Since the Hacker News API returns data in JSON format, our Item struct must conform to the Decodable protocol and provide some coding keys to map the JSON fields to our properties. So, creating a corresponding Swift type is straightforward: struct Item: Identifiable JSON decoding goes inside the model layer The Hacker News API uses a single item entity to represent all its data. In short, they should not know anything about the other layers of the MVVM pattern. They should not know anything about data storage, networking, or how data is presented to the user. Model types only contain data and the code that manipulates it. These are the easiest to implement and the foundation for the whole app’s architecture. You can find the complete Xcode project on GitHub.Īs it’s often the case, we will start creating the model layer of our app. We will use its simple web API to fetch the top 10 news stories from the best stories page. Creating model types to represent the data of an appĪs an example, we will build a small app for Hacker News, a news website for developers like Reddit, known for its (debatable) quality. They contain the domain business logic and the code for data transformation. These foundations are the model types, which represent an app’s data. We can have both controllers (global) and view models (local) in a full app.Īny iOS app needs solid foundations or the whole castle crumbles. So, again the difference between MVC and MVVM disappears. That’s why SwiftUI offers three property wrappers instead of just one. If you make an iOS app with more than one screen, you soon conclude that both local and global states are needed. Since they were required by the framework, it was impossible to get rid of them. These sat squarely between views and controllers/view models. In UIKit, both interpretations were possible because there was a fourth, not-so-hidden layer: view controllers. Objects, then, move from global to local. In MVVM, instead, each view gets its separate view model. It was not uncommon to use singletons for that, although dependency injection became, with time, the preferred alternative. In MVC, the emphasis has always been on making controllers globally shared objects. There is another fundamental difference between MVC and MVVM. MVC: local view models and of global controllers Views connect to observed objects through the and property wrappers.Such an object must expose any property that affects the user interface using the property wrapper.An object must conform to the ObservableObject protocol.While SwiftUI offer several data flow mechanisms, there is only “one” way to connect objects and views: So, in SwiftUI, the most significant difference between MVVM and MVC has disappeared. But you don’t need to learn Combine to make SwiftUI apps. SwiftUI instead uses, behind the scenes, Combine, Apple’s native reactive framework. In UIKit, developers used an FRP framework like RxSwift. This synchronizes the data between the two layers, removing boilerplate code. The most crucial difference with MVC is that MVVM connects the view and the view model layers using a binder. For that reason, I usually talk about architecture in terms of MVC, although I use ideas from both patterns. Looking at the MVC pattern diagram, it does not take a genius to see that MVVM is, practically speaking, the same pattern. MVVM uses binders to connect views and view models That changed with the introduction of SwiftUI. Traditionally, Apple has followed the MVC pattern for both macOS and iOS apps. It found its way into iOS apps only years after the release of the first iPhone. In fact, it was invented by Microsoft architects (of all people). A view model contains the current state of a view, links to other parts of an app’s architecture (e.g., data storage or the network), and handles the user’s interaction. Finally, a view model connects a view to the app’s model.In iOS, it contains the SwiftUI views for your app, which display information and allow user interaction. The view layer is what the user sees on the screen.In the model layer, we find the Swift types representing your app’s data and its domain business logic. ![]() MVVM consists of three layers, from which it takes its name.Įach layer has a well-defined role in the app’s structure, helping you respect the separation of concerns design principle. Like MVC, the Model-View-ViewModel pattern, or MVVM in short, is an architectural pattern that guides how you structure the code in your iOS apps. If I had to define MVVM quickly, I would say that it’s a variation of the MVC pattern. The structure of the MVVM pattern and the roles of its layers While it’s a derivation of MVC, it sports some unique ideas that fit well with how SwiftUI apps work. MVVM is an architectural pattern that helps you structure your iOS apps.
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