如何在Xcode 8中使用Swift 3创建managedObjectContext？

Question

面对问题"值类型'AppDelegate'没有成员'managedObjectContext'在新的Xcode 8中(使用Swift 3,iOS 10)尝试在View Controller中创建新的上下文时

let context = (UIApplication.shared().delegate as! AppDelegate).managedObjectContext

在Xcode 8中,AppDelegate.swift文件中没有managedObjectContext的代码.AppDelegate.swift中的核心数据堆栈代码仅显示:lazy var persistentContainer:NSPersistentContainer属性和func saveContext().没有managedObjectContext属性.

如何在Xcode 8)中使用Swift 3创建managedObjectContext,或者可能没有必要使用Swift 3来创建它？

Answer 1

在Swift3中,您可以通过viewContext访问managedObjectContext

let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext

如果在创建项目时启用了Core数据,则此选项可用.但是,对于要包含核心数据的现有项目,请完成添加核心数据的正常过程并添加以下代码,以便您获取

lazy var persistentContainer: NSPersistentContainer = {

    let container = NSPersistentContainer(name: "you_model_file_name")
    container.loadPersistentStores(completionHandler: { (storeDescription, error) in
        if let error = error {

            fatalError("Unresolved error \(error), \(error.userInfo)")
        }
    })
    return container
}()

您需要导入CoreData.

注意:对于Swift3,将自动生成ManagedObject子类.从WWDC 2016了解更多信息

Answer 2

将所有核心数据堆栈代码移动到单个文件并添加iOS 10和iOS10以下.下面是我的尝试(不确定它完全达到标记)

import Foundation
import CoreData

class CoreDataManager {
    // MARK: - Core Data stack
    static let sharedInstance = CoreDataManager()

    private lazy var applicationDocumentsDirectory: URL = {
        // The directory the application uses to store the Core Data store file. This code uses a directory named in the application's documents Application Support directory.
        let urls = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
        return urls[urls.count-1]
    }()

    private lazy var managedObjectModel: NSManagedObjectModel = {
        // The managed object model for the application. This property is not optional. It is a fatal error for the application not to be able to find and load its model.
        let modelURL = Bundle.main.url(forResource: "CoreDataSwift", withExtension: "momd")!
        return NSManagedObjectModel(contentsOf: modelURL)!
    }()

    private lazy var persistentStoreCoordinator: NSPersistentStoreCoordinator = {
        // The persistent store coordinator for the application. This implementation creates and returns a coordinator, having added 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.
        // Create the coordinator and store
        let coordinator = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel)
        let url = self.applicationDocumentsDirectory.appendingPathComponent("CoreDataSwift.sqlite")
        var failureReason = "There was an error creating or loading the application's saved data."
        do {
            // Configure automatic migration.
            let options = [ NSMigratePersistentStoresAutomaticallyOption : true, NSInferMappingModelAutomaticallyOption : true ]
            try coordinator.addPersistentStore(ofType: NSSQLiteStoreType, configurationName: nil, at: url, options: options)
        } catch {
            // Report any error we got.
            var dict = [String: AnyObject]()
            dict[NSLocalizedDescriptionKey] = "Failed to initialize the application's saved data" as AnyObject?
            dict[NSLocalizedFailureReasonErrorKey] = failureReason as AnyObject?

            dict[NSUnderlyingErrorKey] = error as NSError
            let wrappedError = NSError(domain: "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 \(wrappedError), \(wrappedError.userInfo)")
            abort()
        }

        return coordinator
    }()

    lazy var managedObjectContext: NSManagedObjectContext = {

        var managedObjectContext: NSManagedObjectContext?
        if #available(iOS 10.0, *){

            managedObjectContext = self.persistentContainer.viewContext
        }
        else{
        // 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
        managedObjectContext = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)
        managedObjectContext?.persistentStoreCoordinator = coordinator

        }
        return managedObjectContext!
    }()
    // iOS-10
    @available(iOS 10.0, *)
    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: "CoreDataSwift")
        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)")
            }
        })
        print("\(self.applicationDocumentsDirectory)")
        return container
    }()
    // MARK: - Core Data Saving support

    func saveContext () {
        if managedObjectContext.hasChanges {
            do {
                try managedObjectContext.save()
            } catch {
                // 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.
                let nserror = error as NSError
                NSLog("Unresolved error \(nserror), \(nserror.userInfo)")
                abort()
            }
        }
    }
}

Answer 3

James Amo的解决方案可以为iOS 10.0提供大部分解决方案,但不能解决iOS 9.0及更低版本,它无法访问该方法并需要手动构建NSManagedObjectModel.这是适合我的解决方案:

    var context: NSManagedObjectContext?

    if #available(iOS 10.0, *) {
        context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
    } else {
        // iOS 9.0 and below - however you were previously handling it
        guard let modelURL = Bundle.main.url(forResource: "Model", withExtension:"momd") else {
            fatalError("Error loading model from bundle")
        }
        guard let mom = NSManagedObjectModel(contentsOf: modelURL) else {
            fatalError("Error initializing mom from: \(modelURL)")
        }
        let psc = NSPersistentStoreCoordinator(managedObjectModel: mom)
        context = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)
        let urls = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
        let docURL = urls[urls.endIndex-1]
        let storeURL = docURL.appendingPathComponent("Model.sqlite")
        do {
            try psc.addPersistentStore(ofType: NSSQLiteStoreType, configurationName: nil, at: storeURL, options: nil)
        } catch {
            fatalError("Error migrating store: \(error)")
        }

    }

很明显,对10.0的更改使CoreData变得更加简单,但不幸的是现有开发人员如此痛苦地跳起来......

要实现上述功能,只需确保将其persistentContainer放入James Amo的答案中定义的AppDelegate.swift中.