为什么UserDefaults.standard.set不能保存我的数组？ 从后台删除应用程序后，数据将被清除

Question

I'm currently working on a calendar within my application I'm writing using Swift. Although it works correctly in that data (event logs) can be entered and added to an array which will show up within a table view, once the application is closed down and removed from the background, when I re-open it, the event logs are gone.

Have I made any mistakes in my code?

import UIKit
import JTAppleCalendar
var event = [String]()
var userData = false

class CalendarViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {

@IBOutlet weak var calendarView: JTAppleCalendarView!
@IBOutlet weak var monthAndYear: UILabel!
@IBOutlet weak var eventTable: UITableView!

override func viewDidAppear(_ animated: Bool) {
    eventTable.reloadData()
}

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

    userData = UserDefaults.standard.bool(forKey: "userData")

    if userData == true {
        UserDefaults.standard.object(forKey: "event")  //gets
    }

    else
    {
        event.append("NO USER DATA")
        UserDefaults.standard.set(event, forKey: "event")

        if event[0] == "NO USER DATA" {
            event.remove(at: 0)
            UserDefaults.standard.set(event, forKey: "event")
        }
    }
    eventTable.reloadData()
        }

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return event.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = UITableViewCell(style: UITableViewCellStyle.default, reuseIdentifier: nil)
    cell.textLabel?.text = event[indexPath.row]
    return cell
}
func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCellEditingStyle, forRowAt indexPath: IndexPath) {
    if editingStyle == UITableViewCellEditingStyle.delete
    {
        event.remove(at: indexPath.row)
        UserDefaults.standard.set(event, forKey: "event")
    }
    eventTable.reloadData()
}

Incase it's necessary here's the code which allows data to be entered in the array:

class AddEventViewController: UIViewController {

@IBOutlet weak var eventText: UITextField!
@IBAction func addEvent(_ sender: Any) {

    userData = true
    UserDefaults.standard.set(userData, forKey: "userData")

    if eventText.text == ""
    {
    }
    else
    {
        event.append(eventText.text!)
        UserDefaults.standard.set(event, forKey: "event")
    }
}

I've tried using the simulator and a real iOS devise along with re-installing Xcode, because I've read that it may be a problem with Xcode itself. I've also tried adding UserDefaults.standard.synchronize() all over the place, however, nothing seems to work.

Answer 1

The only line in your code that gets the value out of the UserDefaults is...

UserDefaults.standard.object(forKey: "event")

This doesn't actually do anything with that value. It gets it... and then throws it away.

This will make it look like it isn't being saved.

Change it to ...

event = UserDefaults.standard.object(forKey: "event")

Answer 2

调用set后需要调用synchronize()以保存更改

UserDefaults.standard.synchronize()