Save&Load Data locally in a persistent way using Realm

localRealmTableView.swift

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?


    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        window = UIWindow(frame: UIScreen.main.bounds)
        window?.rootViewController = UINavigationController(rootViewController: ViewController(style:.plain))
        window?.makeKeyAndVisible()
        return true
    }


}

//
//  ViewController.swift
//  ToDoWithRealm
//
//  Created by YOUNG on 30/08/2017.
//  Copyright © 2017 YOUNG. All rights reserved.
//  https://realm.io/docs/swift/latest/

import UIKit
import RealmSwift

final class TaskList: Object {
    @objc dynamic var text = ""
    @objc dynamic var id = ""
    let items = List<Task>()
    
    override static func primaryKey() -> String? {
        return "id"
    }
}

final class Task: Object {
    @objc dynamic var text = ""
    @objc dynamic var completed = false
}


class ViewController: UITableViewController {
    var items = List<Task>()
    var notificationToken: NotificationToken!
    var realm: Realm!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupUI()
        items.append(Task(value: ["text": "My First Task"]))
        setupRealm()
//        loadExistingTasks()
    }
    
    func setupUI() {
        title = "My Task"
        tableView.register(UITableViewCell.self, forCellReuseIdentifier: "cell")
        navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .add, target: self, action: #selector(add))
    }
    
    func setupRealm() {

        DispatchQueue.main.async {
            do {
                self.realm = try Realm()
                
                if self.realm.objects(TaskList.self).count == 0 {
                    try! self.realm.write {
                        self.realm.add(TaskList())
                    }
                    
                }
                
                func updateList() {
                    if self.items.realm == nil, let list = self.realm.objects(TaskList.self).first {
                        self.items = list.items
                    } else {
                        print("self.items.realm: \(self.items.realm)")
                        print("self.realm.objects(TaskList.self).count: \(self.realm.objects(TaskList.self).count)")
                        print("items not set")
                    }
                    self.tableView.reloadData()
                }
                updateList()

                self.notificationToken = self.realm.addNotificationBlock{ _,_  in updateList()}
            } catch {
                print("Couldn't load Realm")
            }
        }
    }
    
    func loadExistingTasks() {
        do {
            self.realm = try Realm()
            if self.items.realm == nil, let list = self.realm.objects(TaskList.self).first {
                self.items = list.items
            }
            self.tableView.reloadData()
        } catch {
            print("Couldn't load Realm")
        }
    }
    
    deinit {
        notificationToken.stop()
    }
    
    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return items.count
    }
    
    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
        let item = items[indexPath.row]
        cell.textLabel?.text = item.text
        cell.textLabel?.alpha = item.completed ? 0.5 : 1
        return cell
    }

    @objc func add() {
        let alertController = UIAlertController(title: "New Task", message: "Enter Task Name", preferredStyle: .alert)
        var alertTextField: UITextField!
        alertController.addTextField { textField in
            alertTextField = textField
            textField.placeholder = "Task Name"
        }
        alertController.addAction(UIAlertAction(title: "Add", style: .default) {
            _ in
            guard let text = alertTextField.text, !text.isEmpty else { return }
            
            let items = self.items
            try! items.realm?.write {
                items.insert(Task(value: ["text": text]), at: items.filter("completed = false").count)
            }
        })
        present(alertController, animated: true, completion: nil)
        
    }
}