fetchedResultsController 核心数据致命错误：在展开可选值时意外发现 nil

Posted 2023-02-27

【中文标题】fetchedResultsController 核心数据致命错误：在展开可选值时意外发现 nil

【英文标题】：fetchedResultsController core data fatal error: unexpectedly found nil while unwrapping an Optional value

【发布时间】：2015-01-30 10:09:23

【问题描述】：

我知道有无数个问题都有相同的错误，但似乎没有一个解决方案有效。

我想制作一个博客阅读器应用程序，它可以从 CoreData 保存和获取数据。我可以将 JSON 结果保存到 CoreData 中，但是当我尝试检索它以显示在 tableView 中时，它会因在线 fatal error: unexpectedly found nil while unwrapping an Optional value 而崩溃

let entity = NSEntityDescription.entityForName("Blog", inManagedObjectContext:self.managedObjectContext!)

这是我的代码：

import UIKit
import CoreData

var activeItem:String = ""

class CenterViewController: UIViewController,
  UIWebViewDelegate, NSFetchedResultsControllerDelegate,     
 SidePanelViewControllerDelegate 
 var detailViewController: DetailViewController? = nil
 var managedObjectContext: NSManagedObjectContext? = nil

@IBOutlet weak var titleLabel: UILabel!
@IBOutlet weak var tableview: UITableView!
@IBOutlet weak var webview2: UIWebView!


var delegate: CenterViewControllerDelegate?

// MARK: Button actions

@IBAction func kittiesTapped(sender: AnyObject) 
delegate?.toggleLeftPanel?()
 

@IBAction func puppiesTapped(sender: AnyObject) 
delegate?.toggleRightPanel?()
 

  func animalSelected(animal: Animal) 

var appDel: AppDelegate = UIApplication.sharedApplication().delegate as AppDelegate
var context: NSManagedObjectContext = appDel.managedObjectContext!
var newBlogItem:NSManagedObject
let session = NSURLSession.sharedSession()
var error : NSError?

 let task = session.dataTaskWithURL(animal.url!, completionHandler: data, response, error -> Void in

    if (error != nil)
        println(error)

    else


       let jsonResult = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: nil) as NSDictionary
        var posts = [[String:String]()]

        var post:AnyObject

        var authorDictionary:AnyObject
        var newBlogItem:NSManagedObject
        for var i = 0; i < jsonResult["posts"]!.count; i++

        
        posts.append([String:String]())
        post = jsonResult["posts"]![i] as NSDictionary
        posts[i]["title"] = post["title"] as? NSString
        posts[i]["publishedDate"] = post["date"] as? NSString
        posts[i]["content"] = post["content"] as? NSString
        authorDictionary = post["author"] as NSDictionary
        posts[i]["author"] = post["name"] as? NSString



            newBlogItem = NSEntityDescription.insertNewObjectForEntityForName("Blog", inManagedObjectContext: context) as NSManagedObject
            newBlogItem.setValue(posts[i]["title"], forKey: "title")
            newBlogItem.setValue(posts[i]["publishedDate"], forKey: "publishedDate")
            newBlogItem.setValue(posts[i]["content"], forKey: "content")
            newBlogItem.setValue(posts[i]["author"], forKey: "author")

            context.save(nil)

        
        var request = NSFetchRequest(entityName: "Blog")
        request.returnsObjectsAsFaults = false
        var results = context.executeFetchRequest(request, error: nil)
        println(results)

  

)

task.resume()
   delegate?.collapseSidePanels?()


// MARK: - Table View

 func numberOfSectionsInTableView(tableView: UITableView) -> Int 


    return self.fetchedResultsController.sections!.count
  // return 1


 func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int 
  let sectionInfo = self.fetchedResultsController.sections![section] as NSFetchedResultsSectionInfo
   return sectionInfo.numberOfObjects
   //return 20


 func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell 
    let cell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath) as UITableViewCell
  // self.configureCell(cell, atIndexPath: indexPath)
   cell.textLabel?.text = "blog item"
    return cell


 func tableView(tableView: UITableView, canEditRowAtIndexPath indexPath: NSIndexPath) -> Bool 
    // Return false if you do not want the specified item to be editable.
    return true


 func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) 
    if editingStyle == .Delete 
        let context = self.fetchedResultsController.managedObjectContext
        context.deleteObject(self.fetchedResultsController.objectAtIndexPath(indexPath) as NSManagedObject)

        var error: NSError? = nil
        if !context.save(&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()
        
