NSFetchedResultsController 在错误的 indexPath 中添加项目

Question

我编写了简单的计数器应用程序。它使用 CoreData 来存储数据。在模型中，我有一个名为“Counter”的实体，其属性为“value”（Int64）和“position”（Int16）。第二个属性是 tableView 中的位置。用户可以添加、删除或增加计数器。我还使用 NSFetchedResultsController 来填充我的 tableView。应用程序可以工作，但是当我添加 5 个计数器、更改它们的值、删除第二个和第三个值并添加新的值时，计数器将不会插入到 tableView 的末尾（这里是视频https://youtu.be/XXyuEaobd3c）。我的代码有什么问题？

import UIKit
import CoreData

class TableViewController: UITableViewController, NSFetchedResultsControllerDelegate {

let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext

var frc: NSFetchedResultsController<Counter> = {
    let fetchRequest: NSFetchRequest<Counter> = Counter.fetchRequest()
    let sortDescriptor = NSSortDescriptor(key: "position", ascending: true)
    fetchRequest.sortDescriptors = [sortDescriptor]
    let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
    let frc = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
    do {
        try frc.performFetch()
    } catch {
        print(error)
    }
    return frc
}()


@IBAction func addCounter(_ sender: UIBarButtonItem) {
    let counter = Counter(context: context)
    counter.value = 0
    counter.position = Int16(frc.fetchedObjects!.count)
    do {
        try context.save()
    } catch {
        print(error)
    }

}

@IBAction func longPressed(_ sender: UILongPressGestureRecognizer) {
    if sender.state == UIGestureRecognizerState.began {
        let touchPoint = sender.location(in: self.view)
        if let indexPath = tableView.indexPathForRow(at: touchPoint) {
            // your code here, get the row for the indexPath or do whatever you want
            let counter = frc.object(at: indexPath)
            counter.value = 0

            do {
                try context.save()
            } catch {
                print(error)
            }
        }
    }

}


override func viewDidLoad() {
    super.viewDidLoad()

    frc.delegate = self
}


// MARK: - Table view data source

override func numberOfSections(in tableView: UITableView) -> Int {
    guard let sections = frc.sections?.count else {return 0}
    return sections
}

override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    guard let sections = frc.sections else {return 0}
    return sections[section].numberOfObjects
}


override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath)
    let counter = frc.object(at: indexPath)
    cell.textLabel!.text! = String(counter.value)

    return cell
}

func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
    tableView.beginUpdates()
}

func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
    switch type {
    case .insert:
        guard let indexPath = newIndexPath else {return}
        tableView.insertRows(at: [indexPath], with: .fade)
    case .delete:
        guard let indexPath = indexPath else {return}
        tableView.deleteRows(at: [indexPath], with: .fade)
    case .update:
        guard let indexPath = indexPath else {return}
        let cell = tableView.cellForRow(at: indexPath)
        let counter = frc.object(at: indexPath)
        cell?.textLabel?.text = String(counter.value)
    default:
        break
    }
}

func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
    tableView.endUpdates()
}

override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    let counter = frc.object(at: indexPath)
    counter.value += Int64(1)

    do {try context.save()}
    catch {print(error)}

    tableView.deselectRow(at: indexPath, animated: true)
}

   // Override to support editing the table view.
override func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCellEditingStyle, forRowAt indexPath: IndexPath) {
    if editingStyle == .delete {
            let counter = frc.object(at: indexPath)
            context.delete(counter)

        do {
            try context.save()
        } catch {
            print(error)
        }
    }
}

}

Answer 1

您以错误的方式添加职位。 假设你有

A1、A2、A3、A4、A5

然后删除A2、A3

在那之后你有 A1、A4、A5

所以添加新的是 B3，因为现在计数是 3 A1、B3、A4、A5

添加另一行变为 B4，因此它可以在 A4 之前或之后的任何位置。

这个顺序是由于位置上的排序顺序。

您可以通过获取最后获取的对象并增加位置和结果来解决此问题：

A1、A4、A5、B6、B7