【发布时间】：2016-06-08 10:09:08
【问题描述】：
我正在解析来自 data source 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在读取时他们被发现为零。 在函数读取的返回结果中，错误是“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.
}
}
【问题讨论】：
-
您似乎总是只保存每个核心数据条目的一个属性，而不是全部三个。这是故意的吗？这可能会导致错误。
-
是的，我打算这样做。 @vadian
-
那么你必须确保读取函数总是返回一个非可选值或将返回值更改为一个可选值（并使用 Swift 原生类型
String而不是NSString） -
@vadian 我正在调用 save 并在 prepareForSegue 函数中读取价格和日期
-
在读取函数的末尾
result被解包。如果是nil，应用就会崩溃。