如何使用核心数据从上到下对表视图项目进行排序

Question

我正在尝试在表视图中创建一个名称列表，我从上到下对其进行排序，我正在使用coreData来保存所有信息，但是当我重新启动应用程序时，我的tableView是从下到上而不是从上到下排序的。

我尝试使用许多其他方法，但对此感到困惑。

我的核心数据条目"人"，里面有"名字"

import UIKit
import CoreData
var newList = [Person]()
var currentList = [Person]()
var myIndex = 0
class TableViewVC_SmartAccounting: UIViewController,UITableViewDataSource, UITableViewDelegate, UISearchBarDelegate, UITextFieldDelegate {
@IBOutlet weak var txtField: UITextField!
@IBOutlet weak var tableView: UITableView!
@IBOutlet weak var outAdd: UIButton!
@IBOutlet weak var searchBar: UISearchBar!
override func viewDidLoad() {
    super.viewDidLoad()
    fetchData()
    newList = currentList
    searchBar.backgroundImage = UIImage()
    txtField.returnKeyType = UIReturnKeyType.done
    txtField.delegate = self
}
override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
}

func textFieldShouldReturn(_ textField: UITextField) -> Bool {
    txtField.resignFirstResponder()
    print("RETURN")
    return true
}
func fetchData(){
    let fetchRequist: NSFetchRequest<Person> = Person.fetchRequest()
    do {
        let listFetched = try PersistenceService.context.fetch(fetchRequist)
        currentList = listFetched
        self.tableView.reloadData()
    } catch let err as NSError {
        print("Field to fetch an item", err)
    }
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return currentList.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath) as! TableViewCellVC_SmartAccounting
    cell.lblName.text = currentList[indexPath.row].name
    return cell
}
func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
    return true
}
func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath) {
    if editingStyle == .delete {
        let person = currentList.remove(at: indexPath.row)
        PersistenceService.context.delete(person)
        PersistenceService.saveContext()
        self.tableView.deleteRows(at: [indexPath], with: .fade)
    }
}
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    myIndex = indexPath.row
    performSegue(withIdentifier: "segue", sender: self)
    tableView.deselectRow(at: indexPath, animated: true)
}
func addPerson(){
    if txtField.text != ""{
        let person = Person(context: PersistenceService.context)
        person.name = txtField.text
        PersistenceService.saveContext()
       // currentList.append(person)
        currentList.insert(person, at: myIndex)
        view.endEditing(true)
        newList = currentList
        let indexPath = IndexPath(row: myIndex, section: 0)
        tableView.insertRows(at: [indexPath], with: .left)
       // tableView.insertRows(at: [IndexPath(row: list.count - 1, section: 0)], with: .automatic)
    }
    txtField.text = ""
    self.view.endEditing(true)

}
func setUpSearchBar() {
    searchBar.delegate = self
}
func searchBarSearchButtonClicked(_ searchBar: UISearchBar) {
    self.searchBar.endEditing(true)
}
func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
    guard !searchText.isEmpty else {currentList = newList
        tableView.reloadData()
        return }
    currentList = newList.filter ({ (Person) -> Bool in
        (Person.name?.lowercased().contains(searchText.lowercased()))!
    })
    tableView.reloadData()
}
func searchBar(_ searchBar: UISearchBar, selectedScopeButtonIndexDidChange selectedScope: Int) {
}
@IBAction func btnAdd(_ sender: Any) {
    addPerson()
}

}

Answer 1

• 在Person实体中添加类型为 Int32 的属性index

• 在控制器中添加一个方法来重新索引currentList并保存上下文

  func reindex()
  {
      for (index, person) in currentList.enumerated() {
          person.index = Int32(index)
      }
      PersistenceService.saveContext()
   }
  

• 在fetchData中添加排序描述符

  fetchRequist.sortDescriptors = [NSSortDescriptor(key: "index", ascending: true)] 
  

• 插入对象后，重新索引数组

  let person = Person(context: PersistenceService.context)
  person.name = txtField.text
  person.index = Int32(myIndex)
  currentList.insert(person, at: myIndex)
  let indexPath = IndexPath(row: myIndex, section: 0)
  tableView.insertRows(at: [indexPath], with: .left)
  reindex()
  view.endEditing(true)
  newList = currentList
  

• 删除对象后，也会对数组重新编制索引

  if editingStyle == .delete {
      let person = currentList.remove(at: indexPath.row)
      PersistenceService.context.delete(person)
      self.tableView.deleteRows(at: [indexPath], with: .fade)
      reindex()
  }