Function Overriding in iOS - ios

Question

I have created BaseClassviewController and all my controllers are derived from this controller. I am doing the following steps:
Set custom delegate in BaseClassViewController.
Implement all function of protocol in BaseClassViewController.
Then I am pushing HomeController derived from BaseClassViewController.
Again I am pushing DetailController also derived from BaseClassViewController.
Now when delegate function is called I should get control in DetailController but I am getting control in HomeController.
So my question is why its not calling top controller at navigation i.e DetailController and is it possible to call delegate functions in both controllers?
P.S I am overriding delegate functions in all child controllers.
EDIT: After reading answers and comments I think I have not been clear that much so adding following code snippet.
In Helper Class:
#objc protocol SampleDelegate: class
{
#objc optional func shouldCallDelegateMethod()
}
class SampleHelper: NSObject
{
var sampleDelegate:SampleDelegate!
static var sharedInstance = SampleHelper()
//It is triggered
func triggerDelegateMethod()
{
sampleDelegate!.shouldCallDelegateMethod()
}
func apiCall()
{
let urlString = URL(string: "https://google.com")
if let url = urlString {
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
if error != nil {
print(error)
} else {
if let usableData = data {
self. triggerDelegateMethod()
}
}
}
task.resume()
}
}
}
In BaseClass
class BaseClassViewController: UIViewController,SampleDelegate{
override func viewDidLoad() {
super.viewDidLoad()
}
override func viewWillAppear(_ animated: Bool)
{
super.viewWillAppear(true)
SampleHelper.sharedInstance.delegate = self;
}
func shouldCallDelegateMethod()
{
//Override
}
}
In HomeController i.e 1st controller to be pushed
class HomeViewController: BaseClassViewController{
override func shouldCallDelegateMethod()
{
//
}
}
In DetailController i.e 2nd controller is pushed after HomeController from HomeController.
class DetailViewController: BaseClassViewController{
override func viewDidLoad()
{
super.viewDidLoad()
SampleHelper.sharedInstance.apiCall()
}
override func shouldCallDelegateMethod()
{
//
}
}
Now my question is when delegate is triggered from helper class it calls shouldCallDelegateMethod in HomeViewController but not in DetailViewController. But DetailViewController is at top of navigation array.
Also is there any possibility I can trigger same function in both controller at a time with delegate only?

Answer 1

In BaseClassviewController you should have a delegate variable/property.
In HomeController and DetailController you need to set that delegate variable/property to self if you want that class to be listening to the delegate callbacks.

Answer 2

The basic problem is that you are using delegate with a singleton.
Setting the delegate in viewWillAppear is not a good solution either. In short, when view controllers are being shown and hidden, the delegate on your singleton will changed all the time.
Don't use delegates with singletons. Use a completion callback. Otherwise you will keep running into problems.
func apiCall(onCompletion: (() -> Void)?) {
let urlString = URL(string: "https://google.com")
if let url = urlString {
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
if error != nil {
print(error)
} else if let usableData = data {
onCompletion?()
}
}
task.resume()
}
}
called as
SampleHelper.apiCall {
// do something
}

Answer 3

Edit 2
After you posted your code, i realize that you have used the singleton class for delegation.
Delegates allows an object to send a message to another object.
Answer for your query is "No". You can not trigger same function in both controller at a time with delegate.
If you really want to listen an event in both class at a time, i would suggest you to use NSNotificationCenter instead of delegate.

Answer 4

Thats not the correct way to achieve this. I think proper way to set delegate only in respective UIViewController rather than implementing that protocol on BaseViewController and then overriding in child classes. So your implementation should be like.
In HomeViewController
class HomeViewController: BaseClassViewController {
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(true)
SampleHelper.sharedInstance.delegate = self;
}
func shouldCallDelegateMethod() {
// Provide implementation
}
}
In DetailViewController
class DetailViewController: BaseClassViewController {
override func viewWillAppear(_ animated: Bool) {
super.viewDidLoad()
SampleHelper.sharedInstance.delegate = self;
}
func shouldCallDelegateMethod() {
// Provide implementation
}
}
Using this imeplementation you will be having only one-to-one communication design pattern, ensuring right UIViewController to be called.