读取核心数据时出错:ios swift

Question

我正在分析来自该数据源的数据，并且它们被正确解析，然后我将数据(标题、价格和日期)保存到CoreData，标题被保存并正确读取，价格和日期被保存，但读取时发现它们为零。在函数读取中返回结果时，错误为"致命错误：在展开可选值时意外发现nil"。这是MyTableViewController.swift:

import UIKit
import CoreData
class MyTableViewController: UITableViewController {
@IBOutlet var songsTable: UITableView!
let viewModel = ViewModel()
var imageCache = [String:UIImage]()
var songs = [NSManagedObject]()
let firstDefaults = NSUserDefaults.standardUserDefaults()
let secondDefaults = NSUserDefaults.standardUserDefaults()

override func viewDidLoad() {
super.viewDidLoad()
self.refresh()
self.refreshControl = UIRefreshControl()
self.refreshControl?.addTarget(self, action: #selector(MyTableViewController.refresh), forControlEvents: .ValueChanged)
}
func refresh() {
viewModel.fetch {
dispatch_async(dispatch_get_main_queue()) {
self.tableView.reloadData()
self.refreshControl?.endRefreshing()
}
}

}

override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
return self.viewModel.numberOfSections()
}
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return self.viewModel.numberOfItemsInSection(section)
}
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("cell", forIndexPath: indexPath) as! MyTableViewCell
let integer: NSInteger = indexPath.row
if !firstDefaults.boolForKey("titlesSaved") {
saveItem(self.viewModel.titleForItemAtIndexPath(indexPath), id: integer, name: "title")
firstDefaults.setBool(true, forKey: "titlesSaved")
}
cell.songTitle.text = read(integer,item: "title") as String
//images are not displayed
cell.songImage?.image = UIImage(named: "Blank52.png")
let urlString = self.viewModel.imageForItemAtIndexPath(indexPath)
let imgURL: NSURL = NSURL(string: urlString)!
let request: NSURLRequest = NSURLRequest(URL: imgURL)
NSURLConnection.sendAsynchronousRequest(
request, queue: NSOperationQueue.mainQueue(),
completionHandler: {(response: NSURLResponse?, data: NSData?, error: NSError?) -> Void in
if error == nil {
cell.songImage.image = UIImage(data: data!)
}
})
let thumbnailURLString = self.viewModel.imageForItemAtIndexPath(indexPath)
let thumbnailURL = NSURL(string: thumbnailURLString)!
//if image is cached
if let img = imageCache[thumbnailURLString] {
cell.songImage?.image = img
print("image is cached")
}
else {
// The image isn't cached, download the img data
// We should perform this in a background thread
let request: NSURLRequest = NSURLRequest(URL: thumbnailURL)
let mainQueue = NSOperationQueue.mainQueue()
NSURLConnection.sendAsynchronousRequest(request, queue: mainQueue, completionHandler: { (response, data, error) -> Void in
if error == nil {
// Convert the downloaded data in to a UIImage object
let image = UIImage(data: data!)
// Store the image in to our cache
self.imageCache[thumbnailURLString] = image
// Update the cell
dispatch_async(dispatch_get_main_queue(), {
if let cellToUpdate = tableView.cellForRowAtIndexPath(indexPath) as! MyTableViewCell?{
cellToUpdate.songImage?.image = image
}
})
}
else {
print("Error: (error!.localizedDescription)")
}
})
}
return cell
}
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if let detailsViewController: DetailsViewController = segue.destinationViewController as? DetailsViewController {
let songIndex = songsTable!.indexPathForSelectedRow
let integer: NSInteger = songIndex!.row
//if !secondDefaults.boolForKey("pricesAndDatesSaved") {
saveItem(self.viewModel.priceForItemAtIndexPath(songIndex!), id: integer, name: "price")
saveItem(self.viewModel.dateForItemAtIndexPath(songIndex!), id: integer, name: "date")
//secondDefaults.setBool(true, forKey: "pricesAndDatesSaved")
// }
detailsViewController.songPrice = read(integer,item: "price") as String
detailsViewController.songDate = read(integer,item: "date") as String
// detailsViewController.songPrice = self.viewModel.priceForItemAtIndexPath(songIndex!)
//detailsViewController.songDate = self.viewModel.dateForItemAtIndexPath(songIndex!)
}
}
func saveImage(id:Int,image:UIImage)
{
let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
let managedContext = appDelegate.managedObjectContext
let entity = NSEntityDescription.entityForName("Song",
inManagedObjectContext: managedContext)
let options = NSManagedObject(entity: entity!,
insertIntoManagedObjectContext:managedContext)
let newImageData = UIImageJPEGRepresentation(image,1)
options.setValue(id, forKey: "index")
options.setValue(newImageData, forKey: "image")

}
func saveItem(item:String, id:Int, name: String)
{
print("my (name) is (item)")
print("my id is (id)")
let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
let managedContext = appDelegate.managedObjectContext
let entity = NSEntityDescription.entityForName("Song",
inManagedObjectContext: managedContext)
let options = NSManagedObject(entity: entity!,
insertIntoManagedObjectContext:managedContext)
options.setValue(id, forKey: "index")
switch name {
case "title":
options.setValue(item, forKey: "title")
case "price":
options.setValue(item, forKey: "price")
case "date":
options.setValue(item, forKey: "date")
default:
print("error in switch")
}

do{
try managedContext.save()
} catch let error as NSError{
print("could not save title (error)")
}
}
func read(id: Int, item:String)-> NSString
{
print("my id in read func is (id)")
let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
let managedContext = appDelegate.managedObjectContext
let fetchRequest = NSFetchRequest(entityName: "Song")
var result: NSString? = nil
do {
let results = try managedContext.executeFetchRequest(fetchRequest)
let single_result = results[id]
switch item {
case "title":
result = single_result.valueForKey("title") as? NSString
case "price":
result = single_result.valueForKey("price") as? NSString
case "date":
result = single_result.valueForKey("date") as? NSString
default:
print("error in switch in read function")
}
print ("i am reading the (item): (result)")
}catch let error as NSError{
print("could not fetch title (error)")
}
return result!
}

这是DetailsViewController.swift

import UIKit
import CoreData
class DetailsViewController: UIViewController {
@IBOutlet weak var price: UILabel!
@IBOutlet weak var releaseDate: UILabel!
var song: ViewModel?
var songPrice: String = ""
var songDate: String = ""
override func viewDidLoad() {
super.viewDidLoad()
price.text = "Price = (self.songPrice)"
print(self.songPrice)
print(self.songDate)
releaseDate.text = "Release date is: (self.songDate)"
// Do any additional setup after loading the view.
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}

Answer 1

您正在执行以下操作：

1. 使用标题和ID调用saveItem
   1. 创建新的NSManagedObject
   2. 设置新NSManagedObject的标题
2. 使用价格和ID调用saveItem
   1. 创建新的NSManagedObject
   2. 设置新NSManagedObject的价格
3. 使用日期和ID调用saveItem
   1. 创建新的NSManagedObject
   2. 设置新NSManagedObject的日期

您想要做的是：

1. 使用标题和ID调用saveItem
   1. 创建新的NSManagedObject
   2. 设置新NSManagedObject的标题
2. 使用价格和ID调用updateItem
   1. FETCH基于ID的现有对象
   2. 设置新NSManagedObject的价格
3. 使用日期和ID调用updateItem
   1. FETCH基于ID的现有对象
   2. 设置新NSManagedObject的命运

或者更好：

1. 使用标题、价格、日期和ID调用saveUpdateItem
   1. 如果项目存在，则提取它，否则创建它
   2. 更新项目

您将返回一个nil，因为您为每个过程创建THREE对象，而不是ONE。