＆lt; <error type =“”>＆gt;为NSManagedObject返回</error>

Question

我有一个NSFetchRequest，它返回多个名为＆＃34; Duty＆＃34;的NSManagedObjects。 如果成功则返回类似[Duty]的数组。 我想对数组进行枚举，并对每个职责做一些事情。这是在for循环中完成的。我的问题是循环中的任务返回为<<error type>>，如下所示：

但是，如果我通过数组中的索引直接访问一个任务，那么结果很好，如下所示：

//Find duties for calendar export
        var dutiesRequest = NSFetchRequest()
        dutiesRequest.entity = NSEntityDescription.entityForName("Duty", inManagedObjectContext: managedObjectContext)

        dutiesRequest.sortDescriptors = [NSSortDescriptor(key: "startDate", ascending: true)]
        dutiesRequest.predicate = NSPredicate(format: "(startDate >= %@) AND (startDate <= %@)", fromDate, toDate)

        var dutiesFetchError : NSError?

        let duties = managedObjectContext.executeFetchRequest(dutiesRequest, error: &dutiesFetchError) as [Duty]

        //If I get the duty by its index it works:
        let duty = duties[0] as Duty

有人能发现原因吗？我的代码是错误的还是这可能是XCode中的错误？

感谢您的时间！

修改

对不起，我应该包含所有代码，因为当我删除一些早期的代码时问题就消失了。 我想确保操作不在主线程上执行，所以我调用了另一个线程，如下所示：

class func saveToCalendarInBackground(eventStore:EKEventStore, calendar:EKCalendar, fromDate: NSDate, toDate: NSDate, previousEventIDs: [String:String], managedObjectContext: NSManagedObjectContext, progress: (progress: Float!) -> (), completion:(newEventIDs: [String:String]!, error: NSError!) -> ()) -> Void {

    //Run the operations on another thread (not main), but move the progress and completion closures to the main thread with GCD
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {

        //Find duties for calendar import
        var dutiesRequest = NSFetchRequest()
        dutiesRequest.entity = NSEntityDescription.entityForName("Duty", inManagedObjectContext: managedObjectContext)

        dutiesRequest.sortDescriptors = [NSSortDescriptor(key: "startDate", ascending: true)]
        dutiesRequest.predicate = NSPredicate(format: "(startDate >= %@) AND (startDate <= %@)", fromDate, toDate)

        var dutiesFetchError : NSError?

        let duties = managedObjectContext.executeFetchRequest(dutiesRequest, error: &dutiesFetchError) as [Duty]

        //If I get the duty by its index it works:
        //let duty = duties[0] as Duty

        if dutiesFetchError == nil {

            for duty in duties {

            }
        }
        else {
            //Return callbacks on main thread
            dispatch_async(dispatch_get_main_queue(), {

                completion(newEventIDs: nil, error: NSError(domain: "CalendarManagerDomain", code: 0, userInfo: [NSLocalizedFailureReasonErrorKey : "Found no duties for calendar export."]))

            })
        }
    })
}

如果我删除

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), { })

for循环正确地找到每个职责。

对此有何解释？