![]() ![]() But here comes the crazy part: Not only will our views have view models – our coordinators will have view models, too!Ī coordinator in SwiftUI consists of two components: We will be using an MVVM approach (quite similar to our MVVM approach in a previous blog post), so each view will have a corresponding view model conforming to ObservableObject, defining the view’s state. ![]() ![]() Now, let’s see how we can translate these responsibilities to SwiftUI! A Coordinator in SwiftUI It creates view controllers and manages the memory exchange between them (e.g.It defines which transitions are performed when certain events occur, such as presenting a new view controller or pushing it onto the current navigation stack.whether it is used inside of a UINavigationController, a UITabBarController or just as is. In UIKit, a coordinator has the following responsibilities: Instead, we need to think about what role our coordinators play in UIKit and how these individual responsibilities can be transferred to SwiftUI. Therefore, we can define a SwiftUI view as a function of the current state, or mathematically put:Īs a result, performing transitions in SwiftUI is not a simple method call as in UIKit, which makes it more of a challenge to adopt the Coordinator pattern. Whenever that state changes, the view is recreated and the user interface is updated accordingly. Rather than describing the process of how to build a user interface with long-living objects, we simply define what the view should look like on the basis of the current state of the app. The reason is that SwiftUI follows a declarative approach. How can we now make this work in SwiftUI? As mentioned in the introduction, we cannot simply use the same kind of structure as in UIKit. In combination with the Coordinator pattern, we can use coordinators to exchange information between different view models and to define transition logic. ViewModels prepare and forward the information retrieved from the Models to View components, which in turn define the user interface. As with other app architectures, Model components are built for persistence, networking, and calculation capabilities of an application. In conjunction with the MVVM (Model-View-ViewModel) architecture pattern, we get a clear separation of concerns between view components and business logic. You can look at them as the “glue” between different scenes (view controllers or “screens”) since their job is to control the data flow between these scenes, define which kind of transition is performed on the basis of a certain event, and create new scenes. The Coordinator pattern, as introduced to the iOS community by Soroush Khanlou in 2015, extracts transition logic between view controllers into separate components which we call coordinators. If you can’t wait to see how it works, here’s the link to our sample app repo upfront: In this article, we’re going to explore how we can implement the Coordinator pattern with declarative UI frameworks such as SwiftUI and then create a little sample app to showcase how the pattern can be applied. That’s due to the fundamentally changed paradigms and the fact that views are no longer class objects, but short-lived instances of structs. It turns out that it’s not as easy as replacing all the UIKit views (and view controllers) with their SwiftUI equivalents. (To further simplify the implementation, we introduced XCoordinator, a framework that provides tools to make coordinators and transitions as elegant and powerful as possible.) However, with SwiftUI released roughly two and a half years ago and maturing ever since, the question arises of how to use the Coordinator pattern with SwiftUI. ![]() Implementing apps with the Coordinator pattern in UIKit is pretty straight-forward once you’ve understood the idea. This increases the reusability of view components (such as view controllers), reduces responsibilities of the frequently overcrowded UIViewController implementations and makes connections, such as transitions and data exchange, between view components more visible. When developing iOS apps with UIKit, many developers have used the Coordinator pattern to abstract away the connections between individual view components. ![]()
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