The final word VIPER structure tutorial

Swift design patterns and iOS architectures

A software program design sample is mainly a generic template of remedy a selected – however normally native – scenario. Achitectural patterns have greater impression on the entire codebase, they’re excessive degree generic templates. Please keep in mind one factor:

there isn’t a such factor as a foul structure

The weapon of choise solely depends upon the scenario, however you understand every part is relative. Let’s stroll via all of the iOS design patterns and architectures actual fast and begin studying VIPER. 🐍

Swift design patterns

Let’s begin with the fundamentals, proper? If we do not get into UIKit, we are able to discover that there are lots of design patterns invented, perhaps you understand a few of them already. However hey, since we do not have that a lot time and I would like to speak about VIPER, let’s try the essential precept of constructing UIKit apps utilizing the MVC sample.

MVC

The Mannequin-View-Controller (Huge-View-Controller) sample is a primary idea. You have got normally an enormous UIViewController subclass that controls all of the views and collects each mannequin that wanted to be displayed for the tip consumer. For instance you name an API endpoint utilizing URLSession or Alamofire from the controller, do the response knowledge validation and formatting then you definitely implement your desk or assortment view delegates on the view controller, so mainly all the applying logic goes inside that single overstuffed depressing view controller class. Does this ring a bell for you? 🙄

MVVM

After realizing the issue, the very first thing that you are able to do is outsourcing the info reworking or binding half to a sepearate class. That is how the good folks at Miscrosoft invented the Mannequin-View-ViewModel structure sample. Now you are one step nearer, your knowledge fashions and the views can have their “get collectively” on an entire new degree inside shiny new recordsdata far-far away from controller land. Nonetheless this sample is not going to clear up all of the leftovers contained in the view controller. Keep in mind that you continue to should feed the view controller with knowledge, deal with all of the totally different states.

MVP

What if we transfer out all the info loading and presentation stuff from the view controller and put it into a brand new class magically known as the Presenter? Sounds good, the view controller can personal the brand new presenter occasion and we are able to reside fortunately ever after. C’mon folks we should always actually rename this to the Most Priceless Sample ever! 😉

The Coordinator sample

Say howdy to The coordinator by Soroush Khanlou. Or ought to I merely name this because the Inverse Mannequin View Presenter sample? Look, right here is the deal, coordinators are on an entire new degree inside this evolution progress, however additionally they have an excessive amount of to do. It is towards the Single Accountability precept, as a result of now you need to handle the presentation context, the info storage, the routing and all of the differnet states inside coordinators or sub-coordinators… however, lastly your view controller is free from all of the leftover baggage and it could actually focus immediately on it is job, which is? 🙃

To be fucking dumb.

Presenting views utilizing UIKit associated stuff, and forwarding occasions.

I do not hate the design patters from above, I am simply merely attempting to level out (in a humorous / sarcastic method) why VIPER was born on the primary place. 😅

Are you continue to with me? 😬

The VIPER structure

To start with DO NOT imagine that VIPER is dangerous, simply because somebody misused it. I believe it is a freaking wonderful structure! You simply should study it correctly, which is tough, due to the dearth of fine tutorials. Everyone seems to be evaluating architectures, however that is not what folks ought to do. So far as I can see, an MVP is nice for a small app with a number of screens, it is best to by no means use VIPER for these apps. The true drawback begins when you app grows and increasingly elements get into the sport.

If you’re planning to write down a small app, simply begin with MVC. Afterward you’ll be able to repair the huge view controller drawback with MVVM, however if you wish to take it one degree additional you’ll be able to all the time use MVP or the coordinator sample to maintain maintainability. Which is totally nice, till you understand sooner or later that your code is full of utility lessons, managers, handlers and all of the nonsense objects. Sounds acquainted? 😅

As I discussed this earlier than there isn’t a such factor as a foul structure. There are solely dangerous selections, which lead us to hardly maintainable codebases. So let me information you thru probably the most helpful design sample that you will ever need to know so as to write truely scalable iOS purposes: VIPER with module builders = VIPER(B)

Understanding VIPER

The VIPER structure relies on the only accountability precept (S.O.L.I.D.)) which leads us to the speculation of a clear structure. The core elements or to illustrate layers of a VIPERB module are the next ones:

View

It is the interface layer, which suggests UIKit recordsdata, largely UIViewController subclasses and all the opposite stuff. Views do not do something that is associated to enterprise logic, the’re only a presentation and occasion forwarding layer which is utilized by the presenter. As a result of the view is only a pure view controller, you should use MVVM ideas or knowledge managers to make your undertaking much more concise.

