Passing an array using protocols/delegates - swift3

Question

I have tried over and over to get this to work, but to no avail. I am trying to pass an array from a SendingVC to a ReceivingVC and display the content of that array in two labels.
SendingVC Code:
import UIKit
protocol SenderVCDelegate {
func passArrayData(data: [String])
}
class SendingVC: UIViewController {
// DELEGATE
var delegate: SenderVCDelegate?
var carDetails: [String]? = ["BMW", "X5"]
override func viewDidLoad() {
super.viewDidLoad()
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
#IBAction func unwindToFirst(segue: UIStoryboardSegue) {
//
}
override func shouldPerformSegue(withIdentifier identifier: String, sender: Any?) -> Bool {
if (carDetails?.isEmpty)! {
return false
} else {
if let delegate = delegate, let data = carDetails {
delegate.passArrayData(data: data)
print("from inside segue: \(data)")
}
return true
}
}
}
ReceivingVC Code
import UIKit
class ReceivingVC: UIViewController, SenderVCDelegate {
#IBOutlet weak var lbl01: UILabel!
#IBOutlet weak var lbl02: UILabel!
var incomingCarDetails: [String] = []
override func viewDidLoad() {
super.viewDidLoad()
print("from inside viewLoad: \(incomingCarDetails)")
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?){
if let sendingVC: SendingVC = segue.destination as? SendingVC {
sendingVC.delegate = self
}
}
func passArrayData(data: [String]) {
incomingCarDetails = data
populateLabels(array: incomingCarDetails)
}
func populateLabels(array: [String]) {
for (index, value) in array.enumerated() {
switch index {
case 0:
lbl01.text = value
case 1:
lbl02.text = value
default:
break
}
}
}
}
Any help would be appreciated! :)
Thanks!

Answer 1

You seem to have confusion around the role of a delegate and where it should be implemented. You don't need to use a delegate to pass data from SendingVC to RecevingVC, you can simply set the property on the destination view controller in prepareForSegue;
class SendingVC: UIViewController {
func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if let destVC = segue.destinationViewController as? ReceivingVC {
destVC.incomingCarDetails = self.carDetails
}
}
}
If you do want to use a delegate, then you will set the SendingVC instance as the delegate of your ReceivingVC in prepareForSegue and change your protocol so that the delegate method returns data, rather than accepts data:
protocol SenderVCDelegate {
func passArrayData() -> [String]
}
Then, you can implement the delegate method and set the delegate in prepareForSegue
class SendingVC: UIViewController, SenderVCDelegate {
func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if let destVC = segue.destinationViewController as? ReceivingVC {
destVC.senderDelegate = self
}
}
func passArrayData() -> [String] {
return self.carDetails
}
}
In ReceivingVC you can call the delegate method in viewWillAppear
class ReceivingVC: UIViewController {
var incomingCarDetails = [String]()
var senderDelegate: SenderVCDelegate?
override func viewWillAppear(animated: bool) {
super.viewWillAppear(animated)
if let incomingDetails = self.senderDelegate?.passArrayData() {
self.incomingCarDetails = incomingDetails
}
}
}
As you can see this is a whole lot more work and no benefit. A delegation pattern is typically used where you want to send data back and where the function call will happen at an unpredictable time, such as in response to a network operation completing or a user interaction.