Flutter app broken in production.Fixed this session.

Flutter iOS crashes after an SDK upgrade are caused by: a native plugin not yet compatible with the new Flutter version, a Swift or Objective-C interop change in the platform channel interface, a Podfile.lock pinning a CocoaPods dependency version that conflicts with the upgraded plugin requirements, or a breaking change in the iOS runner Xcode project template that requires regeneration with flutter create --platforms=ios. The engineer runs flutter doctor -v to check for environment mismatches, inspects the iOS crash log in Xcode Organizer or via symbolicatecrash, identifies the exact failing method in the native call stack, and either upgrades the offending plugin to a compatible version or applies a targeted iOS platform workaround. The fix is verified on both a simulator and a real device.

UnsatisfiedLinkError on Android in a Flutter app means a native shared library (.so file) expected by a plugin is not present in the APK or AAB for the target ABI. Root causes: the plugin uses a native library that was not included in the abiFilters in the build.gradle, a 64-bit only build excluding armeabi-v7a for devices running older Android that need it, a ProGuard or R8 rule stripping a JNI class that the native library depends on, or the Flutter engine version mismatch between the compiled plugin and the app. The engineer inspects the APK contents using apkanalyzer, checks abiFilters in app/build.gradle, and either adds the missing ABI or fixes the ProGuard rule to keep the JNI interface class.

Continuous widget rebuilds in Flutter are caused by a setState() call triggering a rebuild of a widget that itself calls setState() via a callback or stream, a StreamBuilder subscribed to a stream that emits on every frame, an AnimationController without a defined duration tick listener attached outside the AnimationWidget lifecycle, or a ChangeNotifier calling notifyListeners() in a getter that is accessed during build. The engineer uses Flutter DevTools Widget Rebuild Tracker to see which widget rebuilds per frame, identifies the rebuild-triggering state change, and applies: const constructors to prevent unnecessary child rebuilds, RepaintBoundary to isolate the rebuilding subtree, or refactors the stream subscription into a StreamBuilder with a distinct() filter to suppress identical values.

Push notifications failing exclusively on iOS while working on Android are caused by: the APNs (Apple Push Notification service) certificate or key not configured in the FCM project settings for the iOS app, the app not having the Push Notifications capability enabled in the Xcode entitlements file, the provisioning profile used for the build not including the APNS entitlement (production profile required for production APNs), a missing requestPermission() call before registering the FCM token on iOS (permission is not auto-granted on iOS as it is on Android), or the FCM token not being obtained on iOS because the user denied notification permission. The engineer checks the APNs key upload in Firebase Console, verifies the entitlements file, and adds the requestPermission() flow with a proper UNNotificationSettings check.

Every QuickHire Flutter engineer passes: a live debugging exercise on a broken Flutter app with a hidden widget rebuild loop and an iOS platform channel crash, a written assessment covering Dart language internals (isolates, async/await, Streams, null safety), Flutter rendering pipeline (RenderObject, Layout vs Paint pass, RepaintBoundary), state management patterns (Riverpod, Bloc, Provider, GetX trade-offs), and native platform integration (method channels, pigeon, FFI), plus a portfolio review of production Flutter apps published on both App Store and Google Play. Only the top 3% pass all stages. PM matches engineers to your Flutter version, state management library, and specific platforms (iOS, Android, Flutter Web, desktop).

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