Question

我正在尝试在UITableView中使用NSFetchedResultsController ..但由于某种原因，当我添加新条目时，NSFetchedResultsControllerDelegate不会被触发。这是完整的代码

import UIKit
import CoreData

let coreDataStack = CoreDataStack()
class CDListViewController: UITableViewController, NSFetchedResultsControllerDelegate {


    var fetchedResultsController: NSFetchedResultsController {
        if _fetchedResultsController != nil {
            return _fetchedResultsController!
        }
        let fRequest = fetchRequest()

        let aFetchedResultsController = NSFetchedResultsController(fetchRequest: fRequest, managedObjectContext: coreDataStack.managedObjectContext!, sectionNameKeyPath: nil, cacheName: nil)

        aFetchedResultsController.delegate = self
        _fetchedResultsController = aFetchedResultsController

        var error: NSError? = nil
        if !_fetchedResultsController!.performFetch(&error) {
        }
        println(error)

        return _fetchedResultsController!
    }

    var _fetchedResultsController: NSFetchedResultsController? = nil

    func fetchRequest() -> NSFetchRequest {
        let fetchRequest = NSFetchRequest(entityName: "Menu")

        // Set the batch size to a suitable number.
        fetchRequest.fetchBatchSize = 2

        // Edit the sort key as appropriate.
        let sortDescriptor = NSSortDescriptor(key: "createdAt", ascending: false)

        fetchRequest.sortDescriptors = [sortDescriptor]
        return fetchRequest
    }


    override func viewDidLoad() {
        super.viewDidLoad()
        fetchedResultsController.delegate = self
        print(fetchedResultsController)
//        fetchedResultsController?.performFetch(nil)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()

    }

    override func tableView(tableView: UITableView, editingStyleForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCellEditingStyle {
        return UITableViewCellEditingStyle.Delete
    }

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

    override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        let menus = fetchedResultsController.fetchedObjects as [Menu]
        return menus.count
    }


    override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath) as UITableViewCell
        let curr = fetchedResultsController.objectAtIndexPath(indexPath) as Menu
        // Configure the cell...
        cell.textLabel?.text = curr.text
        return cell
    }



    // Override to support conditional editing of the table view.
    override func tableView(tableView: UITableView, canEditRowAtIndexPath indexPath: NSIndexPath) -> Bool {
        // Return NO if you do not want the specified item to be editable.
        return true
    }



    // Override to support editing the table view.

    func controllerWillChangeContent(controller: NSFetchedResultsController) {
        println("Coming in here")
        self.tableView.beginUpdates()
    }

    func controllerDidChangeContent(controller: NSFetchedResultsController) {
        self.tableView.endUpdates()
    }




    // Override to support editing the table view.
    override func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) {
        let entry = self.fetchedResultsController.objectAtIndexPath(indexPath) as Menu
        coreDataStack.managedObjectContext?.deleteObject(entry)
        coreDataStack.saveContext()
    }

    func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?) {
        switch(type) {
        case NSFetchedResultsChangeType.Insert : self.tableView.insertRowsAtIndexPaths([newIndexPath!], withRowAnimation: UITableViewRowAnimation.Automatic)
            break
        case NSFetchedResultsChangeType.Delete : self.tableView.deleteRowsAtIndexPaths([indexPath!], withRowAnimation: UITableViewRowAnimation.Automatic)
            break
        case NSFetchedResultsChangeType.Update : self.tableView.reloadRowsAtIndexPaths([indexPath!], withRowAnimation: UITableViewRowAnimation.Automatic)
        default:
            println("Nothing")
        }
    }

    func controller(controller: NSFetchedResultsController, didChangeSection sectionInfo: NSFetchedResultsSectionInfo, atIndex sectionIndex: Int, forChangeType type: NSFetchedResultsChangeType) {
        switch(type) {
        case NSFetchedResultsChangeType.Insert : self.tableView.insertSections(NSIndexSet(index: sectionIndex), withRowAnimation: UITableViewRowAnimation.Automatic)
            break
        case NSFetchedResultsChangeType.Delete : self.tableView.deleteSections(NSIndexSet(index: sectionIndex), withRowAnimation: UITableViewRowAnimation.Automatic)
            break
        default:
            println("Nothing")
        }
    }

}

当我向上下文添加条目并保存内容时，不会调用controllerWillChangeContent和controllerDidChangeContent。我确保上下文已保存，因为如果我重新启动应用程序，我可以看到最近添加的条目任何人都可以找到上面编写的代码的任何问题吗？

Answer 1

我注意到你设置了两次委托。一旦进入计算属性，一次进入viewDidLoad。我认为您的问题可能源于您首先在计算属性中为aFetchedResultsController设置它，因此，在调用aFetchedResultsController委托方法时调用委托方法（他们不是）。删除计算属性中的委派任务（aFetchedResultsController.delegate = self）应解决此问题。

NSFetchedResultsControllerDelegate：controllerDidChangeContent在iOS 8中不起作用

1 个答案: