【发布时间】：2020-07-31 08:28:38
【问题描述】：
对不起，如果已经有一个关于它的线程但被卡住了一段时间。
我对 CoreData 有点陌生（只知道如何持久化和获取项目），我正在尝试在我的应用程序中进行一个小查询，该查询将仅加载具有 isDone 属性 =“True”的那些。
问题是我不知道如何使用 NSFetchRequest 和 NSPredicate 所以我有点卡住了，希望你们能帮助我一些提示
import Foundation
import CoreData
import UIKit
import SwipeCellKit
class TasksManViewController: UITableViewController, SwipeTableViewCellDelegate {
@IBOutlet weak var Sege: UISegmentedControl!
let isSwipeRightEnabled = true
var tasksArray = [Task](){
didSet {
// because we perform this operation on the main thread, it is safe
DispatchQueue.main.async {
self.tableView.reloadData()
}
}
}
var doneTasksArr = [Task]() // an array of what to disply.
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
override func viewDidLoad() {
}
override func viewWillAppear(_ animated: Bool) {
loadTasks()
}
// MARK: - DataSource + Delegate Methods:
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return tasksArray.count
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "taskCellRow") as! SwipeTableViewCell
cell.delegate = self
cell.textLabel?.text = tasksArray[indexPath.row].title
return cell
}
func tableView(_ tableView: UITableView, editActionsForRowAt indexPath: IndexPath, for orientation: SwipeActionsOrientation) -> [SwipeAction]? {
if orientation == .left {
guard isSwipeRightEnabled else { return nil }
let doneAction = SwipeAction(style: .destructive, title: "Done") { (action, indexPath) in
//STEP1: Append the task to the doneTasksArr:
self.tasksArray[indexPath.row].isDone = true
self.doneTasksArr.append(self.tasksArray[indexPath.row])
//STEP2: Delete the task from the tasksArray since it was done.
self.context.delete(self.tasksArray[indexPath.row])
//STEP3: Remove the Row:
self.tasksArray.remove(at: indexPath.row)
//STEP4: Update the Model:
self.saveTasks()
self.tableView.reloadData()
}
//configure btn:
doneAction.backgroundColor = .cyan
return [doneAction]
} else {
let deleteAction = SwipeAction(style: .destructive, title: "Delete") { action, indexPath in
self.context.delete(self.tasksArray[indexPath.row])
self.tasksArray.remove(at: indexPath.row)
self.saveTasks()
self.tableView.reloadData()
}
return [deleteAction]
}
}
override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
tableView.deselectRow(at: indexPath, animated: true)
}
// MARK: - Class Methods:
@IBAction func addBtnTapped(_ sender: UIBarButtonItem) {
insertNewTask()
}
func insertNewTask() {
var textField = UITextField()
let alert = UIAlertController(title: "New Task", message: "Please Add Your Task", preferredStyle: .alert)
alert.addTextField { (alertTextField) in
alertTextField.placeholder = "Create New Task"
textField = alertTextField
}
let action = UIAlertAction(title: "Add", style: .default) { (action) in
let newItem = Task(context: self.context)
newItem.title = textField.text!
newItem.isDone = false
self.tasksArray.append(newItem)
self.saveTasks()
self.tableView.reloadData()
}
alert.addAction(action)
self.present(alert, animated: true, completion: nil)
}
// MARK: - Sege Section:
@IBAction func segeControlTapped(_ sender: UISegmentedControl) {
switch Sege.selectedSegmentIndex
{
case 0:
//Loading normal tasks which not done
loadTasks()
case 1:
//Loading the doneTasks:
loadDoneTasksFrom()
default:
print("There's something wrong with Sege!")
}
tableView.reloadData()
}
//MARK: - Model Manipulation Methods:
func saveTasks() {
do {
try! context.save()
} catch {
print("Error Saving context \(error)")
}
}
func loadTasks() {
let request: NSFetchRequest<Task> = Task.fetchRequest()
do{
tasksArray = try! context.fetch(request)
} catch {
print("There was an error with loading items \(error)")
}
}
func loadDoneTasksFrom() {
let request: NSFetchRequest<Task> = Task.fetchRequest()
request.predicate = NSPredicate(format: "isDone == %@", "true")
request.sortDescriptors = [NSSortDescriptor(key: "isDone", ascending: false)]
do{
tasksArray = try context.fetch(request)
} catch {
print("Error fetching data from context\(error)")
}
tableView.reloadData()
}
}
【问题讨论】：