why does my array overwrite itself every time i change view and go back to it - swift 3

Question

So I have two viewControllers. One contains tableView to display data from an array. second viewController is used to add stuff in an array.

here is my viewController file:

    import UIKit

    class ViewController: UIViewController {


        @IBOutlet weak var txtTitle: UITextField!

        @IBOutlet weak var txtLocation: UITextField!

        @IBOutlet weak var txtDate: UITextField!

        @IBOutlet weak var txtTime: UITextField!

        var eventsArray = [Event]()


        override func viewDidLoad() {
            super.viewDidLoad()
        }

        override func didReceiveMemoryWarning() {
            super.didReceiveMemoryWarning()
            // Dispose of any resources that can be recreated.
        }


        @IBAction func btnSave() {

            let newEvent = Event(eventTitle: txtTitle.text!, eventLocation: txtLocation.text!)

            eventsArray.append(newEvent)

            let savedEvents = NSKeyedArchiver.archivedData(withRootObject: eventsArray)

            UserDefaults.standard.set(savedEvents, forKey: "savedEvents")

            UserDefaults.standard.synchronize()   
        }

Here is my tableView:

import UIKit

class EventsTable: UIViewController, UITableViewDataSource, UITableViewDelegate{

    //var tableData = ViewController()

    var events = [Event]()

    @IBOutlet weak var table: UITableView!

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        // #warning Incomplete implementation, return the number of rows
        return events.count
    }


    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

        let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath) as! CustomeCell

        cell.title.text = events[indexPath.row].title

        cell.location.text = events[indexPath.row].location

        return cell

    }


    func retriveData(){
        if let data = UserDefaults.standard.object(forKey: "savedEvents") as? Data {

            if let storedData = NSKeyedUnarchiver.unarchiveObject(with: data) as? [Event]{
                events = storedData
            }

        }
    }

    override func viewDidAppear(_ animated: Bool) {

        retriveData()

        table.reloadData()

    }
}

Here is my UI: main.storyboard

Now, every time i add an event and go back to my tableView, it only shows the title in the cell even though i have custom cell set up (that's one of the issue). Other issue, the main one, is that if i go back to my viewController to add another event, it adds it BUT it overwrites the old array and it shows the latest event i added and replaces the old one and only shows the new event I added in the tableView. I have no clue what is going on here. I have a feeling that every time I hit "Save" button it creates a new array?

I have only implemented eventTitle and eventLocation so far.

Here is the link to my project if y'all having trouble understanding what i mean https://mega.nz/#!XBxU1Q5J!cAhpRrZJo7an4ab8HmD1HtH7GSisScKOGoykGm9orJo

Answer 1

Archiving the data and retrieving the archived data will have different memory references. And if you save again it will replace the old one.

And playing with app's sandbox frequently will be expensive process.

• Ideally you have to initialize an array in TableViewController class.
• Pass this array reference to ViewController.
• Add/Edit/Delete object in the same array.

• Go back to TableViewController and refresh the table view.

• General rule is to have the same reference of an array in both the controllers and save/retrieve it in-out of app's sandbox when required.

Now the point to save and retrieve you can do it in either way as below:

1. Manually: Keep a button to save the array in app sandbox. And retrieve it when you want.

2. Save the array in AppDelegate's didEnterInBackground method and retrieve it in foreGround method. You need to have some mechanism to get the reference of the eventArray in AppDelegate.

Hope this would be helpful!