ios - 删除后重新加载应用程序时,TableView 中的 CoreData 条目重新出现
问题描述
所以我想删除我的表格视图中的条目。我目前正在使用 coredata。发生的情况是,当我在我的应用程序中删除我的条目时,它似乎已被删除,但是当我重新加载应用程序时,该条目会重新出现。这很可能是因为我没有删除 coredata 本身中的条目,只有在有意义的情况下才在 tableview 中删除它。
我遵循了多个关于如何实现 tableview 控制器来处理包括删除在内的更改的指南。这就是为什么我对我的代码不起作用的原因感到困惑。
我的视图控制器:
import UIKit
import CoreData
class ViewController: UITableViewController, NSFetchedResultsControllerDelegate {
let cellId = "cellId"
fileprivate lazy var fetchedResultsController: NSFetchedResultsController<AlarmItem> = {
//create fetch request
let fetchRequest: NSFetchRequest<AlarmItem> = AlarmItem.fetchRequest()
//configure fetch request
fetchRequest.sortDescriptors = [NSSortDescriptor(key: "alarmAttributes", ascending: true)]
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
let fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
let managedObjectContext = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
fetchedResultsController.delegate = self
return fetchedResultsController
}()
func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
tableView.beginUpdates()
}
func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
tableView.endUpdates()
}
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
switch(type) {
case .insert:
if let indexPath = newIndexPath {
tableView.insertRows(at: [indexPath], with: .fade)
}
break;
case .delete:
if let indexPath = indexPath {
tableView.deleteRows(at: [indexPath], with: .fade)
}
break;
case .update:
//this is mostlikely where the problem lies
//self.tableView.reloadData()
if let indexPath = indexPath, let cell = tableView.cellForRow(at: indexPath) {
configureCell(cell, at: indexPath)
}
break;
case .move:
if let indexPath = indexPath {
tableView.deleteRows(at: [indexPath], with: .fade)
}
if let newIndexPath = newIndexPath {
tableView.insertRows(at: [newIndexPath], with: .fade)
}
break;
@unknown default:
print("Something odd is happening")
}
}
override func viewDidLoad() {
super.viewDidLoad()
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
do {
try fetchedResultsController.performFetch()
} catch let err as NSError {
print("Failed to fetch items", err)
}
}
@objc func addAlarmItem(_ sender: AnyObject) {
//print("this works")
let alertController = UIAlertController(title: "Add New Item", message: "Please fill in the blanks", preferredStyle: .alert)
let saveAction = UIAlertAction(title: "Save", style: .default) { [unowned self] action in
//combined string of attributes
let myStrings: [String] = alertController.textFields!.compactMap { $0.text }
let myText = myStrings.joined(separator: ", ")
self.save(myText)
self.tableView.reloadData()
}
let cancelAction = UIAlertAction(title: "Cancel", style: .destructive, handler: nil)
alertController.addTextField { (textField) in
textField.placeholder = "Enter Name of Engineer"
}
alertController.addTextField { (textField) in
textField.placeholder = "Enter Date of Alarm in DD/MM/YYYY"
}
alertController.addTextField { (textField) in
textField.placeholder = "Enter Time of Alarm in 24h (eg: 2300)"
}
alertController.addTextField { (textField) in
textField.placeholder = "Please indicate True/False (type True or False)"
}
alertController.addTextField { (textField) in
textField.placeholder = "Insert comments (if any), or NIL"
}
//work on fullscreen display
//this does not work
//alertController.modalPresentationStyle = UIModalPresentationStyle.overFullScreen
alertController.addAction(saveAction)
alertController.addAction(cancelAction)
present(alertController, animated: true, completion: nil)
}
func save(_ itemName: String) {
guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return }
let managedContext = appDelegate.persistentContainer.viewContext
let entity = NSEntityDescription.entity(forEntityName: "AlarmItem", in: managedContext)!
let item = NSManagedObject(entity: entity, insertInto: managedContext)
item.setValue(itemName, forKey: "alarmAttributes")
do {
try managedContext.save()
tableView.reloadData()
} catch let err as NSError {
print("Failed to save an item", err)
}
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int{
let sectionInfo = fetchedResultsController.sections![section]
return sectionInfo.numberOfObjects
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: cellId, for: indexPath)
let alarmItem = fetchedResultsController.object(at: indexPath) as NSManagedObject
cell.textLabel?.text = alarmItem.value(forKeyPath: "alarmAttributes") as? String
return cell
}
func tableView(_ tableView: UITableView!, canEditRowAtIndexPath indexPath: NSIndexPath!) -> Bool {
return true
}
override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
tableView.deselectRow(at: indexPath, animated: true)
}
override func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath) {
guard editingStyle == .delete else { return }
//fetch
let toBeDeleted = fetchedResultsController.object(at: indexPath)
//delete
fetchedResultsController.managedObjectContext.delete(toBeDeleted)
}
func tableView(_tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "AlarmItem", for: indexPath)
configureCell(cell, at: indexPath)
return cell
}
func configureCell(_ cell: UITableViewCell, at indexPath: IndexPath) {
let alarmItem = fetchedResultsController.object(at: indexPath)
//configure cell
cell.textLabel?.text = alarmItem.value(forKeyPath: "alarmAttributes") as? String
}
}
解决方案
请加:
fetchedResultsController.managedObjectContext.save()
作为函数的最后一行:
func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath)
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