Swift design patterns and iOS architectures
A software program design sample is principally a generic template of tips on how to remedy a selected – however often native – state of affairs. Achitectural patterns have larger influence on the entire codebase, they’re excessive stage generic templates. Please keep in mind one factor:
there isn’t a such factor as a foul structure
The weapon of selection solely will depend on the state of affairs, however you recognize the whole lot is relative. Let’s stroll by 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 a lot of design patterns invented, perhaps you recognize a few of them already. However hey, since we do not have that a lot time and I might 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 fundamental idea. You have got often 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 principally all the appliance 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 remodeling or binding half to a separate class. That is how the sensible individuals at Microsoft 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 stage inside shiny new recordsdata far-far away from controller land. Nonetheless this sample won’t clear up all of the leftovers contained in the view controller. Do not forget that you continue to should feed the view controller with knowledge, deal with all of the completely 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 stay fortunately ever after. Come on individuals we must always actually rename this to the Most Helpful 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 stage inside this evolution progress, however in addition 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 completely different states inside coordinators or sub-coordinators… however, lastly your view controller is free from all of the leftover baggage and it may 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 approach) why VIPER was born on the primary place. 😅
Are you continue to with me? 😬
The VIPER structure
Initially DO NOT consider that VIPER is unhealthy, simply because somebody misused it. I believe it is a freaking wonderful structure! You simply should be taught it correctly, which is difficult, due to the dearth of fine tutorials. Everyone seems to be evaluating architectures, however that is not what individuals ought to do. So far as I can see, an MVP is nice for a small app with just a few screens, it’s best to by no means use VIPER for these apps. The actual drawback begins in case you app grows and increasingly more parts get into the sport.
In case you are planning to jot down a small app, simply begin with MVC. In a while you may repair the large view controller drawback with MVVM, however if you wish to take it one stage additional you may at all times use MVP or the coordinator sample to maintain maintainability. Which is totally positive, till you understand at some point that your code is filled with utility courses, 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 unhealthy selections, which lead us to hardly maintainable codebases. So let me information you thru essentially the most helpful design sample that you will ever wish to know in an effort to write really scalable iOS functions: VIPER with module builders = VIPER(B)
Understanding VIPER
The VIPER structure relies on the only duty precept (S.O.L.I.D.)) which leads us to the speculation of a clear structure. The core parts or as an example layers of a VIPERB module are the next ones:
View
It is the interface layer, which suggests UIKit recordsdata, principally UIViewController subclasses and all the opposite stuff. Views do not do something that is associated to enterprise logic, they’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 utilize MVVM ideas or knowledge managers to make your venture much more concise.
Interactor
The interactor is answerable for retrieving knowledge from the mannequin layer, and its implementation is totally impartial of the consumer interface. It is essential to keep in mind that knowledge managers (community, database, sensor) should not a part of VIPER, so they’re handled as separate parts (companies), coming exterior 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 may do some sorting or filtering earlier than asking the right community service implementation to request or save the info. However keep in mind that the Interactor would not know the view, so it has no concept how the info ought to be ready for the view, that is the function 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 typically 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 virtually all the opposite parts. That is the ONLY job of the presenter, so it mustn’t know something about UIKit or low stage knowledge fashions. Principally it is the guts of the appliance, or some would say it is the place the place all of the enterprise logic will get carried out. 💜
Entity
Plain mannequin courses used principally by the interactor. Normally I am defining them exterior the VIPER module construction (within the service layer), as a result of these entities are shared throughout the system. We might separate them by module, however often I do not like that strategy as a result of e.g. all of the CoreData fashions could be generated into one place. Identical factor applies in case you are utilizing Swagger or the same software.
