Capacitor UIScene Migration (8.4 -> 8.5)

Capacitor 8.5 moved the iOS template to the UIScene lifecycle because Xcode 27 requires it. It shipped as a breaking minor, iOS only. The 8.5 core still runs the AppDelegate path, so bumping the dependency alone does not break an app; the app project must adopt scenes before it can build with Xcode 27 (and before Capacitor 9).

Canonical source: https://capacitorjs.com/docs/updating/8-5

When to Use

TRIGGER when:

• App is on @capacitor/ios 8.0-8.4, or on 8.5 without UIApplicationSceneManifest in Info.plist
• Xcode 27 build or runtime warning "CLIENT OF UIKIT REQUIRES UPDATE: This process does not adopt UIScene lifecycle"
• npx cap migrate printed UIScene migration: project is in a partial state ... Skipping automated migration
• After adding a scene manifest: custom URL scheme, universal link, appUrlOpen, or AppDelegate applicationDidBecomeActive code stopped running
• Build error on tmpWindow or TmpViewController after updating to 8.5
• A plugin author asks whether their iOS code survives the scene lifecycle
• Preparing a Capacitor 8 -> 9 upgrade from 8.4 or earlier

Do not use:

• Capacitor 8 -> 9 package/native upgrade itself -> capacitor-app-upgrade-v8-to-v9 / capacitor-plugin-upgrade-v8-to-v9
• Setting up deep links from scratch -> capacitor-deep-linking
• Android (UIScene is iOS only)
• Multi-window or resizable layout work beyond lifecycle adoption

Live Project Snapshot

!node -e "const fs=require('fs');if(!fs.existsSync('package.json'))process.exit(0);const pkg=JSON.parse(fs.readFileSync('package.json','utf8'));const out=[];for(const s of ['dependencies','devDependencies','peerDependencies']){for(const [n,v] of Object.entries(pkg[s]||{})){if(n.startsWith('@capacitor/'))out.push(s+'.'+n+'='+v)}}const p='ios/App/App/';out.push('SceneDelegate.swift='+fs.existsSync(p+'SceneDelegate.swift'));if(fs.existsSync(p+'Info.plist'))out.push('UIApplicationSceneManifest='+fs.readFileSync(p+'Info.plist','utf8').includes('UIApplicationSceneManifest'));if(fs.existsSync(p+'AppDelegate.swift'))out.push('configurationForConnecting='+fs.readFileSync(p+'AppDelegate.swift','utf8').includes('UISceneConfiguration(name:'));console.log(out.join('\n'))"

Facts the Audit Depends On

• Once UIApplicationSceneManifest exists, iOS stops calling these AppDelegate methods: application(_:open:options:), application(_:continue:restorationHandler:), applicationDidBecomeActive, applicationWillResignActive, applicationDidEnterBackground, applicationWillEnterForeground. Code in them silently stops running. No compiler warning.
• Still called on the AppDelegate: didFinishLaunchingWithOptions, applicationWillTerminate, push token registration (didRegisterForRemoteNotificationsWithDeviceToken / didFailToRegister...) and remote-notification delivery. UIApplication.*Notification lifecycle notifications still fire.
• SceneDelegateProxy (CAPSceneDelegateProxy.swift) re-posts .capacitorOpenURL, .capacitorOpenUniversalLink (same payload) and CDVPluginHandleOpenURL, and mirrors the URL into ApplicationDelegateProxy.shared.lastURL. Cold-start URLs and user activities are held until the first .capacitorViewDidAppear, so plugins see them after registration and App.getLaunchUrl() works.
• New 8.5-only notifications: .capacitorSceneWillConnect, .capacitorSceneOpenURL, .capacitorSceneOpenUniversalLink (object = UIScene, payload in userInfo). Not posted on 8.4.
• JS pause/resume are driven by UIScene.didEnterBackgroundNotification / willEnterForegroundNotification, filtered to the bridge's scene.
• Removed in 8.5: TmpViewController, CapacitorBridge.tmpWindow, tmpViewControllerAppeared. Any reference is a build error; present from bridge.viewController.
• The 8.5 SceneDelegate creates the window and CAPBridgeViewController() in code. A custom bridge subclass set in Main.storyboard must be instantiated in the SceneDelegate instead.
• cap migrate (CLI 8.5+) classifies the project by three signals: manifest in Info.plist, SceneDelegate.swift on disk, UISceneConfiguration(name: in AppDelegate.swift. 0/3 -> migrates; 3/3 -> skips as done; 1-2/3 -> warns "partial state" and does nothing. It never overwrites an existing SceneDelegate.swift. It warns (does not fix) on UIApplication.shared.applicationState, tmpWindow, TmpViewController, and custom open url: / continue userActivity: bodies.

