swift couldn't store data back to array, even during seguing - ios

Question

I have two viewcontrollers, one is rootviewcontroller, the other one is selectorviewcontroller. In rootvc, there is a textfield and button, when the button is clicked, it takes us to the selectorvc where we can choose and if necessary add a new item (area) and then choose the item, after we choose it, it takes us back to the rootvc, and display the selected item in the textfield. I understand that if we don't use data persistence measures, the data added in won't persist after we recommence the app. Although I can add in new item to the selectorvc, but the newly added data just gone even after we unwind the segue back to rootvc and re-enter the selectorvc. I am not sure where I did wrong, as the data storing array is mutable. It is great if you could pointing me to the right direction. Thanks a lot.
A simple array is defined to store the data,
import UIKit
class AreaClass {
var areaName: String
init? (areaName: String) {
self.areaName = areaName
if areaName.isEmpty {
return nil
}
}
}
This is the unwind segue in the rootvc,
#IBAction func unwindWithSelectedArea(segue:UIStoryboardSegue) {
if let SelectorViewController = segue.sourceViewController as? SelectorViewController,
selectedArea = SelectorViewController.selectedArea
{
AreaSelectedTextField.text = selectedArea
}
}
This is the declaration and addnewitem in the selectorvc,
var selectedArea: String?
var selectedAreaIndex: Int?
var areas = [AreaClass]()
var newarea = AreaClass?()
override func viewDidLoad() {
super.viewDidLoad()
tableView.dataSource = self
tableView.delegate = self
areaNewnSelectedTF.delegate = self
saveButton.enabled = false
loadSample()
// Do any additional setup after loading the view.
}
func loadSample (){
let area1 = AreaClass(areaName: "TopHill")!
let area2 = AreaClass(areaName: "Foothill")!
let area3 = AreaClass(areaName: "Summit")!
let area4 = AreaClass(areaName: "Riverside")!
areas += [area1, area2, area3, area4]
}
#IBAction func addNewArea(sender: UIBarButtonItem) {
var dupli = false
if saveButton == sender {
let areaname = areaNewnSelectedTF.text ?? ""
newarea = AreaClass(areaName: areaname)
for var index = 0; index < areas.count; ++index {
if areaname == areas[index].areaName {
dupli = true
// Mark: alert for duplicate inputs
let alert = UIAlertController(title: "Duplicate", message: "Can't have same items", preferredStyle:.Alert)
alert.addAction(UIAlertAction(title: "OK", style: .Default, handler: nil))
presentViewController(alert, animated: true, completion: nil)
}
}
if dupli == false {
let newIndexPath = NSIndexPath(forRow: areas.count, inSection: 0)
areas.append(newarea!)
tableView.insertRowsAtIndexPaths([newIndexPath], withRowAnimation: .Bottom)
}
}
}
This is the PrepareforSegue in selectorvc
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if segue.identifier == "saveSelectionSegue" {
if let cell = sender as? UITableViewCell {
let indexPath = tableView.indexPathForCell(cell)
if let index = indexPath?.row {
selectedArea = areas[index].areaName
}
}
}
}

Answer 1

You need to use a delegate to pass data from a childViewController to your rootViewController.
Below there are ViewController(root) and SelectTableViewController(selector), they implement a simple example of what you look for. I used a struct to make it simple.
At first, you need to create a protocol using the role of your delegate => ViewControllerDelegate with a simple function with an argument "AreaStruct".
This protocol needs to be implemented by the "root". When you pressed the button, you performSegueWithIdentifier that will call prepareForSegue. In it, you pass yourself(ViewControllerDelegate) to the destinationViewController.
In your destinationViewController, the user select one row. By selecting, it triggers didSelectRowAtIndex. In it, you get the selectedArea (the concern AreaStruct) and with your delegate, you call choseArea(...). After that you pop the ViewController to go back to the root.
When you call choseArea, it will put the areaName into the label to display what you selected as shown by the implementation of choseArea(areaStruct : AreaStruct) in your RootViewController.(In this function, you can do whatever you want with your areaStruct)
------ EDIT ------
In your code, your "selectorviewcontroller" create the data => loadSample. So no matter what happened when you go to "selectorviewcontroller", you will always loadSample even if you added new "areas" before. I updated my example code based on your example.
ViewController -> press button -> SelectTableViewController -> add area -> select area -> back to ViewController
To summarise,
in ViewController, I setupListData when viewDidLoad is called
I pressed the button to go to SelectTableViewController
3 I passed myself(delegate) and dataList to SelectTableViewController in prepareForSegue
SelectTableViewController is loaded and display my list based on dataList !
I pressed addNewArea, it append a new area to "areas" that is only local to SelectTableViewController !
My list is refreshed and displays my new area
I select an area
I call the delegate by passing 2 arguments : What I selected and my updated areas(List); I pop SelectViewController => Popping SelectViewController, it disappear and all data are lost
When I called the delegate, I updated my label based on what I selected and also I updated dataList in ViewController with areas (from SelectTableViewController).
When I click on my button, see point 2.1. => You should understand
If you want to persist data, you could use different techniques such as singleton, core data, NSUserDefaults, etc.
ViewController.swift
import UIKit
import Foundation
struct AreaStruct {
var areaName : String
}
protocol ViewControllerDelegate : class{
func choseArea(areaStruct : AreaStruct, areas : [AreaStruct])
}
class ViewController: UIViewController, ViewControllerDelegate { //1. Implement the delegate here.
#IBOutlet weak var infoLabel: UILabel!
#IBOutlet weak var btnToVC: UIButton!
var dataList : [AreaStruct] = [AreaStruct]()
override func viewDidLoad() {
super.viewDidLoad()
self.setupListData()
}
func setupListData(){
for i in 0...5{
dataList.append(AreaStruct.init(areaName: "Coucou \(i)"))
}
}
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if segue.identifier == "SelectTableViewController" {
let destinationViewController = segue.destinationViewController as! SelectTableViewController
destinationViewController.delegate = self //2. Here you passed itself to the destinationViewController so it can know how to call you !
destinationViewController.areas = dataList //
}
}
func choseArea(areaStruct : AreaStruct, areas : [AreaStruct]) {
self.infoLabel.text = areaStruct.areaName
dataList = areas
}
#IBAction func pushToSelectTableViewController(sender: AnyObject) {
//0. When pressed, you want to go to SelectTableViewController
self.performSegueWithIdentifier("SelectTableViewController", sender: nil)
}
}
SelectTableViewController.swift
import UIKit
class SelectTableViewController: UITableViewController {
var areas : [AreaStruct] = [AreaStruct]()
weak var delegate : ViewControllerDelegate? // <-- Delegate to send a mess. to ViewController
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func addNewArea(sender: UIBarButtonItem) {
let hello_world = "Hello World" //For the example !
areas.append(AreaStruct.init(areaName: hello_world))
self.tableView.reloadData()
}
// MARK: - Table view data source
override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
return 1
}
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return areas.count
}
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("reuseIdentifier", forIndexPath: indexPath)
cell.textLabel?.text = areas[indexPath.row].areaName
return cell
}
override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
let selectedArea = areas[indexPath.row]
self.delegate?.choseArea(selectedArea, areas: areas) //3. When you select, you pass the data to ViewController via the delegate
self.navigationController?.popViewControllerAnimated(true)//4. You dismiss itself
}
}