App Clips & Handoff / Continuity

App Clips — how it works

• Target: own bundle id (parent id + suffix, e.g. .Clip), shipped with the full app; share code via packages, strip the rest with your own #if APPCLIP compilation condition.
• Size (uncompressed, thinned): 10 MB (iOS 14–15), 15 MB (iOS 16+), 100 MB (iOS 17+, digital invocations only — no physical codes, NFC, QR). Third-party SDKs eat it.
• Experiences (App Store Connect): default (one card) + advanced per URL prefix / location. Domain proof: appclips: associated domain + AASA. Launch: webpageURL of a NSUserActivityTypeBrowsingWeb activity = your routing key.
• Limits: no background execution, restricted frameworks (e.g. HealthKit), no cross-app tracking. Ephemeral notifications: NSAppClipRequestEphemeralUserNotification → up to 8 hours without a prompt. NSAppClipRequestLocationConfirmation + APActivationPayload.confirmAcquired(in:) verifies the user is really at the code.
• Upgrade: SKOverlay.AppClipConfiguration (.appStoreOverlay in SwiftUI); the full app inherits only the App Group container. Test: _XCAppClipURL scheme variable; on device, Settings › Developer › Local Experiences.

Handoff & Continuity — how it works

• Advertise: activityType listed in NSUserActivityTypes; small plist userInfo (+ requiredUserInfoKeys), title, webpageURL; isEligibleForHandoff (also ForSearch, ForPrediction). Current via becomeCurrent() or a responder’s userActivity; refresh lazily with needsSave + updateUserActivityState(_:).
• Requirements: same Apple ID / iCloud, BLE + Wi-Fi, Handoff on, same Team ID and activity type in both apps. Big data: continuation streams (supportsContinuationStreams) or the cloud.
• Continue per scene: cold start → connectionOptions.userActivities; running → scene(_:continue:).
• Web↔native: app → Safari via webpageURL; Safari → app needs the activitycontinuation: associated domain (Universal Links use applinks:).
• Universal Clipboard: UIPasteboard items reach nearby devices; keep secrets local with setItems(_:options: [.localOnly: true, .expirationDate: …]). Continuity Camera: iPhone as Mac camera/scanner — nothing to build on iOS.

ArticleView(a)
  .userActivity("com.acme.article") { act in   // advertise
    act.userInfo = ["id": a.id]                  // what, not data
    act.webpageURL = a.webURL                    // Safari fallback
    act.isEligibleForHandoff = true }
  .onContinueUserActivity("com.acme.article") { act in
    if let id = act.userInfo?["id"] as? String { path.append(id) } }
// clip AND full app: the same entry point
.onContinueUserActivity(NSUserActivityTypeBrowsingWeb) { act in
  if let url = act.webpageURL { route(url) } }

Four ways back into a screen

Interview traps

• Quoting “10 MB” without the OS version, or meaning the download size.
• Full app does not handle the clip’s URLs — once installed, every code opens the full app.
• Clip and app share data freely — no: only an App Group; and the clip may vanish.
• Handoff activity never appears: type missing from NSUserActivityTypes, different Team ID, not current, non-plist userInfo, BLE off / other iCloud account.
• Megabytes in userInfo; or expecting Handoff to carry your app’s login — it resumes context, not auth.
• Reading the pasteboard on launch — iOS 16 asks “Allow Paste”; use UIPasteControl / detectPatterns.

Remember

“Clip: a URL, one task, a slot in the App Group. Handoff: my activity, my other device, same iCloud.”

Likely questions

1. How does a clip know what was scanned? — webpageURL of a browsing-web NSUserActivity.
2. Keep a clip’s cart after install? — write it to the shared App Group container.
3. Handoff vs Universal Link? — own activity to own device vs a URL for anyone.
4. Notify from a clip? — ephemeral permission, 8 hours per launch.