NSFetchedResultsController-未调用任何委托函数

Question

我一直在Stack上下寻找答案，但这似乎找不到任何可行的方法。问题很简单-我有一个View Controller，它有一个子Table View Controller。

class ViewController: UIView Controller { 
    var child: UIViewController!
    var managedObjectContext: NSManagedObjectContext! 

    init(context: NSManagedObjectContext) { 
        self.managedObjectContext = context
    }

    viewDidLoad() { 
    self.child = CustomTVC(context: self.managedObjectContext)
    self.child?.view.frame = SomeFrameThatFits
    self.addChild(child!)
    self.addSubview(child!.view)

   //Targeting
   self.someButton.addTarget(self, action: #selector(addHello()), for: .touchUpInside)
   }

   @objc func addHello() { 
    _ = CoreDataWriter(context: self.managedObjectContext).save()
   }
}

很棒，很棒，整洁，做得很好。我正在使用提供的ViewController在SceneDelegate中创建context类。

SceneDelegate

...

        let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext

if let windowScene = scene as? UIWindowScene {
            let window = UIWindow(windowScene: windowScene)
                window.rootViewController = ViewController(context: context)
            self.window = window
            window.makeKeyAndVisible()
}

现在，在我的ViewController类中，有一个按钮sendButton。所有这些按钮都可以使用下面编写的单独的CoreDataWriter类向我的CoreData添加另一个项目。

class CoreDataWriter { 
init(context: NSManagedObjectContext) {
    self.managedObjectContext = context
}

func save() {
   let message = Message(context: managedObjectContext)
   message.text = "Hello World!"

     do {
            try self.managedObjectContext.save()
            return nil
       } catch let error {
            print(error.localizedDescription)
       }
    }
}

现在，我已经literally copy and pasted Apple's example code进入了Table View Controller类：

   class CustomTVC: UITableViewController, NSFetchedResultsControllerDelegate {
    var managedObjectContext: NSManagedObjectContext!
    var fetchedResultsController: NSFetchedResultsController<Message>!

    init(context: NSManagedObjectContext) {
        self.managedObjectContext = context
        super.init(nibName: nil, bundle: nil)
    }

    override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) {
        super.init(nibName: nil, bundle: nil)
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        self.tableView.register(UITableViewCell.self, forCellReuseIdentifier: "default")
         initializeFetchedResultsController()
    }


    //MARK: CoreData connections
    func initializeFetchedResultsController() {
        let request = NSFetchRequest<Message>(entityName: "Message")
        let sort = NSSortDescriptor(key: "sent", ascending: true)
        let predicate = NSPredicate(format: "chat.id == %@", "123454")


        fetchedResultsController = NSFetchedResultsController(fetchRequest: request, managedObjectContext: self.managedObjectContext, sectionNameKeyPath: "chat.id", cacheName: "rootCache")
        fetchedResultsController.delegate = self

        do {
            try fetchedResultsController.performFetch()
        } catch {
            fatalError("Failed to initialize FetchedResultsController: \(error)")
        }
    }

    // MARK: - Table view data source

  override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "default", for: indexPath)
        // Set up the cell
        guard let object = self.fetchedResultsController?.object(at: indexPath) else {
            fatalError("Attempt to configure cell without a managed object")
        }
        //Populate the cell from the object
        cell.textLabel?.text = object.text
        return cell
    }

    override func numberOfSections(in tableView: UITableView) -> Int {
        return 1
    }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
         guard let sections = fetchedResultsController.sections else {
                   fatalError("No sections in fetchedResultsController")
               }
               let sectionInfo = sections[section]
               return sectionInfo.numberOfObjects
    }

    //MARK: More stuff for NSData

    func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        print("controller will change content")
        tableView.beginUpdates()
    }

    func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange sectionInfo: NSFetchedResultsSectionInfo, atSectionIndex sectionIndex: Int, for type: NSFetchedResultsChangeType) {
        print("in ctronoller")
        switch type {
        case .insert:
            tableView.insertSections(IndexSet(integer: sectionIndex), with: .fade)
        case .delete:
            tableView.deleteSections(IndexSet(integer: sectionIndex), with: .fade)
        case .move:
            break
        case .update:
            break
        @unknown default:
            fatalError()
        }
    }

    func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
        print("in didChange controller")
        switch type {
        case .insert:
            tableView.insertRows(at: [newIndexPath!], with: .fade)
        case .delete:
            tableView.deleteRows(at: [indexPath!], with: .fade)
        case .update:
            tableView.reloadRows(at: [indexPath!], with: .fade)
        case .move:
            tableView.moveRow(at: indexPath!, to: newIndexPath!)
        @unknown default:
            fatalError()
        }
    }

    func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        tableView.endUpdates()
    }

[在我看来，如果我按下方便的花花绿绿的按钮，则桌面视图应该使用新的“ Hello World”刷新-但我什么也没得到。没有打印，没有错误。没有。

我已经从AppDelegate上下文一直检查到上下文引用，直到发送按钮-相同的地址。我检查了fetchedResultsController及其委托-不是nil。

我对所发生的事情一无所知，完全不知所措。有什么想法吗？

Answer 1

[如果其他人遇到此问题-我的提取请求未正确连接（？）到CoreData。如@vadian所述，NSSortDescriptor为必需。

更重要的是，我在注释中错过的浮动谓词是错误的；我在数据结构中比较的id是UUID-但是，我使用CVarArg作为String。

当我更改谓词以使用argumentArray时，所有问题都已修复。

因此，更改此：

        let predicate = NSPredicate(format: "chat.id == %@", "12345")

至此：

        let predicate = NSPredicate(format: "chat.id == %@",  argumentArray: [SomeUUID])