实例化 NSFetchedResultsController 以未捕获的异常终止

Question

我正在用抽象 class 的 fetchRequest 实例化 NSFetchedResultsController：

private func setupFetchController() {
    let fetchRequest : NSFetchRequest<NSFetchRequestResult> = SearchEntity.fetchRequest()
    let fetchController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
    self.fetchController = fetchController
}

SearchEntity 是 Person 和 Group 的抽象父 class。我用它来获取 2 个实体和 1 NSFetchedResultsController。但是，调用此函数时应用程序崩溃：

libc++abi.dylib: terminating with uncaught exception of type NSException

我已将范围缩小到取消注释和注释 NSFetchedResultsController 的创建。我还有 2 个功能完全相同的功能。

我 doing/is 哪里出错了？

编辑：添加到这里。我可以通过使用 context.performFetch(...) 手动获取 SearchEntity，这给了我正确的结果。但是，因此得名，我要搜索它，所以我需要能够有效地更新。

编辑2：

在其他地方运行的相同功能的示例：

private func setupFetchController() {
    let fetchRequest : NSFetchRequest<NSFetchRequestResult> = Person.fetchRequest()

    // Sort Persons
    let sortDescriptor = NSSortDescriptor(key: "firstName", ascending: true)
    let sortDescriptor2 = NSSortDescriptor(key: "lastName", ascending: true)
    fetchRequest.sortDescriptors = [sortDescriptor, sortDescriptor2]

    // Filter Persons (only iType = 1)
    let predicate = NSPredicate(format: "iType == %i", 1)
    fetchRequest.predicate = predicate

    // Create the FetchController
    let fetchController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: context, sectionNameKeyPath: "sectionName", cacheName: nil)
    self.fetchController = fetchController
}

Answer 1

您得到异常是因为至少需要一个排序描述符。

来自documentation：

You typically create an instance of NSFetchedResultsController as an instance variable of a table view controller. When you initialize the fetch results controller, you provide four parameters:

1) A fetch request. This must contain at least one sort descriptor to order the results.

2) A managed object context. The controller uses this context to execute the fetch request.

3) Optionally, a key path on result objects that returns the section name. The controller uses the key path to split the results into sections (passing nil indicates that the controller should generate a single section).

4) Optionally, the name of the cache file the controller should use (passing nil prevents caching). Using a cache can avoid the overhead of computing the section and index information.

实例化 NSFetchedResultsController 以未捕获的异常终止

Instantiating NSFetchedResultsController terminating with uncaught exception

swift

core-data

nsfetchedresultscontroller