Interactor

The interactor is accountable for retrieving knowledge from the mannequin layer, and its implementation is totally impartial of the consumer interface. It is vital to do not forget that knowledge managers (community, database, sensor) will not be a part of VIPER, so they’re handled as separate elements (providers), coming outdoors from the VIPER module land and they are often injected as dependencies for interactors.

The Interactor can put together or remodel knowledge, that is coming from the service layer. For instance it could actually do some sorting or filtering earlier than asking the correct community service implementation to request or save the info. However do not forget that the Interactor doesn’t know the view, so it has no thought how the info needs to be ready for the view, that is the position of the Presenter. 🙄

Presenter

UIKit impartial class that prepares the info within the format required by the view and take selections primarily based on UI occasions from the view, that is why generally it is referred as an occasion handler. It is the core class of a VIPER module, as a result of it additionally communicates with the Interactor and calls the router for wire-framing (aka. to current a brand new module or dismiss the present one).

It is the one class that communicates with nearly all the opposite elements. That is the ONLY job of the presenter, so it shouldn’t know something about UIKit or low degree knowledge fashions. Mainly it is the guts of the applying, or some would say it is the place the place all of the enterprise logic will get carried out. 💜

Entity

Plain mannequin lessons used largely by the interactor. Normally I am defining them outdoors the VIPER module construction (within the service layer), as a result of these entities are shared throughout the system. We may separate them by module, however normally I do not like that strategy as a result of eg. all of the CoreData fashions will be generated into one place. Similar factor applies if you’re utilizing Swagger or an analogous device.

Router

The navigation logic of the applying utilizing UIKit lessons. For instance if you’re utilizing the identical iPhone views in a iPad utility, the one factor that may change is how the router builds up the construction. This lets you hold every part else, however the Router untouched. It additionally listens for navigation move modifications from the presenter, so it will show the correct display if wanted. Additionally if you want to open an exterior URL name UIApplication.shared.openURL(url) contained in the Router as a result of that is additionally a routing motion, the identical logic applies for social media sharing utilizing UIActivityViewController.

Additionally if you need to go knowledge between VIPER modules it appears like a proper place to do that within the router. I normally talk between two module utilizing a delegate sample, so I picked up this behavior of calling delegate capabilities within the router. 📲

Builder

Some individuals are utilizing the router to construct the entire module, however I do not like that strategy. That is why I am all the time utilizing a separate module builder class. It is solely accountability is to construct the whole module by utilizing dependency injection for all of the extenal providers. It could additionally construct mock or different variations of the identical module. That is fairly useful if it involves unit testing. Completely is smart. 👍

NOT every part is a VIPER module

For instance if you wish to create a generic subclass from a UIViewWhatever please do not attempt to stuff that into the elements above. You need to create a spot outdoors your VIPER modules folder and put it there. There will likely be some use circumstances with particular lessons which are higher to not be VIPERized! 😉

Companies and utility particular code

I normally have 3 separate layers in my purposes. Modules, providers, and app. All of the VIPER modules are sitting contained in the Modules folder. The whole lot that is community or knowledge associated goes to the Companies folder (api service, core knowledge service, location service, and so on.) and afterward will get used within the module builder relying the present atmosphere (for instance mock implementation for testing). All of the remaining stuff like view subclassess, and different UI associated objects, app particular styling or design sensible issues are positioned contained in the App listing.

Methods to write VIPER code?

I am unable to emphase sufficient how vital is to study this structure earlier than you begin utilizing it. I imagine that issues can go actual dangerous if somebody misunderstands VIPER and begin placing view logic in a presenter for instance. If you happen to had a earlier dangerous expertise with VIPER, take into consideration this quote: do not blame the device, blame the carpenter (simply as Ilya Puchka properly mentioned on a twitter dialog). 🔨

Each single part will simply get into the suitable place when you observe the principles of VIPER.

Module technology

By no means begin to create a VIPER module by hand, it is best to all the time use a code generator, as a result of (sadly) you may want a number of boilerplate code for every module. That appears fairly unlucky at first sight, however that is what offers the true energy of this structure. All members of your developer crew will know the place to search for if a particular challenge happens. If it is a view challenge, you need to repair the view, if it involves a navigation drawback then it is a router drawback.

