Scene

Overview 概要

You create an App by combining one or more instances that conform to the Scene protocol in the app’s body. You can use the built-in scenes that SwiftUI provides, like WindowGroup, along with custom scenes that you compose from other scenes. To create a custom scene, declare a type that conforms to the Scene protocol. Implement the required body computed property and provide the content for your custom scene:

struct MyScene: Scene {
    var body: some Scene {
        WindowGroup {
            MyRootView()
        }
    }
}

A scene acts as a container for a view hierarchy that you want to display to the user. The system decides when and how to present the view hierarchy in the user interface in a way that’s platform-appropriate and dependent on the current state of the app. For example, for the window group shown above, the system lets the user create or remove windows that contain MyRootView on platforms like macOS and iPadOS. On other platforms, the same view hierarchy might consume the entire display when active.

Read the scenePhase environment value from within a scene or one of its views to check whether a scene is active or in some other state. You can create a property that contains the scene phase, which is one of the values in the ScenePhase enumeration, using the Environment attribute:

struct MyScene: Scene {
    @Environment(\.scenePhase) private var scenePhase


    // ...
}

The Scene protocol provides scene modifiers, defined as protocol methods with default implementations, that you use to configure a scene. For example, you can use the onChange(of:perform:) modifier to trigger an action when a value changes. The following code empties a cache when all of the scenes in the window group have moved to the background:

struct MyScene: Scene {
    @Environment(\.scenePhase) private var scenePhase
    @StateObject private var cache = DataCache()


    var body: some Scene {
        WindowGroup {
            MyRootView()
        }
        .onChange(of: scenePhase) { newScenePhase in
            if newScenePhase == .background {
                cache.empty()
            }
        }
    }
}