我知道有相同错误的无数问题，但似乎没有一个解决方案可行。
我想制作一个博客阅读器应用程序，用于保存和从CoreData中提取数据。我能够将JSON结果保存到CoreData中，但是当我尝试检索它以在tableView中显示时，它会在行上与fatal error: unexpectedly found nil while unwrapping an Optional value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()
}
}
tableview显示文本＆＃34;博客项目＆＃34;当我返回1并分别从numberOfSectionsInTableView和func tableView(tableView: UITableView, numberOfRowsInSection section: Int)返回20时，20次，并且数据显示在控制台中。但是，当我注释掉手动返回值，并想要使用原始值时，应用程序在上面提到的行上崩溃了。
我猜是否与fetchedResultsController有关。
请帮助。自昨天以来我一直坚持这个
答案 0 :(得分：5)
您需要设置self.managedObjectContext（它当前为零，这会导致您的错误）。你可以在视图控制器生命周期早期调用的一个函数中设置它，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?
...