    


func configureCell(cell: UITableViewCell, atIndexPath indexPath: NSIndexPath) 
    let object = self.fetchedResultsController.objectAtIndexPath(indexPath) as NSManagedObject
    cell.textLabel?.text = object.valueForKey("title")!.description




// MARK: - Fetched results controller

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

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

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

        // Edit the sort key as appropriate.
        let sortDescriptor = NSSortDescriptor(key: "publishedDate", ascending: false)
        let sortDescriptors = [sortDescriptor]

        fetchRequest.sortDescriptors = [sortDescriptor]

        // 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: nil, cacheName: "Slide Out Tutorial")
        aFetchedResultsController.delegate = self
        _fetchedResultsController = aFetchedResultsController

        var error: NSError? = nil
        if !_fetchedResultsController!.performFetch(&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!

var _fetchedResultsController: NSFetchedResultsController? = nil

func controllerWillChangeContent(controller: NSFetchedResultsController) 
    self.tableview.beginUpdates()


func controller(controller: NSFetchedResultsController, didChangeSection sectionInfo: NSFetchedResultsSectionInfo, atIndex sectionIndex: Int, forChangeType type: NSFetchedResultsChangeType) 
    switch type 
    case .Insert:
        self.tableview.insertSections(NSIndexSet(index: sectionIndex), withRowAnimation: .Fade)
    case .Delete:
        self.tableview.deleteSections(NSIndexSet(index: sectionIndex), withRowAnimation: .Fade)
    default:
        return
    


func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath) 
    switch type 
    case .Insert:
        tableview.insertRowsAtIndexPaths([newIndexPath], withRowAnimation: .Fade)
    case .Delete:
        tableview.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
    case .Update:
        self.configureCell(tableview.cellForRowAtIndexPath(indexPath)!, atIndexPath: indexPath)
    case .Move:
        tableview.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
        tableview.insertRowsAtIndexPaths([newIndexPath], withRowAnimation: .Fade)
    default:
        return
    


func controllerDidChangeContent(controller: NSFetchedResultsController) 
    self.tableview.endUpdates()

当我分别从numberOfSectionsInTableView和func tableView(tableView: UITableView, numberOfRowsInSection section: Int)返回1和返回20时，tableview显示文本“blog item”20次，数据显示在控制台中。但是当我注释掉手动返回值并想使用原始返回值时，应用程序在上面提到的行上崩溃了。

我只是猜测它是否与 fetchedResultsController 有关。

请帮忙。从昨天开始我就一直坚持这个

【问题讨论】：

你需要设置self.managedObjectContext的值，它被初始化为nil，然后永远不会设置。

@pbasdf 你能帮我解决这个问题吗..m 是 Swift 的新手，并通过混合不同的单个项目设法到达这里

【参考方案1】：

您需要设置self.managedObjectContext（它当前为 nil，这会导致您的错误）。您可以在视图控制器生命周期早期调用的函数之一中设置它，例如viewDidLoad，但另一种方法是在初始化 fetchedResultsController 时设置它，如下所示：

var fetchedResultsController: NSFetchedResultsController 
    if _fetchedResultsController != nil 
        return _fetchedResultsController!
    
    var appDel: AppDelegate = UIApplication.sharedApplication().delegate as AppDelegate
    self.managedObjectContext = appDel.managedObjectContext

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

【讨论】：

还发现我忘了实例化我的上下文，一个我没在看的地方，谢谢！！

@pbasdf 哦，伙计！你刚刚救了我的命！谢谢。在调试器中，我一直在努力解决这个问题大约 8 个小时……谢谢！