对 UITableviewCell 重新排序，其中数据存储在 CoreData 中

Question

我创建了一个 iOS 应用程序来存储一个列表（比如名称）。此外，我还添加了滑动删除、搜索和重新排序表格行等功能。以下是应用截图：

我面临的问题是，当我首先通过单击编辑按钮重新排序列表时，似乎代码工作正常。在下面的屏幕中，我交换了前两行，这似乎是我想要的。 看下面两张截图：

但是当我执行搜索功能时，已互换的行会恢复到其原始位置，如第一张图片所示。因为我使用 CoreData 作为持久存储。我正在尝试找到解决方案，但到目前为止还没有成功。这是执行搜索功能后的样子：

这是我的代码：

import UIKit
import CoreData

class ViewController: UIViewController, UISearchBarDelegate, UISearchDisplayDelegate {

    // IBOutlets
    @IBOutlet weak var tableView: UITableView!
    @IBOutlet weak var searchBar: UISearchBar!
    @IBOutlet weak var editButton: UIBarButtonItem!

    // Global declaration
    var people: [NSManagedObject] = []

    // Below is a computed property
    var appDelegate: AppDelegate {
        return UIApplication.shared.delegate as! AppDelegate
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // The below line is for giving a title to the View Controller.
        // title = "The List"

        searchBar.delegate = self

        tableView.register(UITableViewCell.self, forCellReuseIdentifier: "Cell")

        // The below line hides empty rows in a tableView
        tableView.tableFooterView = UIView()

    }

    //MARK: - IBAction addName implementation
    @IBAction func addName(_ sender: UIBarButtonItem) {
        let alert = UIAlertController(title: "New Name", message: "Add a new name", preferredStyle: .alert)
        let saveAction = UIAlertAction (title: "Save", style: .default) {
            [unowned self] action in
            guard let textField = alert.textFields?.first, let nameToSave = textField.text else {
                return
            }
            self.save(name: nameToSave)
            self.tableView.reloadData() // this is to reload the table data
        }

        let cancelAction = UIAlertAction(title: "Cancel", style: .cancel)

        // The below code handles the validation operation. In this case, we are checking wheather the field is empty and if it is 'save' button is disabled.
        alert.addTextField(configurationHandler: { (textField) in
            textField.text = ""
            textField.placeholder = "Enter something...."
            saveAction.isEnabled = false
            NotificationCenter.default.addObserver(forName: UITextField.textDidChangeNotification, object: textField, queue: OperationQueue.main) { (notification) in
                saveAction.isEnabled = textField.text!.count > 0
            }
        })

        alert.addAction(saveAction)
        alert.addAction(cancelAction)

        present(alert, animated: true)
    }

    // MARK: - SAVING TO CORE DATA

    // CoreData kicks in here!
    func save(name: String) {

        // 1
        let managedContext = appDelegate.persistentContainer.viewContext

        // 2
        let entity = NSEntityDescription.entity(forEntityName: "Person", in: managedContext)!
        let person = NSManagedObject(entity: entity, insertInto: managedContext)

        // 3
        person.setValue(name, forKeyPath: "name")

        // 4
        do {
            try managedContext.save()
            people.append(person)
        } catch let error as NSError {
            print("Could not save. \(error), \(error.userInfo)")
        }
    }

    // MARK: - FETCHING FROM CORE DATA

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

        // 1
        let managedContext = appDelegate.persistentContainer.viewContext

        // 2
        let fetchRequest = NSFetchRequest<NSManagedObject>(entityName: "Person")

        // 3
        do {
            people = try
                managedContext.fetch(fetchRequest)
        } catch let error as NSError {
            print("Could not save. \(error), \(error.userInfo)")
        }
    }

    // MARK: - searchBar functionality implementation

    func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
        if searchText != "" {
            var predicate: NSPredicate = NSPredicate()
            predicate = NSPredicate(format: "name contains[c] '\(searchText)'")
            let context = appDelegate.persistentContainer.viewContext
            let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Person")
            fetchRequest.predicate = predicate
            do {
                people = try context.fetch(fetchRequest) as! [NSManagedObject]
            } catch {
                print("Could not get search data!")
            }
        } else {
            let context = appDelegate.persistentContainer.viewContext
            let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Person")
            do {
                people = try context.fetch(fetchRequest) as! [NSManagedObject]
            } catch {
                print("Error in loading data.")
            }
        }
        tableView.reloadData() // This line reloads the table whether search is performed or not.
    }

    // This function closes the search bar when cancel button is tapped.
    func searchBarCancelButtonClicked(_ searchBar: UISearchBar) {
        searchBar.resignFirstResponder()
    }

