Use Case with 2 ways for the same action

Question

Question 1: What is the correct way to build a Use Case (or more than one) with 2 ways to do the same action?

For example:

I have a 3 screens in

Answer 1

Question 1: What is the correct way to build a Use Case (or more than one) with 2 ways to do the same action?

In VIPER design, you can create two methods in the same Interactor suitable for each primary and alternates of the use case.

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Question 2: (Based on bhavik's answer) So I don't need one presenter for one interactor precisely, I can have 1 interactor and 3 presenters/views.

Based on our discussion and your updates, I think I understand it better.

• Presenter/View should not interact with more than on Interactor.
• Presenter/View may not interact with any Interactor at all as in case of CameraView.
• They are intermediate views as in Wizards.
• Multiple Presenter/View can interact with single Interactor.
• Interactor does not bind to any Presenter.
• Single Interactor is responsible for single use case and all of its alternate flows. 1-1 relationship.

So, you should have single EditPlacePresenter/View for EditPlaceInteractor that pass data Place data with or without Photo.

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Question 3: Should my boundary methods for the interactor always return void?

In bhavik's example they are returning something, but in the VIPER blog and the uncle Bob's video they always return void and the result comes in the form of another boundary method that the interactor calls on the presenter/controller.

I think you are referring to the below Presenter method that receives results from the Interactor.

- (void)foundUpcomingItems:(NSArray*)upcomingItems

For the above to work, the Interactor will have delegate instances that will be wired/patched through by the Presenter/Controller looking for result or data. This means the Presenter/Controller is tied to Interactor or their reference or return-function-pointer is passed in each Interactor method call. Is that by design?

I think, Interactor should return data as per the use case. For example Interactor should return the EditPlaceResult with success or failure.

• If success, it should include saved data, for example Place ID.
• If failed, should include fail reason.

This should be part of the use case. If not then, it should not return anything. It will return void and a separate Interactor will be queried by Presenter to check if Map Place was added successfully or not.

References in the blog:

• Presenter contains view logic for preparing content for display as received from the Interactor.
• Its up to the Presenter to take the data returned by the Interactor and format it for presentation.
• The Presenter receives results from an Interactor and converts the results into a form that is efficient to display in a View.

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Question 4: The VIPER way does not use a controller, only a presenter to talk to the interactor, when the uncle Bob's video uses a controller and a presenter for different interactions with the interactor. Which approach should I take?

You need to define VIPER routes for following navigation:

• Camera Button: Navigate from MapView to CameraView (Use Location)
• Long Press: Navigate from MapView to EditPlaceView (Use Coordinate)
• Photo taken: Navigate from CameraView to EditPlaceView
• Save Place: Send Interactor a request to Save Place with/without Photo as the case may be and jump back to MapView if successful
• Back Button: Back to previous View based on Navigation Stack

As per the VIPER blog, view controllers and navigation controllers are used by Presenters and Wireframes.

VIPER Wireframe handles Navigation and makes view controllers become lean, mean, view controlling machines.

Basically Wireframe abstracts away navigation controller and instead provides route definition.

Wireframe

• Owns UINavigationController and UIViewController
• Responsible for creating a View/ViewController and installing it in the window
• Routing are defined in Wireframes and contains navigation logic for describing which screens are shown in which order

Presenter

• Uses Wireframe to perform the navigation
• To keep view controllers lean, VIPER need to give View Controllers a way to inform interested parties when a user takes certain actions - Presenters come here!
• The view controller shouldn't be making decisions based on these actions, but it should pass these events along to something that can - Presenters should be making decisions!

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Question 5: If my Use Case is something like "Go to other screen", should it even have an interactor? Since the current view will tell its presenter what button was pressed (what view to go to) and this current presenter will tell its wireframe "change to this other wireframe".

No. Navigation as part of use case may not need Interactor. It is transition only. The target Presenter may need an Interactor. For example, CameraView/Presenter does not need Interactor but EditPlaceView needs to save the place.

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Overall: The idea behind architectural patterns is to divide a given software application into interconnected parts, so as to separate internal representations of information from the ways that information is presented to or accepted from the user. MVC, MVP, MVVM, VIPER all focus on isolating View, Logic and Navigation in one way or other.

Architectural patterns are limited in what they intend to decompose. We have to understand that architectural patterns do not decompose or isolate everything. Also if one architectural pattern delegates certain responsibilities to certain part, other does not do that at all probably or assign multiple responsibilities to single part.

We are allowed to extend or limit the isolation and decomposition to the extent that it justifies the cause and does not impose unnecessary separation of concerns that overrun the cost. You can choose to use navigation controllers and your presenter can take dependency on them without Wireframe routes defined. These controllers then will be responsible for the navigation between screens.