Router
The navigation logic of the appliance utilizing UIKit courses. For instance in case you are utilizing the identical iPhone views in a iPad software, the one factor which may change is how the router builds up the construction. This lets you maintain the whole lot else, however the Router untouched. It additionally listens for navigation movement modifications from the presenter, so it will show the right display screen if wanted. Additionally if it’s essential 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 seems like a proper place to do that within the router. I often talk between two module utilizing a delegate sample, so I picked up this behavior of calling delegate features 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 at all times utilizing a separate module builder class. It is solely duty is to construct the whole module by utilizing dependency injection for all of the exterior companies. It may well additionally construct mock or different variations of the identical module. That is fairly useful if it involves unit testing. Completely is smart. 👍
NOT the whole lot 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 parts above. You need to create a spot exterior your VIPER modules folder and put it there. There might be some use instances with particular courses which are higher to not be VIPERized! 😉
Companies and software particular code
I often have 3 separate layers in my functions. Modules, companies, and app. All of the VIPER modules are sitting contained in the Modules folder. All the pieces that is community or knowledge associated goes to the Companies folder (API service, core knowledge service, location service, and many others.) 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 smart issues are positioned contained in the App listing.
Methods to write VIPER code?
I can not emphasize sufficient how essential is to be taught this structure earlier than you begin utilizing it. I consider that issues can go actual unhealthy if somebody misunderstands VIPER and begin placing view logic in a presenter for instance. When you had a earlier unhealthy expertise with VIPER, take into consideration this quote: do not blame the software, blame the carpenter (simply as Ilya Puchka properly mentioned on a twitter dialog). 🔨
Each single part will simply get into the best place in case you observe the foundations of VIPER.
Module era
By no means begin to create a VIPER module by hand, it’s best to at all times 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 group will know the place to search for if a particular problem happens. If it is a view problem, you need to repair the view, if it involves a navigation drawback then it is a router drawback.
There are various present code generator options (one of many well-known is Generamba), however I made my very own little Swift software for producing VIPER modules.
Naming conventions
Protocols are outlined for nearly each VIPER part. Each protocol might be prefixed with the module identify, and it will not have every other suffix besides from the layer identify (like MyModuleRouter, MyModulePresenter).
Default implementation is used for the essential situation, each protocol implementation follows the ModuleName+Default+Layer naming conference. So for instance MyModuleDefaultRouter or MyModuleDefaultPresenter.
Inter-module communication utilizing delegates
The movement 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 by the presenter’s interface, and the presenter can name the interactor utilizing the outlined strategies contained in the interactor protocol.
Presenter / View
The view often has setter strategies to replace it is contents outlined on the view protocol. It may well additionally notify the presenter of incoming or load occasions by the presenter protocol.
Knowledge switch between modules
Think about a listing, you choose an merchandise and go to a brand new controller scene. It’s a must to go not less than a novel identifier between VIPER modules to make this attainable.
It is often carried out considerably like this:
- The view calls the didSelect methodology on the presenter with the id
- The presenter forwards the id to the router utilizing the routeFor(id) methodology
- 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 hundreds the info and provides it for the presenter
- The brand new module’s presenter offers the info for the view and presents it
- Element display screen seems with correct knowledge.
In case you are presenting a controller modally you too can go the unique router as a delegate, so you’ll shut it correctly if it is wanted. 😎
Reminiscence administration
Lengthy story brief:
- The builder holds no-one.
- 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 reference of the presenter
- The view retains a robust reference of the presenter
- UIKit holds the views.
You need to verify this within the offered instance, no leaks – I hope so – the whole lot will get launched good and easily after you return or dismiss a module. 🤞
Closing conclusion: ought to I be taught VIPER?
Though VIPER is very criticized due to it is complexity, all I can say it is well worth the effort to be taught its ideas correctly. You will 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 parts primarily based on roles
- Consistency – module skeletons, separation of considerations
- Readability – Single obligations (SOLID)
- Testability – separated small courses, TDD, higher code protection
- Interfaces – module independence, nicely outlined scopes
- Bug fixing – simpler to trace points, find bugs and issues
- Supply management – smaller recordsdata, much less conflicts, cleaner code
- Simple – codebase seems to be comparable, sooner 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 unhealthy, as a result of it is complicated, meh!
I made a follow-up article about VIPER greatest practices that I’ve be taught alongside the journey, you will discover the pattern repository on GitHub. I hope that these tutorials will make it easier to to be taught this structure higher, when you’ve got any questions, be happy to contact me. 👨💻