Procedure

Audit, report, ask, then edit. Never edit before the user has seen the findings.

1. Detect repo type. ios/App/App.xcodeproj -> app. Package.swift / *.podspec with CAPPlugin sources and no app project -> plugin; go to step 9.
2. Check versions and package manager. @capacitor/ios must reach ^8.5.0. ios/App/Podfile -> CocoaPods; ios/App/CapApp-SPM -> SPM. The SceneDelegate is identical for both.
3. Classify with the snapshot's three signals (eligible / migrated / partial).
4. Audit with the commands in references/audit-patterns.md, covering ios/App and installed plugins in node_modules. Record file:line for each hit.
5. Report grouped as: build blockers (tmpWindow, TmpViewController), needs a decision (custom URL/activity/lifecycle bodies, existing SceneDelegate, storyboard custom class, third-party SDK forwarding), informational (observers that keep working, applicationState, issues inside node_modules).
6. Ask at the real judgement calls:
   • Custom body in open url: / continue userActivity:: move it into scene(_:openURLContexts:) / scene(_:continue:) next to the proxy call (show the body first).
   • Custom lifecycle code: move to sceneDidBecomeActive / sceneWillResignActive / sceneDidEnterBackground / sceneWillEnterForeground, or to UIApplication notification observers.
   • Remove the now-dead AppDelegate URL methods, or keep them (harmless).
   • SDKs that need URL forwarding (Facebook, Google Sign-In, OAuth redirect libraries): check their docs for a scene-delegate entry point and call it from the SceneDelegate.
7. Apply.
   • Eligible and template-shaped: npm i @capacitor/core@^8.5.0 @capacitor/ios@^8.5.0, npm i -D @capacitor/cli@^8.5.0, then npx cap migrate. Read every log line; anything skipped is handled by hand for that step only. Then apply step 6 decisions.
   • Partial or customized: merge only the missing pieces using references/scene-delegate-template.md. Keep existing keys, methods and custom logic. Register the new file per references/pbxproj-registration.md.
8. Sync and build: npx cap sync ios, then build (see Verification). Re-check the three signals: all must be true.
9. Plugin repos: audit and advise only, using references/plugin-audit.md. Never touch app files from a plugin repo; edit plugin sources only when the user asks.

Verification

npx cap sync ios
xcodebuild -project ios/App/App.xcodeproj -scheme App -configuration Debug \
  -destination 'generic/platform=iOS Simulator' build   # use -workspace App.xcworkspace for CocoaPods
grep -rn --include=*.swift -E '\btmpWindow\b|\bTmpViewController\b' ios/App   # expect nothing

On a device or simulator:

• App launches to the web view (no black screen).
• Background then foreground: JS pause and resume fire once each.
• Custom scheme, warm (app running): appUrlOpen fires. Use xcrun simctl openurl booted myscheme://test.
• Custom scheme, cold (app killed, then link): appUrlOpen fires and App.getLaunchUrl() returns the URL.
• Universal link routes in, if the app has associated domains (needs a real domain and AASA file).
• Push: token still arrives (registration event), and a tapped notification opens the app.
• Any moved custom logic (analytics on foreground, SDK URL handlers) runs.

Error Handling

• cap migrate says "partial state" -> expected for hand-edited projects; merge by hand (step 7). Do not reset files without asking.
• Black screen after migration -> SceneDelegate does not create a window, or the UISceneDelegateClassName in Info.plist does not match the class. Use $(PRODUCT_MODULE_NAME).SceneDelegate and the template window setup.
• Cannot find 'SceneDelegate' in scope in AppDelegate -> file not in the App target; see references/pbxproj-registration.md.
• Value of type 'CapacitorBridge' has no member 'tmpWindow' -> delete the reference; present from bridge?.viewController.
• Deep link works warm but not cold -> URL logic still lives in the AppDelegate, or the app reads it before the bridge appears; rely on appUrlOpen + getLaunchUrl().
• Custom bridge subclass not used (plugins registered in capacitorDidLoad missing) -> instantiate the subclass in scene(_:willConnectTo:).
• pbxproj hand edit makes Xcode refuse to open the project -> revert and add the file through Xcode.

References

Only load a reference when its topic is in play.

Related skills: capacitor-app-upgrade-v8-to-v9, capacitor-plugin-upgrade-v8-to-v9, capacitor-app-upgrades, capacitor-deep-linking, capacitor-push-notifications.