无法使用 Core Data 和 Swift 在表视图中正确保存和显示数据

Question

Goal:

My goal is to pass the current minimum, average and maximum value data to table view and present them to the user.

Error:

When I hit the "Save" button "nan" value is passed with the current minimum, average and maximum value data.

UI screenshot

Here is the table view before pressing the Save button

Here is the table view after pressing the Save button

Here is the current code:

Record.swift

import Foundation
import CoreData

class Record: NSManagedObject {
    var minimumValue: Float = .nan
    var averageValue: Float = .nan
    var maximumValue: Float = .nan
}

RecordTableViewController.swift

class RecordCell: UITableViewCell {
    @IBOutlet weak var maximumValueLabel: UILabel!
    @IBOutlet weak var averageValueLabel: UILabel!
    @IBOutlet weak var minimumValueLabel: UILabel!
}

class RecordTableViewController: UITableViewController, NSFetchedResultsControllerDelegate {

    private lazy var fetchedResultsController: NSFetchedResultsController = { () -> NSFetchedResultsController<NSFetchRequestResult> in
        let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "History")
        let sortDescriptor: [NSSortDescriptor] = []
        fetchRequest.sortDescriptors = sortDescriptor

        let appDelegate = UIApplication.shared.delegate as! AppDelegate
        let managedObjectContext = appDelegate.persistentContainer.viewContext

        let fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: managedObjectContext, sectionNameKeyPath: nil, cacheName: nil)
        return fetchedResultsController
    }()

    let cellIdentifier: String = "cellID"
    var recordsArray = [Record]()

    override func viewDidLoad() {
        super.viewDidLoad()

        let swipe = UISwipeGestureRecognizer(target: self, action: #selector(swipeRight(_:)))
        swipe.direction = .right
        self.view.addGestureRecognizer(swipe)

        recordsArray = fetchAllRecords()
    }

    override func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath) {
        switch editingStyle {
        case .delete:
            let removedRecord = fetchedResultsController.object(at: indexPath) as! NSManagedObject
            let context = fetchedResultsController.managedObjectContext
            context.delete(removedRecord)

            do {
                try context.save()
                self.recordsArray.remove(at: indexPath.row)
                tableView.deleteRows(at: [indexPath], with: .fade)
            } catch _ {

            }
        default:
            break
        }
    }
}

extension RecordTableViewController {
    public func fetchAllRecords() -> [Record] {
        let appDelegate = UIApplication.shared.delegate as! AppDelegate
        let context = appDelegate.persistentContainer.viewContext
        let request = NSFetchRequest<NSFetchRequestResult>(entityName: "History")
        request.returnsObjectsAsFaults = false

        do {
            let result = try context.fetch(request)
            return result as! [Record]
        } catch let error {
            fatalError(error.localizedDescription)
        }
    }
}

MainViewController.swift

import UIKit
import Dispatch
import CoreData
import Accelerate
import Foundation
import UserNotifications

class MainViewController: UIViewController {

    var minimum: Float = .nan
    var average: Float = .nan
    var maximum: Float = .nan
    var decibel: Float = .nan

    /// MARK: Segue functions

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "saveRecord" {
            let recordVC = segue.destination as! RecordTableViewController
            let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
            let record = Record.init(entity: NSEntityDescription.entity(forEntityName: "History", in: context)!, insertInto: context)

            record.minimumValue = Float(minDbLabel.text!) ?? 0.0
            record.averageValue = Float(averageDbLabel.text!) ?? 0.0
            record.maximumValue = Float(maximumDbLabel.text!) ?? 0.0

            saveNewRecord(record: record)

            self.recordsArray.append(record)
            recordVC.recordsArray = self.recordsArray
        }
    }

    @IBAction func save(_ sender: UIButton){
        self.performSegue(withIdentifier: "saveRecord", sender: nil)
    }

