NSFetchedResultsController 'didChange' 使用新的 CollectionDiffing 导致奇怪的更改操作导致崩溃
NSFetchedResultsController 'didChange' using new CollectionDiffing causes strange change operations that lead to a crash
演示崩溃的示例项目：https://github.com/d3mueller/TestProjectFetchedResultsController
我有一个简单的 CoreData 设置，有两个 entities:
City，具有一对多关系incidentRoads到Road（删除城市时设置为Cascade）Road，具有一对多关系 cities 到 City
例如，我添加了两个 Cities 和一个 Road "connects" 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。
当我继续删除两个 cities 之一，而 NSFetchedResultsController 观察所有内容时，应用程序因 Index out of range error 而崩溃，同时尝试更新 didChange 获取结果控制器委托的方法：
Fatal error: Index out of range
我正在使用新的 API 获取结果控制器的委托来通过 CollectionDifference:
跟踪更改
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChangeContentWith diff: CollectionDifference<NSManagedObjectID>)
并且在删除了其中一个cities之后，那个方法被调用了很多次，有奇怪的插入和删除（我认为这对post 这些没有调试器的上下文。我在下面添加了一个示例项目）。
正在使用看起来很奇怪的 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))
我期望的 diff 只是删除数组中的第一个元素（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。第一个remove是和自己关联的？最后一个插入与第二个删除相关联。我不明白。我认为问题就出在这里。有什么想法吗？
我的视图控制器看起来像这样（我评论了发生崩溃的地方）：
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（我在其中设置对象和东西来测试所有内容）：
//
// 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，如果这有点令人困惑，我不知道如何正确解释这个问题（我什至不知道问题是什么）。如果您需要更多信息，请告诉我。
非常感谢您的帮助。
好吧，事实证明我只是个傻瓜。在遍历 diff 中的更改时，我错误地认为 .insert 情况下的 associatedWith 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)
}
...
这是导致崩溃的原因，因为 associatedWith 实际上是 .remove 与其相关联的更改的索引，表明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: {[=12=].objectID == objectID})!
....
这不是最优的，它为我不喜欢的方法增加了线性时间复杂度。但是我找不到获取元素实际旧位置的方法。由于删除了 city 对象，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。但是我要为此打开另一个问题，因为这是题外话。
演示崩溃的示例项目：https://github.com/d3mueller/TestProjectFetchedResultsController
我有一个简单的 CoreData 设置，有两个 entities:
City，具有一对多关系incidentRoads到Road（删除城市时设置为Cascade）Road，具有一对多关系cities到City
例如，我添加了两个 Cities 和一个 Road "connects" 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。
当我继续删除两个 cities 之一，而 NSFetchedResultsController 观察所有内容时，应用程序因 Index out of range error 而崩溃，同时尝试更新 didChange 获取结果控制器委托的方法：
Fatal error: Index out of range
我正在使用新的 API 获取结果控制器的委托来通过 CollectionDifference:
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChangeContentWith diff: CollectionDifference<NSManagedObjectID>)
并且在删除了其中一个cities之后，那个方法被调用了很多次，有奇怪的插入和删除（我认为这对post 这些没有调试器的上下文。我在下面添加了一个示例项目）。
正在使用看起来很奇怪的 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))
我期望的 diff 只是删除数组中的第一个元素（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。第一个remove是和自己关联的？最后一个插入与第二个删除相关联。我不明白。我认为问题就出在这里。有什么想法吗？
我的视图控制器看起来像这样（我评论了发生崩溃的地方）：
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（我在其中设置对象和东西来测试所有内容）：
//
// 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，如果这有点令人困惑，我不知道如何正确解释这个问题（我什至不知道问题是什么）。如果您需要更多信息，请告诉我。
非常感谢您的帮助。
好吧，事实证明我只是个傻瓜。在遍历 diff 中的更改时，我错误地认为 .insert 情况下的 associatedWith 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)
}
...
这是导致崩溃的原因，因为 associatedWith 实际上是 .remove 与其相关联的更改的索引，表明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: {[=12=].objectID == objectID})!
....
这不是最优的，它为我不喜欢的方法增加了线性时间复杂度。但是我找不到获取元素实际旧位置的方法。由于删除了 city 对象，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。但是我要为此打开另一个问题，因为这是题外话。