Question

我在App groups的两个应用之间共享了相同的.sqilte。

当我在App A中添加录音并打开App B（首次启动）时，应用B正确检索数据。

我想在App A和app B（已经在backrgound中启动）中添加录音时同步数据，app B可以在它回到前台时检索数据。

这就是为什么当App B重新回到前台时，我将Core Data Sack更新为applicationWillEnterForeground。哪种方法是正确的？

let directory = NSFileManager.defaultManager().containerURLForSecurityApplicationGroupIdentifier("group.com.sl.sharedData");

        let url = directory?.URLByAppendingPathComponent("sharedData.sqlite")
        let store = self.persistentStoreCoordinator?.persistentStoreForURL(url!)
        var error : NSError?
        if false == self.persistentStoreCoordinator?.removePersistentStore(store!, error: &error)
        {
            println("error = \(error!.localizedDescription)")
            return
        }
        let options = [
            NSMigratePersistentStoresAutomaticallyOption: true,
            NSInferMappingModelAutomaticallyOption: true,
            // Adding the journalling mode recommended by apple
            NSSQLitePragmasOption: ["journal_mode": "DELETE"]
        ]
        var failureReason = "There was an error creating or loading the application's saved data."
        if self.persistentStoreCoordinator?.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: url, options: options, error: &error) == nil {
            // Report any error we got.
            var dict = [String: AnyObject]()
            dict[NSLocalizedDescriptionKey] = "Failed to initialize the application's saved data"
            dict[NSLocalizedFailureReasonErrorKey] = failureReason
            dict[NSUnderlyingErrorKey] = error
            error = 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 \(error), \(error!.userInfo)")
            abort()
        }
        _persistentStoreCoordinator = nil
        _managedObjectContext = nil
        let rootViewController = self.window!.rootViewController as ViewController
        rootViewController.context = self.managedObjectContext

不幸的是，它不能按我的意愿运作。每次进入applicationWillEnterForeground时，都会复制检索到的数据。哪种方法是正确的？

//编辑2014/04/17：尝试使用Mundi的解决方案

我尝试了NSManagedObjectContextObjectsDidChangeNotification

   func applicationWillEnterForeground(application: UIApplication) {

        NSNotificationCenter.defaultCenter().addObserver(
            self,
            selector: "mergeContextChangesForNotification:",
            name: NSManagedObjectContextObjectsDidChangeNotification,
            object: managedObjectContext)

        let rootViewController = self.window!.rootViewController as ViewController
        rootViewController.context = managedObjectContext
        }
    }

func mergeContextChangesForNotification(notification : NSNotification){
        let otherContext: NSManagedObjectContext = notification.object as NSManagedObjectContext

        if((otherContext != managedObjectContext) && (otherContext.persistentStoreCoordinator == managedObjectContext.persistentStoreCoordinator)){

            managedObjectContext.performBlockAndWait{ () -> Void in

                self.managedObjectContext.mergeChangesFromContextDidSaveNotification(notification)
            }
        }
    }

mergeContextChangesForNotification已被调用，但我从未进入过这种情况：if otherContext != managedObjectContext) && (otherContext.persistentStoreCoordinator == managedObjectContext.persistentStoreCoordinator

Answer 1

如果应用已处于活动状态，则不应再次设置持久性商店协调员。 Xcode模板中使用的标准延迟初始化是充分且优选的。

相反，您可能希望收听NSManagedObjectContextObjectsDidChangeNotification并根据需要更新您的用户界面。

将Core Data Stack更新到applicationWillEnterForeground

1 个答案: