Finding it difficult to pass data to separate viewController

Question

I have searched through the net for couple of hours now thought this would be an easy task, but things are not going as planned. This question is edited, some of great fella has given great answer but I am still struggling.

Here is the scenario, I have a viewControllerA which is always visible. There is a small button on top of this view, when I click it there comes viewControllerB as a static tableViewController. Its a slide view from left to right to be honest like other apps.

There is one section and couple of rows in the tableView, when I tap 4th row I present viewControllerC, there is a UISwitch button there. When I dismiss the viewControllerC, viewControllerA appear again. viewControllerB is my menu controller therefore its not my greater concern .Now I want to pass data from viewControllerC to viewControllerA. Here is my broken code:

for viewControllerC :

class viewControllerC: UIViewController {
 ..//
 @IBAction func switchTapped(_ sender: UISwitch) {
     let vc = viewControllerA()
     if sender.isOn == true {
         vc.state = true
     } else if sender.isOn == false {
         vc.state = false
     }   
  }
 ..//
}

for viewControllerA :

class viewControllerA: UIViewController, GMSMapViewDelegate {
  var state:Bool?
  ...//
  if self.state == true {
      self.mapView.isTrafficEnabled = true
    } else {
      self.mapView.isTrafficEnabled = false
   } 
}

But its not working an I know I am not heading to the right direction. As you can see from the example I want to send ture when UISwitch is on and false when its off from viewControllerC to viewControllerA. Some of the folks have suggested delegate method but I am still struggling. I was following this link , I think "Passing data backwards through the shared state of the app" section meets my criteria. Although I need help. Thanks in advance.

Answer 1

You can pass data with Delegate pattern, here's an idea:

import UIKit

// Make a delegate protocol
protocol ViewControllerBDelegate: class {
    func didTapSwitch(isOn: Bool)
}

class ViewControllerB: UIViewController {

    // Make a weak delegate reference in VC B
    weak var delegate: ViewControllerBDelegate?

    var state: Bool?

    // On action trigger delegate method:
    @IBAction func switchTapped(_ sender: UISwitch) {
        delegate?.didTapSwitch(isOn: sender.isOn)
    }

}

class ViewControllerA: UIViewController {

    var stateFromSwitch: Bool?
    // In this VC you are instantiating viewController B
    // ... code ...
    // set delegate: viewControllerB.delegate = self
}

// implement ViewControllerBDelegate
extension ViewControllerA: ViewControllerBDelegate {
    func didTapSwitch(isOn: Bool) {
        stateFromSwitch = isOn
    }
}

Answer 2

First of all when you initiate viewControllerA :

let vc = viewControllerA()

You are creating new instance of viewcontrol which doesn’t reference to your first view control.

You can pass data to viewcontrollers in different ways. You can use delage pattern or you can use unwind.

In delegate method first you define a class type protocol with a function definition for changing something in viewControllerA.

protocol ViewControllerBDelegate: class {
    func changeSwitch(toValue: Boolean)
}

Then in ViewControllerB you define a weak reference to delegate

weak var delegate: ViewControllerBDelegate?

Then you adopt this protocol on ViewControlA:

extension ViewControllerA: ViewControllerBDelegate {
    func changeSwitch(toValue: Boolean) {
         state = toValue
     }
}

When you want to present or push to ViewControllerB you should set this variable to self

let vc = ViewControllerB()
vc.delegate = self
present(vc, animated: true, completion: nil)
// or navigationController. pushViewController(vc, animated: true)

if you are using segue to navigate from one viewcontroller to another, you should set delegate variable in prepare(for segue, sender). Override this function in ViewControllerA

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "mySegue" , 
       let vc = segue.destination as? ViewControllerB {
        vc.delegate = self
    }
}

Then when switch value changed you can use delegate to change value in ViewControllerA

delegate?.changeSwitch(toValue: sender.isOn)

on wind let you pop or dismiss child viewcontrollers to a certain parent and then do something. You can read a full tutorial here

EDIT

for chain delegates you can pass a delegate to ViewController B, then pass the same delegate to ViewController C.

in view controller C you define the same type delegate

weak var delegate: ViewControllerBDelegate?

then in view controller B when you are navigating to view controller c you pass the same delegate

let vc = ViewControllerC()
vc.delegate = self.delegate
present(vc, animated: true, completion: nil)

EDIT 2

SWRevealViewController is different scenario. revealController have an property named frontViewController. which can be your ViewControllerA if you dont push any other controllers on reveal. handling it with frontViewController is tricky you should be sure if frontController is ViewControllerA.

so i suggest you use another method to communicate with ViewControllerA. you can use NotificationCenter.

extension Notification.Name {
    static let updateMap = Notification.Name("updateMap")
}

in ViewControllerA

override func viewDidLoad() {
    super.viewDidLoad()
    NotificationCenter.default.addObserver(self, selector: #selector(updateMap(_:)), name: .updateMap, object: nil )
}

@objc func updateMap(notification: NSNotification) {
  if let state = notification.userInfo?["state"] as? Bool {
      // do something with state
  }
}

and in ViewControllerC you post a notification when switch value is Changed:

let userInfoDic:[String: Bool] = ["state": sender.isOn]
  // post a notification
  NotificationCenter.default.post(name: .updateMap, object: nil, userInfo: userInfoDic)

if frontViewController in reveal is pushed again. reveal will initiate new ViewControllerA for frontViewController. in this scenario you have to set settings in UserDefault and in ViewControllerA read this settings.

using UserDefaults :

in ViewControllerC

UserDefaults.standard.setValue(sender.isOn, forKey: "mapState")

in ViewControllerA

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    let state = UserDefaults.standard.value(forKey: "mapState") ?? false
    self.mapView.isTrafficEnabled = state
}