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

面临的问题“类型为'AppDelegate'的值没有成员'managedObjectContext'在尝试在View Controller中创建新上下文时,在新的Xcode 8(使用Swift 3,iOS 10)中

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通过以下方式呈现:惰性varpersistentContainer:NSPersistentContainer属性和func saveContext()。 没有managedObjectContext属性。

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

Adelmaer asked 2020-06-16T22:35:38Z
5个解决方案
86 votes

在Swift3中,您可以通过viewContext访问managedObjectContext,如下所示:

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

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,请完成添加核心数据的正常过程,并添加以下代码,这将使您获得

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
}()

您将需要导入CoreData。

注意:对于Swift3,ManagedObject子类是自动生成的。从WWDC 2016了解更多

James Amo answered 2020-06-16T22:36:00Z
39 votes

将所有核心数据堆栈代码移至单个文件,并添加了iOS 10和iOS10以下版本。 以下是我的尝试(不确定其是否完全符合要求)

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()
            }
        }
    }
}
anoop4real answered 2020-06-16T22:36:20Z
28 votes

James Amo的解决方案为您提供了iOS 10.0的大部分解决方案,但无法解决iOS 9.0及更低版本的问题,因为它无法访问该方法,因此需要手动构建persistentContainer。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)")
        }

    }

显然,将10.0更改使CoreData显着简化了,但不幸的是,这对现有开发人员进行这种转换非常痛苦。

要实现上述目的,只需确保将persistentContainer放入您在James Amo的答案中定义的AppDelegate.swift中即可。

legel answered 2020-06-16T22:36:49Z
3 votes

managedObjectContext具有NSManagedObjectContext类型的viewContext属性。

附带说明一下,如果您在Xcode 8中创建一个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AppDelegate中的viewContext属性进行设置。

Kevin Low answered 2020-06-16T22:37:14Z
1 votes

首先,获取AppDelegate对象:

let appDelegateObject = UIApplication.shared.delegate as! AppDelegate

现在,我们可以将托管对象获取为:

let managedObject = appDelegateObject.persistentContainer.viewContext
Vivek Tyagi answered 2020-06-16T22:37:38Z
translate from https://stackoverflow.com:/questions/37956720/how-to-create-managedobjectcontext-using-swift-3-in-xcode-8