let fetchedResultsController: NSFetchedResultsController = ...
var error : NSError?
fetchedResultsController.performFetch(&error)
if let error = error {
    NSLog("Error: \(error)")
}
let lists: [List] = fetchedResultsController.fetchedObjects! as [List]
NSLog("lists count = \(lists.count)")
for list: List in lists {
    NSLog("List: \(list.description)")
}

它的工作方式与预期的一样,我将List对象描述打印到控制台.
我想为我的应用程序编写一些单元测试,所以我创建了扩展XCTestCase的类.代码编译没有问题,测试运行,但不幸的是我无法在该上下文中获取List对象.

我在控制台中获得的所有内容都是List对象的数量和致命错误：

lists count = 59
fatal error: NSArray element Failed to match the Swift Array Element type

线路上升：

for list: List in lists {

我很确定我已经正确配置了目标,因为我可以创建List对象并将其插入到托管对象上下文中,而不会出现我的应用程序源代码以及单元测试源代码的问题.我遇到的唯一问题是从测试单元获取.我想知道为什么在模拟器中运行应用程序时提取工作正常,并且在单元测试期间执行时失败.

任何可能出错的想法都将受到赞赏.

更新：

更具体地说,我的实现如何,这里是我正在玩的完整代码示例：

var error: NSError? = nil

let urls = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory,inDomains: .UserDomainMask)
let applicationDocumentsDirectory = urls[urls.count-1] as NSURL

let modelURL = NSBundle.mainBundle().URLForResource("CheckLists",withExtension: "momd")!
let managedObjectModel = NSManagedObjectModel(contentsOfURL: modelURL)

var coordinator: NSPersistentStoreCoordinator? = NSPersistentStoreCoordinator(managedObjectModel: managedObjectModel)
let url = applicationDocumentsDirectory.URLByAppendingPathComponent("CheckLists.sqlite")
if coordinator!.addPersistentStoreWithType(NSsqliteStoreType,configuration: nil,URL: url,options: nil,error: &error) == nil {
    NSLog("Error1: \(error)")
    abort()
}

var managedObjectContext = NSManagedObjectContext()
managedObjectContext.persistentStoreCoordinator = coordinator

let fetchRequest = NSFetchRequest()
fetchRequest.entity = NSEntityDescription.entityForName("List",inManagedObjectContext: managedObjectContext)
fetchRequest.sortDescriptors = [ NSSortDescriptor(key: "name",ascending: true) ]

let fetchedResultsController = NSFetchedResultsController(
    fetchRequest: fetchRequest,managedObjectContext: managedObjectContext,sectionNameKeyPath: nil,cacheName: "ListFetchedResultsControllerCache"
)

fetchedResultsController.performFetch(&error)
if let error = error {
    NSLog("Error2: \(error)")
    abort()
}

let fetchedObjects: [AnyObject]? = fetchedResultsController.fetchedObjects
if let fetchedObjects = fetchedObjects {
    NSLog("Fetched objects count: \(fetchedObjects.count)")
    for fetchedObject in fetchedObjects {
        NSLog("Fetched object: \(fetchedObject.description)")
    }
}
else {
    NSLog("Fetched objects array is nil")
}

let fetchedLists: [List]? = fetchedResultsController.fetchedObjects as? [List]
if let fetchedLists = fetchedLists {
    NSLog("Fetched lists count: \(fetchedLists.count)")
    for fetchedList in fetchedLists {
        NSLog("Fetched list: \(fetchedList.description)")
    }
}
else {
    NSLog("Fetched lists array is nil")
}

当我从应用程序的源代码执行它,在模拟器中运行应用程序时,控制台输出如下所示：

Fetched objects count: 3
Fetched object: <CheckLists.List: 0x7a6866f0> (entity: List; id: 0x7a686020 <x-coredata://7A87B5BE-C2FA-4150-B9E3-879FDE07F0B9/List/p2> ; data: {
    name = "List 1";
})
Fetched object: <CheckLists.List: 0x7a686930> (entity: List; id: 0x7a686030 <x-coredata://7A87B5BE-C2FA-4150-B9E3-879FDE07F0B9/List/p1> ; data: {
    name = "List 2";
})
Fetched object: <CheckLists.List: 0x7a686970> (entity: List; id: 0x7a686040 <x-coredata://7A87B5BE-C2FA-4150-B9E3-879FDE07F0B9/List/p3> ; data: {
    name = "List 3";
})
Fetched lists count: 3
Fetched list: <CheckLists.List: 0x7a6866f0> (entity: List; id: 0x7a686020 <x-coredata://7A87B5BE-C2FA-4150-B9E3-879FDE07F0B9/List/p2> ; data: {
    name = "List 1";
})
Fetched list: <CheckLists.List: 0x7a686930> (entity: List; id: 0x7a686030 <x-coredata://7A87B5BE-C2FA-4150-B9E3-879FDE07F0B9/List/p1> ; data: {
    name = "List 2";
})
Fetched list: <CheckLists.List: 0x7a686970> (entity: List; id: 0x7a686040 <x-coredata://7A87B5BE-C2FA-4150-B9E3-879FDE07F0B9/List/p3> ; data: {
    name = "List 3";
})

但是,当我从单元测试中执行此代码时,我得到此输出：

Fetched objects count: 3
Fetched object: <CheckLists.List: 0x7a07df50> (entity: List; id: 0x7a07d7e0 <x-coredata://7A87B5BE-C2FA-4150-B9E3-879FDE07F0B9/List/p2> ; data: {
    name = "List 1";
})
Fetched object: <CheckLists.List: 0x7a07e190> (entity: List; id: 0x7a07d7f0 <x-coredata://7A87B5BE-C2FA-4150-B9E3-879FDE07F0B9/List/p1> ; data: {
    name = "List 2";
})
Fetched object: <CheckLists.List: 0x7a07e1d0> (entity: List; id: 0x7a07d800 <x-coredata://7A87B5BE-C2FA-4150-B9E3-879FDE07F0B9/List/p3> ; data: {
    name = "List 3";
})
Fetched lists array is nil

我希望它更容易理解问题所在.不知何故,这句话：

let fetchedLists: [List]? = fetchedResultsController.fetchedObjects as? [List]

当app在模拟器中运行时,会生成一个List对象数组,但是当从单元测试执行时,它无法生成nil.