Delegate between TableViewController and ViewController - ios

Question

I'm in my first week of developing in iOS and have become stuck on an issue with passing data between view controllers. My set up consists of a view with VC having a button in it and also a container view (no associated view controller). The container view has an embedded Segue to a TableView with TableViewController. The table has 6 rows and each row has a stepper that can change the value of a text view on the associated row. What I would like to do is collect the values of all the textviews when I press the button on the main view.
I am trying to use delegate to do this but when I press the button the returned value is always nil. I believe the problem is to do with the fact the VC is not being passed to the table view controller via the prepareForSegue function but I'm not sure why? Could be to do with the load order of the controllers?
import UIKit
class PredictionViewController: UIViewController, PredictionDelegate {
var predictionData: String!
#IBOutlet weak var messageTextBox: UITextView!
#IBOutlet weak var predictionSubmitButton: UIButton!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
self.messageTextBox.isEditable = false
}
override func viewDidAppear(_ animated: Bool) {
}
func prepareForSegue(segue: UIStoryboardSegue!, sender: AnyObject!) {
if (segue.identifier == "predictionSegue") {
// pass data to next view
let vc = segue.destination as! PredictionsTableViewController
vc.predictionHomeDelegate = self
}
}
func receiveData(with data: String) {
predictionData = data
print(predictionData)
}
#IBAction func predictionSubmitButtonAction(_ sender: UIButton) {
print(predictionData)
}
}
TableViewController: (stripped to minimum)
import UIKit
protocol PredictionDelegate: class {
func receiveData(with data: String)
}
class PredictionsTableViewController: UITableViewController, PredictionDelegate {
weak var predictionHomeDelegate: PredictionDelegate?
#IBOutlet weak var homeTeamScore1: UITextView!
#IBOutlet weak var homeTeamStepper1: UIStepper!
override func viewDidLoad() {
super.viewDidLoad()
}
override func viewDidAppear(_ animated: Bool) {
}
func getPredictionList() {
//does some stuff
self.passDataBackwards()
}
func receiveData(with data: String) {}
func passDataBackwards() {
let data = "{\"score\":\"1\"}"
predictionHomeDelegate?.receiveData(with: data)
}
#IBAction func homeTeamStepper1Action(_ sender: UIStepper) {
let score = Int(sender.value).description
homeTeamScore1.text = score
self.passDataBackwards()
}
}
Any help gratefully received!

Answer 1

Edit:
After comments...
You have the wrong idea about Protocols and Delegates. They are not needed here.
Instead, in your "home" VC, get a reference to the embedded VC. Then, add a function in your embedded VC that you can call to get its data.
// "home" view controller
class PredictionViewController: UIViewController {
// this will be a reference to the embedded view controller
var embeddedVC: PredictionsTableViewController?
#IBAction func getDataButtonTapped(_ sender: Any) {
if let tableData = embeddedVC?.getMyData() {
print("Result: \(tableData)")
}
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if (segue.identifier == "predictionSegue") {
if let vc = segue.destination as? PredictionsTableViewController {
// get a reference to the embedded VC
self.embeddedVC = vc
}
}
}
}
// embedded view controller
class PredictionsTableViewController: UIViewController {
var numTaps = 0
func getMyData() -> String {
return "\(numTaps)"
}
#IBAction func didTap(_ sender: Any) {
numTaps += 1
}
}
You're close, but a couple mistakes...
Here is a very, very simple example. View controller with container, which has a view controller with a button.
Code:
import UIKit
// your protocol
protocol PredictionDelegate: class {
func receiveData(with data: String)
}
// embedded view controller
// NOTE: this should NOT include PredictionDelegate
class PredictionsTableViewController: UIViewController {
weak var predictionHomeDelegate: PredictionDelegate?
#IBAction func didTap(_ sender: Any) {
// on button tap, "send data back"
predictionHomeDelegate?.receiveData(with: "Test")
}
}
// "home" view controller
// NOTE: this DOES include PredictionDelegate
class PredictionViewController: UIViewController, PredictionDelegate {
func receiveData(with data: String) {
print(data)
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if (segue.identifier == "predictionSegue") {
if let vc = segue.destination as? PredictionsTableViewController {
// set self as the delegate of the embedded PredictionsTableViewController
vc.predictionHomeDelegate = self
}
}
}
}
Notes:
Do NOT include func receiveData(with data: String) {} in your embedded view controller
Do NOT assign PredictionDelegate to your embedded view controller

Answer 2

You need to hook your segue to the vc itself instead of the cell and use
self.performSegue(withIdentifier: "predictionSegue", sender: nil)

Answer 3

Since these are two separate screens I am not too sure it makes too much sense to have the button on the first view controller that submits data from the second, can the button not just be on the second. If for whatever reason it can't you could pass the data back to the first view controller on segueing back by adding a public variable to the first view controller and adding another prepare method to the second to pass the data back like you have done when adding the delegate.