeContentWith diff: CollectionDifference<NSManagedObjectID>)
并且在删除
cities之一之后，多次调用该方法，并进行奇怪的插入和删除操作（我认为在没有调试器上下文的情况下将其张贴在这里不会有帮助。我添加了一个示例项目下面）。用看起来非常奇怪的
diff调用该方法：remove(offset: 1, element: 0xcb6b486b0bd166fe <x-coredata://E2AA7DB9-7A1F-4130-9AE4-A9D0DC695159/City/p2>, associatedWith: Optional(0))
remove(offset: 0, element: 0xcb6b486b0bdd66fe <x-coredata://E2AA7DB9-7A1F-4130-9AE4-A9D0DC695159/City/p1>, associatedWith: nil)
insert(offset: 0, element: 0xcb6b486b0bd166fe <x-coredata://E2AA7DB9-7A1F-4130-9AE4-A9D0DC695159/City/p2>, associatedWith: Optional(1))
我希望
diff看起来只是数组中第一个元素的一个删除（删除的第一个city）。但这对我来说没有任何意义。我什至不明白这些实际上试图告诉我什么。第一次删除与自己相关联吗？最后插入与第二个删除相关联。我不明白我认为问题就在这里。有任何想法吗？我的视图控制器如下所示（我评论了崩溃发生的位置）：
class ViewController: UIViewController, NSFetchedResultsControllerDelegate {
public var cities: [City] = []
private lazy var citiesResultsController: NSFetchedResultsController<City> = {
let request: NSFetchRequest<City> = City.fetchRequest()
request.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: true)]
let controller = NSFetchedResultsController(fetchRequest: request, managedObjectContext: AppDelegate.managedObjectContext, sectionNameKeyPath: nil, cacheName: nil)
controller.delegate = self
return controller
}()
public var roads: [Road] = []
private lazy var roadsResultsController: NSFetchedResultsController<Road> = {
let request: NSFetchRequest<Road> = Road.fetchRequest()
request.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: true)]
let controller = NSFetchedResultsController(fetchRequest: request, managedObjectContext: AppDelegate.managedObjectContext, sectionNameKeyPath: nil, cacheName: nil)
controller.delegate = self
return controller
}()
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChangeContentWith diff: CollectionDifference<NSManagedObjectID>) {
if controller === citiesResultsController {
for change in diff {
switch change {
case .insert(offset: let newPosition, element: _, associatedWith: let oldPosition):
if let oldPosition = oldPosition {
// was moved
// HERE IT CRASHES
let city = cities.remove(at: oldPosition)
cities.insert(city, at: newPosition)
} else {
// was inserted
let city = citiesResultsController.object(at: IndexPath(item: newPosition, section: 0))
cities.insert(city, at: newPosition)
}
case .remove(offset: let position, element: _, associatedWith: let associatedWith):
if associatedWith == nil {
_ = cities.remove(at: position)
}
}
}
} else {
for change in diff {
switch change {
case .insert(offset: let newPosition, element: _, associatedWith: let oldPosition):
if let oldPosition = oldPosition {
// was moved
let road = roads.remove(at: oldPosition)
roads.insert(road, at: newPosition)
} else {
// was inserted
let road = roadsResultsController.object(at: IndexPath(item: newPosition, section: 0))
roads.insert(road, at: newPosition)
}
case .remove(offset: let position, element: _, associatedWith: let associatedWith):
if associatedWith == nil {
_ = roads.remove(at: position)
}
}
}
}
}
override func viewDidLoad() {
super.viewDidLoad()
try? citiesResultsController.performFetch()
cities = citiesResultsController.fetchedObjects ?? []
try? roadsResultsController.performFetch()
roads = roadsResultsController.fetchedObjects ?? []
DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(5)) {
print("Now")
AppDelegate.managedObjectContext.delete(AppDelegate.cityA)
try! AppDelegate.managedObjectContext.save()
}
}
}
还有我的appDelegate（在其中设置对象和东西以测试所有内容）：
//
// AppDelegate.swift
// TestProject
//
// Created by Dennis Müller on 23.09.19.
// Copyright © 2019 Dennis Müller. All rights reserved.
//
import UIKit
import CoreData
@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
public static var managedObjectContext: NSManagedObjectContext {
return (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
}
public static var cityA: City!
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
// Override point for customization after application launch.
if !UserDefaults.standard.bool(forKey: "setup") {
UserDefaults.standard.set(true, forKey: "setup")
let cityA = City(context: persistentContainer.viewContext)
cityA.name = "cityA"
cityA.creationDate = Date()
let cityB = City(context: persistentContainer.viewContext)
cityB.name = "cityB"
cityB.creationDate = Date()
let road = Road(context: persistentContainer.viewContext)
road.creationDate = Date()
road.addToCities(cityA)
road.addToCities(cityB)
saveContext()
}
let request: NSFetchRequest<City> = City.fetchRequest()
request.predicate = NSPredicate(format: "name == %@", "cityA")
AppDelegate.cityA = try! persistentContainer.viewContext.fetch(request).first!
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: "TestProject")
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)")
}
}
}
}
抱歉，这有点令人困惑，我不知道如何正确解释问题（我什至不知道问题出在哪里）。如果您需要更多信息，请与我们联系。
非常感谢您的帮助。
最佳答案
好吧，原来我只是个傻瓜。遍历diff中的更改时，我错误地认为associatedWith案例的.insert是应该移动的元素的旧索引：
...
case .insert(offset: let newPosition, element: _, associatedWith: let oldPosition):
// I called the associatedWith 'oldPosition'
if let oldPosition = oldPosition {
// was moved
// HERE IT CRASHES
let city = cities.remove(at: oldPosition)
cities.insert(city, at: newPosition)
} else {
// was inserted
let city = citiesResultsController.object(at: IndexPath(item: newPosition, section: 0))
cities.insert(city, at: newPosition)
}
...
这导致崩溃，因为
associatedWith实际上是与其连接的.remove更改的索引，以指示它实际上是移动而不是插入。所以我替换了这个：
case .insert(offset: let newPosition, element: _, associatedWith: let oldPosition):
...
let city = cities.remove(at: oldPosition)
...
有了这个：
case .insert(offset: let newPosition, element: let objectID, associatedWith: let associatedWith):
...
let city = cities.first(where: {$0.objectID == objectID})!
....
这不是最佳选择，它给我不喜欢的方法增加了线性时间复杂度。但是我找不到一种方法来获取元素的实际旧位置。由于删除了
city对象，因此移动操作变得更加复杂。我不明白为什么首先要采取行动。它所要做的就是删除一个城市，仅此而已。但是我将为此提出另一个问题，因为这是题外话。关于ios - 使用新的CollectionDiffing的NSFetchedResultsController'didChange'会导致奇怪的更改操作，从而导致崩溃，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/58070333/