Wes Matlock

VisionOS Scene Phases: Building Apps That Respect the System

Ever been mid-development on a VisionOS app, only to watch it crash when transitioning between phases? Annoying, right? VisionOS apps…

VisionOS Scene Phases: Building Apps That Respect the SystemVisionOS

Ever been mid-development on a VisionOS app, only to watch it crash when transitioning between phases? Annoying, right? VisionOS apps demand finesse — your spatial scenes need to be beautiful, functional, and efficient, all while playing nice with the system’s resource limits. If your app hogs memory or ignores lifecycle cues, it’s game over.

Scene phases are your guiding light. They dictate how and when your app interacts with VisionOS. Let’s break it down and explore how to handle these transitions with precision and care.

Scene Phases 101: What Are They?

VisionOS defines three main scene phases:

  • Active: The app is front and center, running at full steam.
  • Inactive: The app is visible but not interactive (think of it as idling at a red light).
  • Background: The app is out of sight and should behave like a well-mannered house guest — quiet and resource-conscious.

Why Scene Phases Matter

Here’s a question: What happens if your app doesn’t pause animations when transitioning to the background? Not only does it waste system resources, but VisionOS might terminate your app for being greedy. Scene phases give you a clear framework to manage these transitions responsibly.

How to Monitor Scene Phases

You can track scene phases in SwiftUI using the @Environment(.scenePhase) property. Whenever a phase changes, your app can respond appropriately.

Let’s start with a basic implementation

@main  
struct VisionOSApp: App {  
  @Environment(\.scenePhase) private var scenePhase  
  
  var body: some Scene {  
    WindowGroup {  
      ContentView()  
        .onChange(of: scenePhase) { newPhase in  
          print("App phase changed to: \(newPhase)")  
          handlePhaseChange(newPhase)  
        }  
    }  
  }  
  
  private func handlePhaseChange(_ phase: ScenePhase) {  
    switch phase {  
    case .active:  
      print("App is now active. Time to shine!")  
    case .inactive:  
      print("App is inactive. Pause any non-essential tasks.")  
    case .background:  
      print("App is backgrounded. Save resources and state.")  
    default:  
      print("Unknown phase. Double-check your logic.")  
    }  
  }  
}

This snippet ensures your app knows what’s happening at all times. But tracking phases is just the beginning.

Startup and Teardown: Smooth Transitions

Imagine you’re launching a spatial scene with heavy assets — a 3D model of a spaceship, textures, animations, you name it. If your app stutters or takes too long, users will feel the frustration immediately.

Startup Tips

  1. Load Just-in-Time: Don’t load everything at startup. Focus on the essentials first.
  2. Background Threads: Use DispatchQueue.global() to load heavy resources without blocking the UI.
  3. Feedback: A simple ProgressView can save you from users thinking your app is frozen.

Teardown Tips

  1. Release Resources: Unload assets you no longer need.
  2. Persist State: Save the scene’s current status so users can return seamlessly.

Code Example: Managing Startup and Teardown

struct SpatialSceneView: View {  
  @State private var isLoading = true  
  @State private var spatialScene: SpatialScene?  
  
  var body: some View {  
    ZStack {  
      if isLoading {  
        ProgressView("Loading the scene...")  
      } else {  
        RealityView(scene: spatialScene)  
      }  
    }  
    .onAppear { loadScene() }  
    .onDisappear { unloadScene() }  
  }  
  
  private func loadScene() {  
    DispatchQueue.global().async {  
      let loadedScene = SpatialScene(named: "MainScene")  
      DispatchQueue.main.async {  
        spatialScene = loadedScene  
        isLoading = false  
      }  
    }  
  }  
  
  private func unloadScene() {  
    spatialScene = nil // Release memory  
  }  
}

Handling Background Transitions

When your app moves to the background, it’s time to hit the brakes. But what exactly should you stop? Here’s a checklist:

  • Pause Animations: Animations are expensive. Suspend them until the app returns to the foreground.
  • Save State: Users expect to pick up right where they left off.
  • Release Memory: Free up resources tied to inactive or hidden elements.

Code Example: Background Management

@main  
struct VisionOSApp: App {  
  @Environment(\.scenePhase) private var scenePhase  
  @State private var spatialScene: SpatialScene?  
  
  var body: some Scene {  
    WindowGroup {  
      ContentView()  
        .onChange(of: scenePhase) { phase in  
          handlePhaseChange(phase)  
        }  
    }  
  }  
  
  private func handlePhaseChange(_ phase: ScenePhase) {  
    switch phase {  
    case .active: spatialScene?.resume()  
    case .inactive: spatialScene?.pause()  
    case .background: saveSceneState()  
    default: break  
    }  
  }  
  
  private func saveSceneState() {  
    spatialScene?.saveState()  
    print("Scene state saved.")  
  }  
}

Memory Management: Keep It Lean

Spatial apps are memory hogs by nature, but that doesn’t mean you should let them eat everything. Here are three ways to stay lean:

  1. Asset Caching: Reuse assets as much as possible.
  2. Deferred Loading: Only load assets when you need them.
  3. Release Resources: Clean up memory for assets you’re no longer using.

Code Example: Asset Management with Actor

import RealityKit  
  
actor SceneAssetManager {  
  private var assetCache: [String: ModelEntity] = [:]  
  
  func loadAsset(named name: String) async -> ModelEntity {  
    if let cached = assetCache[name] {  
      return cached  
    }  
  
    // Load the asset asynchronously  
    let asset = await ModelEntity.load(named: name)  
    assetCache[name] = asset  
    return asset  
  }  
  
  func clearUnusedAssets() {  
    assetCache.removeAll()  
  }  
}

Using the Actor in Your App

struct SpatialSceneView: View {  
  @State private var spatialScene: SpatialScene?  
  @State private var assetManager = SceneAssetManager()  
  
  var body: some View {  
    RealityView {  
      Task {  
        let model = await assetManager.loadAsset(named: "Spaceship")  
        spatialScene = SpatialScene(entity: model)  
      }  
    }  
    .onDisappear {  
      Task {  
        await assetManager.clearUnusedAssets()  
      }  
    }  
  }  
}

Why Scene Phases Are Key

Handling scene phases isn’t just about following the rules. It’s about creating an experience that feels smooth, responsive, and — dare I say — effortless for your users. Get them right, and your app will be a pleasure to use. Get them wrong, and — well, we’ve all seen the spinning wheel of death.

Got questions? Ideas? Or just want to share your own best practices? Let’s keep the conversation going. The VisionOS developer community is better when we all share what works.

If you want to learn more about native mobile development, you can check out the other articles I have written here: https://medium.com/@wesleymatlock

🚀 Happy coding! 🚀

By Wesley Matlock on December 23, 2024.

Canonical link

Exported from Medium on May 10, 2025.

Written on December 23, 2024