    @IBAction func editButton(_ sender: Any) {
        tableView.isEditing = !tableView.isEditing

        // This switch case is for changing the title when editing
        switch tableView.isEditing {
        case true:
            editButton.title = "Done"
        case false:
            editButton.title = "Edit"
        }
    }

}

// MARK: - UITableViewDataSource
extension ViewController: UITableViewDataSource {

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return people.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let person = people[indexPath.row]
        let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath)
        cell.textLabel?.text = person.value(forKeyPath: "name") as? String
        return cell
    }

    // This function sets the height for a row programatically.
    func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
        return 55.0
    }

    // Determine whether a given row is eligible for reordering or not.
    func tableView(_ tableView: UITableView, canMoveRowAt indexPath: IndexPath) -> Bool {
        return true
    }

    // Process the row move. This means updating the data model to correct the item indices.
    func tableView(_ tableView: UITableView, moveRowAt sourceIndexPath: IndexPath, to destinationIndexPath: IndexPath) {
        let itemToMove =  people.remove(at: sourceIndexPath.row)
        people.insert(itemToMove, at: destinationIndexPath.row)
        tableView.reloadData()
    }

}

// MARK: - UITableViewDelegate
extension ViewController: UITableViewDelegate {

    func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
        return true
    }

    func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath) {
        if editingStyle == .delete {
            // handle delete (by removing the data from your array and updating the tableview)

            // MARK: - Delete the person from core data

            let person = people[indexPath.row]
            let managedContext = appDelegate.persistentContainer.viewContext
            managedContext.delete(person)
            try? managedContext.save() // This the short version of do-catch block used in above functions to save and fetch data

            // remove the person from cache / CoreData
            people.remove(at: indexPath.row)

            // delete row from table view
            tableView.deleteRows(at: [indexPath], with: .automatic)
        }
    }

}

任何帮助将不胜感激，因为我已经尝试了数周。

我的 CoreData 模型：

Answer 1

你的代码行：

var people: [NSManagedObject] = []

当然是问题的核心。 Core Data 不知道这个数组。删除该变量。您的表视图数据源应该从获取的结果控制器中获取其数据，如下所示：

let person = fetchedResultsController()?.object(at: indexPath) as? Person

您应该能够在教程like this one 或Apple 示例代码中找到许多工作UITableViewDataSource 代表的示例。遵循其中一个，让自己成为一个优秀的、传统的 table view 委托。上面这行代码来自little demo project which I forked recently。

另一个问题是Core Data 不会以任何特定顺序存储给定实体的托管对象。我在上一段中给出的链接都不支持排序。支持排序有两种选择：

备选方案 1. 使用 Core Data 有序关系。

如果您的 Persons 是某种 Group 实体的成员，则您的数据模型应该具有从 Group 到 Person 的一对多关系。您可以通过在 Data Model 检查器 中为这种关系打开 Ordered 复选框来使其成为有序关系。

备选方案 2. 使用 index 属性。

对于更简单的应用程序，并且这适用于当前在屏幕截图中的数据模型，您可以向您的 Person 实体添加诸如 index 属性之类的属性，并使您的获取结果控制器按此属性排序：

let sortDescriptor = NSSortDescriptor(key: "name", ascending: true)
fetchRequest.sortDescriptors = [sortDescriptor]
let frc = NSFetchedResultsController(fetchRequest: fetchRequest,
                             managedObjectContext: managedContext,
                               sectionNameKeyPath: nil,
                                        cacheName: nil)

其中我使用了您的符号名称managedContext。

Answer 2

添加属性“order” - Int16

func tableView(_ tableView: UITableView, moveRowAt sourceIndexPath: IndexPath, to destinationIndexPath: IndexPath) {
   if sourceIndexPath.row > destinationIndexPath.row {
        for i in destinationIndexPath.row..<sourceIndexPath.row {
            Items[i].setValue(i+1, forKey: "order")
        }

        Items[sourceIndexPath.row].setValue(destinationIndexPath.row, forKey: "order")
    }

    if sourceIndexPath.row < destinationIndexPath.row {
        for i in sourceIndexPath.row + 1...destinationIndexPath.row {
            Items[i].setValue(i-1, forKey: "order")
        }

        Items[sourceIndexPath.row].setValue(destinationIndexPath.row, forKey: "order")
    }

 //Save
}

加载

...

let orderSort = NSSortDescriptor(key: "order", ascending: true)
fetchRequest.sortDescriptors = [orderSort]

...