问题
I am trying to simply store and retrieve CoreData (something that I've done successfully before with swift). I was getting a nil for data, but now (not sure what changed) I'm not getting an error, just nothing showing in the tableview. I'm not sure if it's a problem in storing or retrieving the object. I've followed how I did it in another app of mine as closely as possible, but there seems to be some fundamental thing that I'm not getting. Here's what I have.
My model:
import Foundation
import CoreData
@objc(DataModel)
class DataModel: NSManagedObject {
@NSManaged var itemName: String
@NSManaged var quantity: NSNumber
@NSManaged var price: NSNumber
}
In my tableviewcontroller with static cells for text fields that I want to save data from:
import UIKit
import CoreData
class NewItemTableViewController: UITableViewController {
@IBOutlet weak var itemNameTextField: UITextField!
@IBOutlet weak var itemPriceTextField: UITextField!
@IBOutlet weak var itemQuantityTextField: UITextField!
override func viewDidLoad() {
super.viewDidLoad()
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
@IBAction func saveButton(sender: AnyObject) {
//CoreData
let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate
let managedContext : NSManagedObjectContext = appDelegate.managedObjectContext!
let entity = NSEntityDescription.entityForName("Item", inManagedObjectContext: managedContext)
var newItem = DataModel(entity: entity!, insertIntoManagedObjectContext: managedContext)
newItem.itemName = itemNameTextField.text
//newItem.price = itemPriceTextField.text
//newItem.quantity = itemQuantityTextField
managedContext.save(nil)
self.navigationController?.popToRootViewControllerAnimated(true)
}
@IBAction func cancelButton(sender: AnyObject) {
self.navigationController?.popToRootViewControllerAnimated(true)
}
And in my tableviewcontroller that I want to retrieve the data an show in dynamic cells:
class ItemListTableViewController: UITableViewController {
var items : Array<AnyObject> = []
override func viewDidLoad() {
super.viewDidLoad()
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
// MARK: - Table view data source
override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
// #warning Potentially incomplete method implementation.
// Return the number of sections.
return 1
}
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
// #warning Incomplete method implementation.
// Return the number of rows in the section.
return items.count
}
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let CellID: NSString = "cell"
var cell: UITableViewCell = tableView.dequeueReusableCellWithIdentifier(CellID) as UITableViewCell
var data: NSManagedObject = items[indexPath.row] as NSManagedObject
var itemName = data.valueForKey("itemName") as String
var price = data.valueForKey("price") as NSNumber
var quantity = data.valueForKey("quantity") as NSNumber
cell.textLabel!.text! = "\(itemName)"
cell.detailTextLabel!.text! = "Price: \(price) - Quantity: \(quantity)"
return cell
}
Any help on a concept I might have missed somewhere in here would be appreciated! Thanks.
Update: so I've redone my code to be modeled after @Bluehound 's suggestion. but I'm still getting an error: not sure how to fix it.
回答1:
When using core data and a tableview, you should use NSFetchedResultsController. This essentially retrieves data from core data and organizes it by section and indexPath so it can easily be set as the data source of the tableView. Here is a complete implementation of a potential UITableViewController that conforms to NSFetchedResultsControllerDelegate:
import Foundation
import UIKit
import CoreData
class HomeViewController: UITableViewController, NSFetchedResultsControllerDelegate {
let managedObjectContext: NSManagedObjectContext? = (UIApplication.sharedApplication().delegate as? AppDelegate)?.managedObjectContext
var fetchedResultsController: NSFetchedResultsController?
override func viewDidLoad() {
super.viewDidLoad()
fetchedResultsController = NSFetchedResultsController(fetchRequest: allEmployeesFetchRequest(), managedObjectContext: managedObjectContext!, sectionNameKeyPath: nil, cacheName: nil)
fetchedResultsController?.delegate = self
fetchedResultsController?.performFetch(nil)
}
func allEmployeesFetchRequest() -> NSFetchRequest {
var fetchRequest = NSFetchRequest(entityName: "Employee")
let sortDescriptor = NSSortDescriptor(key: "nameLast", ascending: true)
fetchRequest.predicate = nil
fetchRequest.sortDescriptors = [sortDescriptor]
fetchRequest.fetchBatchSize = 20
return fetchRequest
}
//MARK: UITableView Data Source and Delegate Functions
override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
return fetchedResultsController?.sections?.count ?? 0
}
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return fetchedResultsController?.sections?[section].numberOfObjects ?? 0
}
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("HomeCell", forIndexPath: indexPath) as UITableViewCell
if let cellContact = fetchedResultsController?.objectAtIndexPath(indexPath) as? Employee {
cell.textLabel?.text = "\(cellContact.nameLast), \(cellContact.nameFirst)"
}
return cell
}
//MARK: NSFetchedResultsController Delegate Functions
func controller(controller: NSFetchedResultsController, didChangeSection sectionInfo: NSFetchedResultsSectionInfo, atIndex sectionIndex: Int, forChangeType type: NSFetchedResultsChangeType) {
switch type {
case NSFetchedResultsChangeType.Insert:
tableView.insertSections(NSIndexSet(index: sectionIndex), withRowAnimation: UITableViewRowAnimation.Fade)
break
case NSFetchedResultsChangeType.Delete:
tableView.deleteSections(NSIndexSet(index: sectionIndex), withRowAnimation: UITableViewRowAnimation.Fade)
break
case NSFetchedResultsChangeType.Move:
break
case NSFetchedResultsChangeType.Update:
break
default:
break
}
}
override func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) {
if editingStyle == .Delete {
}
switch editingStyle {
case .Delete:
managedObjectContext?.deleteObject(fetchedResultsController?.objectAtIndexPath(indexPath) as Employee)
managedObjectContext?.save(nil)
case .Insert:
break
case .None:
break
}
}
func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?) {
switch type {
case NSFetchedResultsChangeType.Insert:
tableView.insertRowsAtIndexPaths(NSArray(object: newIndexPath!), withRowAnimation: UITableViewRowAnimation.Fade)
break
case NSFetchedResultsChangeType.Delete:
tableView.deleteRowsAtIndexPaths(NSArray(object: indexPath!), withRowAnimation: UITableViewRowAnimation.Fade)
break
case NSFetchedResultsChangeType.Move:
tableView.deleteRowsAtIndexPaths(NSArray(object: indexPath!), withRowAnimation: UITableViewRowAnimation.Fade)
tableView.insertRowsAtIndexPaths(NSArray(object: newIndexPath!), withRowAnimation: UITableViewRowAnimation.Fade)
break
case NSFetchedResultsChangeType.Update:
tableView.cellForRowAtIndexPath(indexPath!)
break
default:
break
}
}
func controllerWillChangeContent(controller: NSFetchedResultsController) {
tableView.beginUpdates()
}
func controllerDidChangeContent(controller: NSFetchedResultsController) {
tableView.endUpdates()
}
}
See a sample GitHub project here.
来源：https://stackoverflow.com/questions/27513689/retrieving-core-data-into-tableview-cells-swift