【发布时间】：2020-07-05 15:51:29
【问题描述】：
一个非常简单的 CoreData 应用程序：下面提供的所有代码。
- 使用 CoreData 模板单视图应用程序启动。
- 2 个实体，每个实体都有一个字符串属性：Message(title) 和 Post(name)
一个 NavigationView 包含
- 导航链接到消息列表
- 导航链接到帖子列表
每个链接的 ListView（消息/帖子）都有
- 向列表中添加项目的按钮
- 从列表中删除所有项目的按钮
现在，当您在模拟器（任何 iOS 13.x 版本）上运行此应用程序时，所有操作都按上述说明运行。
但是在运行 iOS 13.4 的设备上
- 点击“消息”
- 创建/删除消息工作正常，SwiftUi 视图立即更新。
- 点按“返回”
- 再次点击“消息”。虽然仍然可以正常创建/删除消息：调试器现在显示警告：“环境中的上下文未连接到持久存储协调器：NSManagedObjectContext:0x280ed72c0
- 点击“帖子” ==> 应用程序因 EXC_BREAKPOINT 崩溃（代码=1，子代码=0x1f3751f08）
您也可以先从帖子开始该过程。然后在消息列表视图上发生同样的崩溃。
我坚信这是 iOS 13.4 的错误，因为类似的代码在 Xcode 11.3 / iOS 13.3 上运行良好。
有人知道解决方法或解决方法吗？
这里是完整项目的链接：Full Xcode Project
内容视图：
import SwiftUI
import CoreData
struct MessageList: View {
@Environment(\.managedObjectContext) var moc
@FetchRequest(entity: Message.entity(), sortDescriptors: [])
var messages: FetchedResults<Message>
var body: some View {
List() {
ForEach(messages, id: \.self) { message in
Text(message.title ?? "?")
}
}
.navigationBarItems(trailing:
HStack(spacing: 16) {
Button(action: deleteMessages) {
Image(systemName: "text.badge.minus")
}
Button(action: addMessage) {
Image(systemName: "plus.app")
}
}
)
}
func addMessage() {
let m = Message(context: moc)
m.title = "Message: \(Date())"
try! moc.save()
}
func deleteMessages() {
messages.forEach {
moc.delete($0)
}
}
}
struct PostList: View {
@Environment(\.managedObjectContext) var moc
@FetchRequest(entity: Post.entity(), sortDescriptors: [])
var posts: FetchedResults<Post>
var body: some View {
List {
ForEach(0..<posts.count, id: \.self) { post in
Text(self.posts[post].name ?? "?")
}
}
.navigationBarItems(trailing:
HStack(spacing: 16) {
Button(action: deletePosts) {
Image(systemName: "text.badge.minus")
}
Button(action: addPost) {
Image(systemName: "plus.app")
}
}
)
}
func addPost() {
let p = Post(context: moc)
p.name = "Post \(UUID().uuidString)"
try! moc.save()
}
func deletePosts() {
posts.forEach {
moc.delete($0)
}
try! moc.save()
}
}
struct ContentView: View {
@Environment(\.managedObjectContext) var moc
var body: some View {
NavigationView {
VStack(alignment: .leading){
NavigationLink(destination: MessageList()) {
Text("Messages")
}.padding()
NavigationLink(destination: PostList()) {
Text("Posts")
}.padding()
Spacer()
}
}.navigationViewStyle(StackNavigationViewStyle())
}
}
struct ContentView_Previews: PreviewProvider {
static let moc = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
static var previews: some View {
ContentView()
.environment(\.managedObjectContext, moc)
}
}
模型截图：
SceneDelegate（与模板相同，提供完整性）：
class SceneDelegate: UIResponder, UIWindowSceneDelegate {
var window: UIWindow?
func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
let contentView = ContentView().environment(\.managedObjectContext, context)
if let windowScene = scene as? UIWindowScene {
let window = UIWindow(windowScene: windowScene)
window.rootViewController = UIHostingController(rootView: contentView)
self.window = window
window.makeKeyAndVisible()
}
}
func sceneDidDisconnect(_ scene: UIScene) {}
func sceneDidBecomeActive(_ scene: UIScene) {}
func sceneWillResignActive(_ scene: UIScene) {}
func sceneWillEnterForeground(_ scene: UIScene) {}
func sceneDidEnterBackground(_ scene: UIScene) {
(UIApplication.shared.delegate as? AppDelegate)?.saveContext()
}
}
AppDelegate（与模板不变，提供完整性）：
import UIKit
import CoreData
@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
return true
}
func application(_ application: UIApplication, configurationForConnecting connectingSceneSession: UISceneSession, options: UIScene.ConnectionOptions) -> UISceneConfiguration {
return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)
}
func application(_ application: UIApplication, didDiscardSceneSessions sceneSessions: Set<UISceneSession>) {}
// MARK: - Core Data stack
lazy var persistentContainer: NSPersistentCloudKitContainer = {
let container = NSPersistentCloudKitContainer(name: "Coredata134")
container.loadPersistentStores(completionHandler: { (storeDescription, error) in
if let error = error as NSError? {
fatalError("Unresolved error \(error), \(error.userInfo)")
}
})
return container
}()
func saveContext () {
let context = persistentContainer.viewContext
if context.hasChanges {
do {
try context.save()
} catch {
let nserror = error as NSError
fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
}
}
}
}
【问题讨论】：