ios 如何在 Xcode 8 中使用 Swift 3 创建 managedObjectContext？

How to create managedObjectContext using Swift 3 in Xcode 8?

提问by Adelmaer

Facing issue "Value of type 'AppDelegate' has no member 'managedObjectContext' In new Xcode 8 (using Swift 3, iOS 10) when trying to create new context in View Controller

在新的 Xcode 8（使用 Swift 3、iOS 10）中尝试在视图控制器中创建新上下文时，面临问题“类型‘AppDelegate’的值没有成员‘managedObjectContext’

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

In Xcode 8 there is no code for managedObjectContext inside AppDelegate.swift file. Core Data stack code inside AppDelegate.swift presented only with: lazy var persistentContainer: NSPersistentContainer property and func saveContext () . There is no managedObjectContext property.

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提供：lazy var persistentContainer: NSPersistentContainer 属性和 func saveContext () 。没有 managedObjectContext 属性。

How to create managedObjectContext using Swift 3 in Xcode 8) or maybe there is no need to do it using Swift 3 ?

如何在 Xcode 8 中使用 Swift 3 创建 managedObjectContext 或者也许不需要使用 Swift 3 来创建？

回答by James Amo

In Swift3, you can access the managedObjectContext via the viewContext as

在 Swift3 中，您可以通过 viewContext 访问 managedObjectContext 作为

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

This option is available if Core data was enabled when creating the project. However, for existing project that you want to include core data, go through the normal process of adding the core data and add the following code which will allow you to get the

如果在创建项目时启用了核心数据，则此选项可用。但是，对于要包含核心数据的现有项目，请执行添加核心数据的正常过程并添加以下代码，这将允许您获得

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
}()

You will need to import the CoreData.

您将需要导入 CoreData。

Note: For Swift3, the ManagedObject Subclass are generated automatically. See more from WWDC 2016

注意：对于 Swift3，ManagedObject 子类是自动生成的。查看更多来自 WWDC 2016

回答by anoop4real

Moved all the core data stack code to a single file and added iOS 10 and below iOS10. below is my try (not sure its fully up to the mark)

将所有核心数据堆栈代码移至单个文件，并添加了 iOS 10 及 iOS10 以下版本。下面是我的尝试（不确定它是否完全符合标准）

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()
            }
        }
    }
}

回答by legel

The solution by James Amogets you most of the way there for iOS 10.0, but doesn't address iOS 9.0 and below, which can't access that method and needs to manually build the NSManagedObjectModel. Here is the solution that worked for me:

James Amo的解决方案为您提供了适用于 iOS 10.0 的大部分方法，但没有解决无法访问该方法并需要手动构建NSManagedObjectModel. 这是对我有用的解决方案：

    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)")
        }

    }

It's clear that the change to 10.0 makes CoreData significantly simpler, but it's unfortunate that it's so painful for existing developers to make the jump...

很明显，对 10.0 的更改使 CoreData 显着更简单，但不幸的是，现有开发人员进行跳跃如此痛苦......

To implement the above, just make sure to throw the persistentContainerinto your AppDelegate.swift, defined in James Amo's answer.

要实现上述内容，只需确保将persistentContainer放入您的 AppDelegate.swift 中，在James Amo的回答中定义。

回答by Kevin Low

NSPersistentContainerhas a viewContextproperty that is an NSManagedObjectContexttype.

NSPersistentContainer有一个类型的viewContext属性NSManagedObjectContext。

As a side note, if you create a Master-Detail application in Xcode 8, Apple's sample code puts the managedObjectContextproperty in the MasterViewController.swift file and sets it by using said viewContextproperty in AppDelegate.

附带说明一下，如果您在 Xcode 8 中创建 Master-Detail 应用程序，Apple 的示例代码会将managedObjectContext属性放在 MasterViewController.swift 文件中，并使用viewContextAppDelegate 中的所述属性进行设置。

回答by Vivek Tyagi

First, get AppDelegate object:-

首先，获取 AppDelegate 对象：-

let appDelegateObject = UIApplication.shared.delegate as! AppDelegate

And now, we can get managed object as:

现在，我们可以将托管对象获取为：

let managedObject = appDelegateObject.persistentContainer.viewContext