使用 NSFetchedResultsController 对描述符进行排序 - Swift

Question

我有一个 UITableView 来自 Core Data 和一个 NSFetchedResultsController 返回位置实体。默认排序（和节标题）是通过实体名称的第一个字母。这行得通（尽管我仍在尝试将大写和小写正确地组合到同一部分中。）用户可以选择按三个可选类别之一（它们是实体的属性）对表格进行排序，然后对这些类别进行排序按实体名称。

当我设置为按类别排序时，出现以下运行时错误：

[_TtCSs23_ContiguousArrayStorage00007F80513B59D0 key]: unrecognized selector sent to instance 0x7f80513b5720

这是我的NSFetchedResultsController：

var sectionNameKeyPathString1: String?
var sectionNameKeyPathString2: String?

var fetchedResultsController: NSFetchedResultsController {
    if _fetchedResultsController != nil {
        return _fetchedResultsController!
    }

    let fetchRequest = NSFetchRequest()
    // Edit the entity name as appropriate.
    let entity = NSEntityDescription.entityForName("Location", inManagedObjectContext: self.managedObjectContext!)
    fetchRequest.entity = entity

    // Set the batch size to a suitable number.
    fetchRequest.fetchBatchSize = 20

    // Edit the sort key as appropriate.
    if sectionNameKeyPathString1 != nil {
        let sortDescriptor1 = NSSortDescriptor(key: sectionNameKeyPathString1!, ascending: true)
        let sortDescriptor2 = NSSortDescriptor(key: sectionNameKeyPathString2!, ascending: true)
        let sortDescriptors = [sortDescriptor1, sortDescriptor2]
        fetchRequest.sortDescriptors = [sortDescriptors]
    } else {
        let sortDescriptor = NSSortDescriptor(key: "locationName", ascending: true)
        fetchRequest.sortDescriptors = [sortDescriptor]
    }

    var sectionNameKeyPath: String
    if sectionNameKeyPathString1 == nil {
        sectionNameKeyPath = "firstLetterAsCap"
    } else {
        sectionNameKeyPath = sectionNameKeyPathString1!
    }

    // Edit the section name key path and cache name if appropriate.
    // nil for section name key path means "no sections".
    let aFetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: self.managedObjectContext!, sectionNameKeyPath: sectionNameKeyPath, cacheName: "Locations")
    aFetchedResultsController.delegate = self
    _fetchedResultsController = aFetchedResultsController

    var error: NSError? = nil
    if !_fetchedResultsController!.performFetch(&error) {
        // TODO: Handle this error
        // Replace this implementation 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.
        //println("Unresolved error \(error), \(error.userInfo)")
        abort()
    }

    return _fetchedResultsController!
}

使用断点我确信，例如 sectionNameKeyPathString1 = "category1" 和 sectionNameKeyPathString2 = "locationName" 以及 sectionNameKeyPath = "category1" 所以关键路径匹配第一个排序描述符。

我曾在 Obj-C 中进行过这项工作，但现在我正在拔头发，并确定我患有 bug 失明。

Answer 1

是不是你的 [] 太多了？

    let sortDescriptors = [sortDescriptor1, sortDescriptor2] // <- an [NSSortDescriptor]
    fetchRequest.sortDescriptors = [sortDescriptors] // <- now an [[NSSortDescriptor]]

应该是：

    fetchRequest.sortDescriptors = [sortDescriptor1, sortDescriptor2]