ios - Swift 中的 NSFetchedResultsController 计数

Question

我是一名 Swift 开发新手，有 Objective-C 背景。

我有以下代码:

class KPCoreDataResultsController: NSObject, NSFetchedResultsControllerDelegate {

    var fetchedResultsController: NSFetchedResultsController

    let managedObjectContext = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext!

    let entityName: NSString
    var delegate: KPCoreDataResultsDelegate?

    var predicate: NSPredicate {
        get {
            return fetchedResultsController.fetchRequest.predicate!
        }
        set {
            fetchedResultsController.fetchRequest.predicate = newValue            
            do {
                try fetchedResultsController.performFetch()
            } catch {
                print(error)
            }
        }
    }
    var sortDescriptor: NSSortDescriptor!
    var count: NSInteger {
        return (fetchedResultsController.sections!.first!).numberOfObjects
    }

    init(entityName: String, predicate: NSPredicate, sortDescriptor: NSSortDescriptor) {
        self.entityName = entityName
        let fetchRequest = NSFetchRequest(entityName: entityName)
        fetchRequest.predicate = predicate
        fetchRequest.sortDescriptors = [sortDescriptor]
        fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: managedObjectContext, sectionNameKeyPath: nil, cacheName: nil)
        super.init()
    }
}

在自定义 Core Data Results Controller 文件中，以简化对 CoreData 内容的访问。当我从 TableView (numberOfRowsInSection) 调用结果 Controller 的计数属性时，应用程序崩溃并显示:

fatal error: unexpectedly found nil while unwrapping an Optional value

这是 TableView 代码:

override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return accountController.count
}

基本上，上面的代码给出了这个错误——我使用的 ! 错了吗？或者这里发生了什么？

Answer 1

尝试类似的东西

  return fetchedResultsController.sections![section].numberOfObjects