ios 10 和 ios 9 中的 NSManagedObjectContext（核心数据）

Question

我有一个使用支持 ios 9 和 ios 10 的核心数据的应用程序。我正在使用 xcode 8.2.1 来开发这个项目。 AppDelegate 文件具有在应用程序在 ios 10 上运行时获取 ManagedObjectContext 的方法，但是，当应用程序在 ios 9 上运行时我如何获取它。我尝试谷歌搜索但没有什么帮助。任何帮助！

我用来获取 ManagedObjectContext 的代码在这里：

 NSManagedObjectContext *context = ((AppDelegate*)[[UIApplication sharedApplication] delegate]).persistentContainer.viewContext;

Answer 1

如果您的应用同时支持 ios 9 和 ios 10，那么您可以使用 #available 属性来检查当前运行的版本并相应地运行代码，因为 NSPersistentContainer 仅适用于 iOS 10 及更高版本。

在 Swift 3 中

// MARK: - Core Data Saving support

    func saveContext () {

        let coreDataFileName = "Use your core data file name"

        if #available(iOS 10.0, *) {
            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)")
                }
            }
        }else {

            if managedObjectContext.hasChanges {
                do {
                    try managedObjectContext.save()
                } catch let error as NSError {
                    print("Ops there was an error \(error.localizedDescription)")
                    abort()
                }
            }

        }
    }

    // Applications default directory address
    lazy var applicationDocumentsDirectory: NSURL = {
        let urls = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
        return urls[urls.count-1] as NSURL
    }()
    lazy var managedObjectModel: NSManagedObjectModel = {
        // 1
        let modelURL = Bundle.main.url(forResource: coreDataFileName, withExtension: "momd")!
        return NSManagedObjectModel(contentsOf: modelURL)!
    }()
    lazy var persistentStoreCoordinator: NSPersistentStoreCoordinator = {
        let coordinator = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel)
        let url = self.applicationDocumentsDirectory.appendingPathComponent("\(coreDataFileName).sqlite")
        do {
            // If your looking for any kind of migration then here is the time to pass it to the options
            try coordinator.addPersistentStore(ofType: NSSQLiteStoreType, configurationName: nil, at: url, options: nil)
        } catch let  error as NSError {
            print("Ops there was an error \(error.localizedDescription)")
            abort()
        }
        return coordinator
    }()

    lazy var managedObjectContext: NSManagedObjectContext = {
        //    // Returns the managed object context for the application (which is already bound to the persistent store coordinator for the
        //    application.) This property is optional since there are legitimate error conditions that could cause the creation of the context to
        //    fail.
        let coordinator = self.persistentStoreCoordinator
        var context = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)
        context.persistentStoreCoordinator = coordinator
        return context
    }()

在目标中 - C 在 AppDelegate.m 中

#pragma mark - Core Data Saving support

@synthesize managedObjectContext = _managedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;
@synthesize persistentContainer = _persistentContainer;

- (NSURL *)applicationDocumentsDirectory {
    // The directory the application uses to store the Core Data store file. This code uses a directory named "Your Bundle Indentifier" in the application's documents directory.
    return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}

- (NSManagedObjectModel *)managedObjectModel {
    // The managed object model for the application. It is a fatal error for the application not to be able to find and load its model.
    if (_managedObjectModel != nil) {
        return _managedObjectModel;
    }
    NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Use your core data file name" withExtension:@"momd"];
    _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
    return _managedObjectModel;
}

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {
    // The persistent store coordinator for the application. This implementation creates and returns a coordinator, having added the store for the application to it.
    if (_persistentStoreCoordinator != nil) {
        return _persistentStoreCoordinator;
    }

    // Create the coordinator and store

    _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"Use your core data file name.sqlite"];
    NSError *error = nil;
    NSString *failureReason = @"There was an error creating or loading the application's saved data.";
    if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
        // Report any error we got.
        NSMutableDictionary *dict = [NSMutableDictionary dictionary];
        dict[NSLocalizedDescriptionKey] = @"Failed to initialize the application's saved data";
        dict[NSLocalizedFailureReasonErrorKey] = failureReason;
        dict[NSUnderlyingErrorKey] = error;
        error = [NSError errorWithDomain:@"YOUR_ERROR_DOMAIN" code:9999 userInfo:dict];
        // Replace this with code to handle the error appropriately.
        // abort() 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.
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }

    return _persistentStoreCoordinator;
}


- (NSManagedObjectContext *)managedObjectContext {
    // Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.)
    if (_managedObjectContext != nil) {
        return _managedObjectContext;
    }

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (!coordinator) {
        return nil;
    }
    _managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
    [_managedObjectContext setPersistentStoreCoordinator:coordinator];
    return _managedObjectContext;
}

#pragma mark - Core Data Saving support

- (void)saveContext {

    //Check current version.
    if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 10.0){

        NSManagedObjectContext *context =_persistentContainer.viewContext;

        if (context != nil) {
            NSError *error = nil;
            if ([context hasChanges] && ![context save:&error]) {
                // Replace this implementation with code to handle the error appropriately.
                // abort() 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.
                NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
                abort();
            }
        }
    }else{
        NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
        if (managedObjectContext != nil) {
            NSError *error = nil;
            if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
                // Replace this implementation with code to handle the error appropriately.
                // abort() 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.
                NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
                abort();
            }
        }
    }
}

在 AppDelegate.h 中使用

#pragma mark - Core data for messages vriable
@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;
@property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel;
@property (readonly, strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;
@property (readonly, strong) NSPersistentContainer *persistentContainer;

- (void)saveContext;
- (NSURL *)applicationDocumentsDirectory;

Answer 2

正如 Jon Rose 所说，NSPersistentContainer 仅适用于 iOS 10。 如果您仍然需要您的应用程序在以前的版本中运行，最好的解决方案是使用旧的 Core Data Stack，这里有一篇很棒的博客解释了这两种方法之间的区别：Core Data in ios10

另一种解决方案是在 swift 中使用#available 属性来执行核心数据堆栈或 NSPersistentContainer，这里有关于此的文档：Swift Attributes

Answer 3

NSPersistentContainer 仅适用于 iOS 10 及更高版本。如果您需要支持较低的系统，那么您将无法使用它。您必须在没有NSPersistentContainer 的情况下设置自己的核心数据堆栈。