    // MARK: Core Data functions

    private func saveNewRecord(record: Record) {
        let appDelegate = UIApplication.shared.delegate as! AppDelegate
        let context = appDelegate.persistentContainer.viewContext

        var index: Int = 0

        let entity = NSEntityDescription.entity(forEntityName: "History", in: context)
        let newRecord = [NSManagedObject(entity: entity!, insertInto: context)] as [NSManagedObject]

        newRecord[index].setValue(record.minimumValue, forKey: "minimumValue")
        newRecord[index].setValue(record.averageValue, forKey: "averageValue")
        newRecord[index].setValue(record.maximumValue, forKey: "maximumValue")
        index += 1

        do {
            try context.save()
        } catch let error {
            print("\(error.localizedDescription)")
        }
    }
}

Any help is appreciated.

Answer 1

The code you provided is kinda confusing, however, here's how I setup my CoreData applications.

First: I create a CoreDataManager model
This will handle all of my Model functions like fetching viewing and context etc...

struct CoreDataManager {
  static let shared = CoreDataManager()

  let persistentContainer: NSPersistentContainer = {
    let perCon = NSPersistentContainer(name: "EntityName")
    perCon.loadPersistentStores { (storeDescription, err) in
      if let err = err {
        fatalError("\(err)")
      }
    }
    return perCon
  }()

  func fetchEntitys() -> [Entity] {
    let context = persistentContainer.viewContext
    let fetchRequest = NSFetchRequest<Entity>(entityName: "EntityName")
    do {
      let entity = try context.fetch(fetchRequest)
      return entity
    } catch let err {
      print("\(err)")
      return []
    }
  }

  func resetEntitys() {
    let context = persistentContainer.viewContext
    let batchRequest = NSBatchDeleteRequest(fetchRequest: Entity.fetchRequest())
    do {
      try context.execute(batchRequest)
    } catch let err {
      print("\(err)")
    }
  }
}

Second: Setup your secondViewController the viewController in which you create the objects in

1. You would need to create a delegate for this viewController

protocol CreateControllerDelegate: class {
  func didAdd(entity: Entity)
}

2. In your secondViewController in this case, it's CreateController you should add the following property.

weak var delegate: CreateControllerDelegate?

3. Implement the function in which you will save objects into your CoreData.

  func createEntity() {
    let context = CoreDataManager.shared.persistentContainer.viewContext
    let entity = NSEntityDescription.insertNewObject(forEntityName: "EntityName", into: context)
    entity.setValue(nameTextField.text, forKey: "name") 
    // set all of your values that you want to be saved.
    do {
      try context.save()
      dismiss(animated: true) {
        self.delegate?.didAdd(entity: entity as! Entity)
      }
    } catch {
      let nserror = error as NSError
      fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
    }
  }

Finally, setup your firstViewController the one in which you will display all of your Core Data objects.

1. Add a property to your MainController in which it will hold all of your Entity objects.

var objectsArray = [Entity]()

2. Inside of your MainController's viewDidLoad function add the following.

  override func viewDidLoad() {
    super.viewDidLoad()
    self.objectsArray = CoreDataManager.shared.fetchEntitys()
  }

3. Confirm and implement the CreateControllerDelegate in your MainController.

extension MainController: CreateControllerDelegate {
  func didAdd(entity: Entity) {
    objectsArray.append(entity)
    let indexPath = IndexPath(row: objectsArray.count - 1, section: 0)
    tableView.insertRows(at: [indexPath], with: .automatic)
  }
}

4. Push your secondViewController. I don't use Segues.

  @IBAction func handleAdd(_ sender: Any) {
    let createController = storyboard?.instantiateViewController(withIdentifier: "CreateController") as! CreateController
    createController.delegate = self
    let navController = UINavigationController(rootViewController: createController)
    navController.modalPresentationStyle = .fullScreen
    present(navController, animated: true)
  }

I hope this is helpful and if there's something that's not working let me know!

Good Luck!