Swift overriding methods

Question

I'm so frustrated on searching what is the equivalent of this java code on swift:

public abstract class BaseApiSubscriber<T> extends Subscriber<T> {
   private WeakReference<MvpView> mvpViewWeakReference;
   private WeakReference<BasePresenter> basePresenterWeakReference;

   public BaseApiSubscriber(BasePresenter basePresenter, MvpView mvpView) {
     this.basePresenterWeakReference = new WeakReference<>(basePresenter);
     this.mvpViewWeakReference = new WeakReference<>(mvpView);
   }

   @Override
   public void onCompleted() {
   }

   @Override
   public void onError(Throwable e) {
      //handle generic errors here, call also the mvpView to handle generic responses on UI
   }

   @Override
   public void onNext(T t) {
   }

Basically here, I'm extending Subscriber so all of the generic response of API is handled on a single file. This works on my java (android), but I can't find how to make this work on swift. I tried searching about extensions, protocols but it seems they can't be extended. I did try to search, but I don't know the keyword for this, I try to code blindly (hoping it will work) but I can't. Maybe just a keyword, basic sample, or an explanation on this. Am I doing it right, right? Ready also for the downvotes because I just can't post a good code on swift. It is not even close to this.

Update: Somehow I got close to it, thanks to @luk2302, but then how can I implement this? Here's my code:

class BaseSubscriber: ObserverType {

typealias E = Response

func on(_ event: Event<Response>) {
    switch event {
    case .next(let _):
        print("Successing")
        break
    case .error(let error):
        print("Erorring")

        if let serviceError = error as? ServiceError {
            print("service error: " + serviceError.errorDescription!)
        }

        print(error)
        break
    case .completed:
        print("Completing")
        break
    }
}
}

Then I need to call this from here:

let base = BaseSubscriber()
repo.login(param: loginParam).subscribe(
     //Ive tried this:
     //base.on: {
     //}
     //but got an syntax error maybe hahahaha
)

What do you call this? So I can search and read about it. Thank you.

Update 2: Thanks to @Cristik, I've managed to do it, and by passing a closures, I can now pass methods to do specific task per request. My updated code:

func baseSubscriber<T>(mvpView: BaseMvpView, onNext: @escaping (T) -> Void, onError: @escaping (Error) -> Void, onCompleted: @escaping () -> Void)  -> (RxSwift.Event<T>) -> Void {
return { [weak mvpView] event in
    switch event {
    case let .next(element):
        mvpView?.hideLoading()
        print("super next")
        onNext(element)

    case .completed:
        mvpView?.hideLoading()
        print("super completed")
        onCompleted()

    case let .error(error):
        mvpView?.hideLoading()
        print("super error")
        if let serviceError = error as? ServiceError {
            print("Service error: \(serviceError.errorDescription ?? "Something wrong")")
        } else {
            onError(error)
        }
    }
}

}

But this is different to my approach on java in which I can override the onError() method so in case I want to disregard the generic error handling, I can do it. How can I apply it to swift?

Update 3:

BaseMvpView.swift

protocol BaseMvpView: class {

   func showLoading(message: String)

   func hideLoading()
}

BaseTableViewController.swift

class BaseTableViewController: UITableViewController, BaseMvpView {

var indicator: UIActivityIndicatorView?

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

override func viewDidLoad() {
    super.viewDidLoad()

    indicator = UIActivityIndicatorView(activityIndicatorStyle: UIActivityIndicatorViewStyle.gray)
    indicator?.frame = CGRect(origin: CGPoint.init(x: 0, y: 0), size: CGSize.init(width: 40, height: 40));
    indicator?.center = view.center
    view.addSubview(indicator!)
    indicator?.bringSubview(toFront: view)
    UIApplication.shared.isNetworkActivityIndicatorVisible = true
}

func showLoading(message: String) {
    indicator?.startAnimating()
}

func hideLoading() {
    indicator?.stopAnimating()
}
}

Answer 1

You don't need a dedicated class for this, seems the only thing you need is a subscriber that weakly references the view and the presenter, and that handles common event handling logic.

Since an RxSwift subscriber can also be a closure with one event argument, you could implement a free function that will create it:

func customSubscriber<T>(mvpView: MvpView, presenter: BasePresenter) -> (RxSwift.Event<T>) -> Void {
    return { [weak mvpView, weak presenter] event in
        switch event {
        case let .next(element):
            print("Received \(element)")

        case .completed:
             print("Done")

        case let .error(error):
            if let serviceError = error as? ServiceError {
                print("Service error: \(serviceError)")
            } else {
                print("Some error: \(error)")
            }
        }
    }
}

which you can use it like this:

myObserver.subscribe(customSubscriber(mvpView: someMvpView, presenter: somePresenter))

RxSwift paradigms are centered around closures: you create observers from closures, subscribers are closures, operators work with closures. Also in Swift other types like structs and enums (aka value types) are preferred over classes (aka reference types), they just work better in most of the contexts.

Update Based on the latest snippet, seems you also want to allow different event handling based on the receiver. This can be elegantly achieved by using a protocol with default implementations.

protocol Subscribable: class {
    associatedtype DataType

    func onNext(_ data: DataType)
    func onCompleted()
    func onError()
}

extension Subscribable where Self: BaseMvpView {
    func onNext(_ data: DataType) {
        hideLoading()
        print("super next")
    }

    func onCompleted() {
        hideLoading()
        print("super completed")
    }

    func onError() {
        hideLoading()
        print("super error")
        if let serviceError = error as? ServiceError {
            print("Service error: \(serviceError.errorDescription ?? "Something wrong")")
        }
    }
}

// BaseMvpView will get all above methos implemented, child classes can implement their own version.
extension BaseMvpView: Subscribable { 
    typealias DataType = DataTypeThatIsUsedByMvpView
}

// the subscriber function got simplifier as it no longer needs
// the callback parameters, as those are not part of the protocol
// this also makes the function more flexible as it's not tied to a
// concrete class
func baseSubscriber<S: Subscribable, T>(_ subscribable: S) -> (RxSwift.Event<T>) -> Void where S.DataType == T {
    return { [weak subscribable] event in
        switch event {
        case let .next(element):
            subscribable?.onNext(element)
        case .completed:
           subscribable.onCompleted()
        case let .error(error):
            subscribable.onError(error)
        }
    }
}

You can call the new function like this:

baseSubscriber(someMvpView)