ios - 传递 NSManagedObjectContext 的实例

Question

我使用 MagicalRecord使用核心数据。

我有一个名为 DatabaseManager 的单独类来处理与核心数据相关的任务。我有一个接受 NSManagedObjectContext 对象的初始化程序。

import CoreData
import Foundation
import MagicalRecord
import SwiftyJSON

public class DatabaseManager {

    private let context: NSManagedObjectContext!

    init(context: NSManagedObjectContext) {
        self.context = context
    }

    public func insertReports(data: AnyObject, success: () -> Void, failure: (error: NSError?) -> Void) {
        MagicalRecord.cleanUp()
        MagicalRecord.setupCoreDataStackWithStoreNamed("Records")

        let json = JSON(data)
        if let reports = json.array {
            for reportObj in reports {
                let report = Report.MR_createInContext(context) as Report
                report.id = reportObj["Id"].int
                report.type = reportObj["Type"].string!
            }
            context.MR_saveToPersistentStoreAndWait()
            success()
        }
    }

    private func getReport(id: Int) -> Report {
        let idFilter = NSPredicate(format: "id == %@", NSNumber(integer: id))
        let fetchRequest = Report.MR_requestAllWithPredicate(idFilter, inContext: context)
        return Report.MR_executeFetchRequestAndReturnFirstObject(fetchRequest, inContext: context) as Report
    }
}

然后我初始化该类并调用它的 insertReports() 方法将一些记录插入到核心数据中。

let context = NSManagedObjectContext.MR_defaultContext()
let dbManager = DatabaseManager(context: context)

getReportsFromAPI({ (data) -> Void in
    dbManager.insertReports(data, success: { () -> Void in
        println("Reports added successfully")
    }, failure: { (error) -> Void in
        println("Error inserting Reports: \(error?.localizedDescription)")
    })
}, failure: { (error) -> Void in
    println("Error getting Reports from API: \(error?.localizedDescription)")
})

但这似乎行不通。我在控制台中得到以下输出。

2015-03-05 00:39:39.412 Reports[7123:967179] +[NSManagedObjectContext(MagicalRecord) MR_setDefaultContext:](0x104396400) Set Default Context: (null)
2015-03-05 00:39:39.412 Reports[7123:967179] +[NSManagedObjectContext(MagicalRecord) MR_setRootSavingContext:](0x104396400) Set Root Saving Context: (null)
2015-03-05 00:39:39.583 Reports[7123:967179] +[NSManagedObjectContext(MagicalRecord) MR_contextWithStoreCoordinator:](0x104396400) -> Created Context UNNAMED
2015-03-05 00:39:39.584 Reports[7123:967179] +[NSManagedObjectContext(MagicalRecord) MR_setRootSavingContext:](0x104396400) Set Root Saving Context: <NSManagedObjectContext: 0x7f81b04c6b00>
2015-03-05 00:39:39.584 Reports[7123:967179] +[NSManagedObjectContext(MagicalRecord) MR_newMainQueueContext](0x104396400) Created Main Queue Context: <NSManagedObjectContext: 0x7f81b04c75a0>
2015-03-05 00:39:39.584 Reports[7123:967179] +[NSManagedObjectContext(MagicalRecord) MR_setDefaultContext:](0x104396400) Set Default Context: <NSManagedObjectContext: 0x7f81b04c75a0>
2015-03-05 00:39:40.434 Reports[7123:967179] +[NSManagedObjectContext(MagicalRecord) MR_setDefaultContext:](0x104396400) Set Default Context: (null)
2015-03-05 00:39:40.434 Reports[7123:967179] +[NSManagedObjectContext(MagicalRecord) MR_setRootSavingContext:](0x104396400) Set Root Saving Context: (null)
2015-03-05 00:39:40.435 Reports[7123:967179] +[NSManagedObjectContext(MagicalRecord) MR_setDefaultContext:](0x104396400) Set Default Context: (null)
2015-03-05 00:39:40.435 Reports[7123:967179] +[NSManagedObjectContext(MagicalRecord) MR_setRootSavingContext:](0x104396400) Set Root Saving Context: (null)
2015-03-05 00:39:40.443 Reports[7123:967179] +[NSManagedObjectContext(MagicalRecord) MR_contextWithStoreCoordinator:](0x104396400) -> Created Context UNNAMED
2015-03-05 00:39:40.443 Reports[7123:967179] +[NSManagedObjectContext(MagicalRecord) MR_setRootSavingContext:](0x104396400) Set Root Saving Context: <NSManagedObjectContext: 0x7f81b280e5a0>
2015-03-05 00:39:40.444 Reports[7123:967179] +[NSManagedObjectContext(MagicalRecord) MR_newMainQueueContext](0x104396400) Created Main Queue Context: <NSManagedObjectContext: 0x7f81b04d76c0>
2015-03-05 00:39:40.444 Reports[7123:967179] +[NSManagedObjectContext(MagicalRecord) MR_setDefaultContext:](0x104396400) Set Default Context: <NSManagedObjectContext: 0x7f81b04d76c0>
2015-03-05 00:39:40.446 Reports[7123:967179] -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x7f81b04c75a0) → Saving <NSManagedObjectContext (0x7f81b04c75a0): *** DEFAULT ***> on *** MAIN THREAD ***
2015-03-05 00:39:40.446 Reports[7123:967179] -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x7f81b04c75a0) → Save Parents? 1
2015-03-05 00:39:40.447 Reports[7123:967179] -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x7f81b04c75a0) → Save Synchronously? 1
2015-03-05 00:39:40.448 Reports[7123:967179] -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x7f81b04c6b00) → Saving <NSManagedObjectContext (0x7f81b04c6b00): *** BACKGROUND SAVING (ROOT) ***> on *** MAIN THREAD ***
2015-03-05 00:39:40.448 Reports[7123:967179] -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x7f81b04c6b00) → Save Parents? 1
2015-03-05 00:39:40.448 Reports[7123:967179] -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x7f81b04c6b00) → Save Synchronously? 1

在那之后，它就卡住了。没有抛出错误，但保存操作也没有完成。

我用 NSManagedObjectContext.MR_defaultContext() 替换了我使用属性上下文的地方，然后运行应用程序，数据成功保存。

为什么我不能通过初始化器传入 MR_defaultContext() 的实例？

Answer 1

您的回溯说明了一切，您设置了太多与持久存储的连接。魔法唱片 documentation详细说明您应该在 App Delegate 的 didFinishLaunching 阶段，或者在您的情况下，在实例化 DatabaseManager 类时设置您的堆栈。

因此对 MagicalRecord.setupCoreDataStackWithStoreNamed("Records") 的调用应该转移到您的初始化程序(将其放在 dispatch_once block 中可能更安全，以防止它被设置多次)

init(context: NSManagedObjectContext) {
    struct Static {
        static var onceToken : dispatch_once_t = 0
    }
    dispatch_once(&(Static.onceToken)) {
        MagicalRecord.setupCoreDataStackWithStoreNamed("Records")
    }
    self.context = context
}

顺便说一句，你只需要在你的应用程序关闭时调用清理，所以也许在你的 App Delegate 的 willTerminate

MagicalRecord 一切顺利 :)