There are a lot of present code generator options (one of many famoust is generamba), however I made my very own little Swift device for producing VIPER modules. It is fairly rattling light-weight, nevertheless it’s actually heplful (it makes use of templates so as to generate a brand new module) i am calling it: VIPERA. (Hungarian identify of the viper snake… haha 😂)

You simply should clone / obtain the repository & run swift run set up --with-templates so as to make it work. To any extent further you’ll be able to merely run vipera MyModule to generate a brand new module primarily based on the default template. As a second argument you’ll be able to go your individual template listing identify (you’ll be able to create your individual template below the ~/.vipera folder, or you’ll be able to change the default one too).

The anatomy of the bottom template is fairly easy, I am not creating subfolders for every layer, however I am separating the interfaces and the default implementation elsewhere. That offers me a bit little bit of sanity, as a result of many of the VIPER templates appeared to be very deterrent simply due to the undertaking construction.

Naming conventions

Protocols are outlined for nearly each VIPER part. Each protocol will likely be prefixed with the module identify, and it will not have some other suffix besides from the layer identify (like MyModuleRouter, MyModulePresenter).

Default implementation is used for the essential state of affairs, each protocol implementation follows the ModuleName+Default+Layer naming conference. So for instance MyModuleDefaultRouter or MyModuleDefaultPresenter.

Inter-module communication utilizing delegates

The move is one thing like this:

Router / Presenter

The presenter can ship occasions for the router utilizing the router protocol definition.

Presenter / Interactor

The interactor can notify the presenter via the presenter’s interface, and the presenter can name the interactor utilizing the outlined strategies contained in the interactor protocol.

Presenter / View

The view normally has setter strategies to replace it is contents outlined on the view protocol. It could additionally notify the presenter of incoming or load occasions via the presenter protocol.

Information switch between modules

Think about an inventory, you choose an merchandise and go to a brand new controller scene. You must go at the least a novel indentifier between VIPER modules to make this attainable.

It is normally completed considerably like this:

• The view calls the didSelect technique on the presenter with the id
• The presenter forwards the id to the router utilizing the routeFor(id) technique
• The router calls the builder to construct a brand new module utilizing the id
• The builder builds the brand new module utilizing the id
• The router presents the brand new module utilizing it is view (controller)
• The brand new module passes the id for everybody who wants it (router, presenter)
• The brand new module’s presenter will get the id
• The brand new module’s interactor masses the info and offers it for the presenter
• The brand new module’s presenter offers the info for the view and presents it
• Element display seems with correct knowledge.

If you’re presenting a controller modally you can too go the unique router as a delegate, so you’ll shut it correctly if it is wanted. 😎

Reminiscence administration

Lengthy story quick:

• The builder holds noone.
• The router retains a weak reference of the view and the presenter.
• The presenter holds the router and the interactor strongly
• The interactor retains a weak refernece of the presenter
• The view retains a powerful refernece of the presenter
• UIKit holds the views.

You need to verify this within the supplied instance, no leaks – I hope so – every part will get launched good and easily after you return or dismiss a module. 🤞

Remaining conclusion: ought to I study VIPER?

Though VIPER is very criticized due to it is complexity, all I can say it is definitely worth the effort to study its priciples correctly. You may see that there are far more advantages of utilizing VIPER as an alternative of ignoring it.

Benefits

• Simplicity – for giant groups on complicated tasks
• Scalability – simultaneous work seamlessly
• Reusability – decoupled app elements primarily based on roles
• Consistency – module skeletons, separation of considerations
• Readability – Single tasks (SOLID)
• Testability – separated small lessons, TDD, higher code protection
• Interfaces – module independence, properly outlined scopes
• Bug fixing – simpler to trace points, find bugs and issues
• Supply management – smaller recordsdata, much less conflicts, cleaner code
• Simple – codebase seems comparable, quicker to learn others work

Drawbacks

• Verbosity – many recordsdata per module
• Complexity – many protocols and delegates
• On-boarding – lack of correct VIPER information
• Engagement – VIPER is dangerous, as a result of it is complicated, meh!

I made a follow-up article about VIPER greatest practices that I’ve study alongside the journey, you could find the pattern repository on github. I hope that these tutorials will aid you to study this structure higher, when you have any questions, be happy to contact me on twitter. 👨‍💻