App essentials in SwiftUI

Views, Scenes, and Apps

• Beside Views, from this year SwiftUI can declare Scenes and Apps

• Views are the basic building blocks, rendering everything on screen. Views can be composed with other Views.

• Views form the content of a Scene, making them platform-independent

• Scenes can also be composed with other Scenes (think of tabs on macOS)

• Scenes form the content of an App

Example

@main
struct MyApp: App {
    @StateObject private var store = Store()

    var body: some Scene {
        WindowGroup {
            MyView(store: store)
        }
    }
}

• In thie example we have an App, MyApp, which contains a Scene, WindowGroup, which contains a view MyView.

• Above the struct declaration we have a new Swift 5.3 attribute @main, which declares this struct as the entry point of our programs execution.

• Declaring Apps is very similar to declaring Views: both comform to a protocol (App vs View), and both need to define a body (of type some Scene vs some View).

• Like Views, also Apps can declare data depenencies, and in this example MyApp declares to be owner of the store object by using the StateObject property wrapper,

WindowGroup

• Scene that allows us to define the primary interface of our app.

• WindowGroup is a scene that allows our app to automatically create multiple scenes containing MyView when needed (this works for having multple windows on both iPad and mac).

• Like in UIKit, an app can provide a shared model for each scene to use, but the state of the views in those scenes will be independent.

• WindowGroup also manages tabs for us on macOS.

• @SceneStorage is a new property wrapper that manages scenes restoration.

More New features

• DocumentGroup: New scene that help us with document based apps, more on this in Build Document-Based Apps in SwiftUI session.

• Settings is a macOS-only scene used for declaring apps preferences

• The Commands API (along with the .commands modifier) let us describe commands to be shown in the main menu on macOS and key commands on iOS.