flutter-bug-investigation

name	flutter-bug-investigation
description	Use when investigating bugs, crashes, or unexpected behavior in a Flutter app. Especially when issues involve Bloc state not emitting, null safety errors, BuildContext after async, GetIt DI failures, method channel mismatches, widget rebuilds, or memory leaks.

Bug Solving Skill (Flutter)

Foundation: Extends shared-bug-investigation with Flutter patterns.

Flutter Context

flutter --version && grep "sdk:" pubspec.yaml
grep -r "BlocProvider\|ChangeNotifier\|GetX" lib/  # State management

RCA: Check All Layers (data/domain/view)

# View Layer: Bloc/Cubit, widgets, state
find lib/feature/<feature>/view -name "*.dart"

# Domain Layer: Models, repository interfaces, business logic
find lib/feature/<feature>/domain -name "*.dart"

# Data Layer: DTOs, datasources, API calls
find lib/feature/<feature>/data -name "*.dart"

Debug by layer: View (Bloc emits?) → Domain (model mapping?) → Data (DTO parsing?)

Common Bug Patterns

Bloc State

// ❌ Missing emit → ✅ Add emit(LoadingState()), emit(LoadedState(data)), emit(ErrorState())

Null Safety

// ❌ user!.name → ✅ user?.name ?? 'Guest'

BuildContext After Async

// ❌ Navigator.pop(context) after await → ✅ if (!mounted) return; Navigator.pop(context);

GetIt DI

// ❌ Not registered → ✅ Add @injectable, run build_runner

Method Channels

// ❌ Wrong name → ✅ Match iOS/Android channel name

Widget Rebuilds

// ❌ BlocBuilder wraps Scaffold → ✅ Wrap only body

Memory Leaks

// ❌ Stream not closed → ✅ Override close(), call super.close()

Error Quick Reference

Error	Fix
type 'Null' is not a subtype	Add ?? defaults
Looking up deactivated widget	Check mounted
Object not registered	Add @injectable, run build_runner
MissingPluginException	Implement native iOS/Android
setState() after dispose()	Cancel timers/streams
RenderBox overflow	Fix constraints

Tools

flutter analyze              # Must pass (0 errors)
flutter test                 # All tests
flutter run --profile        # Performance

Validation

• flutter analyze = 0 errors
• flutter test passes
• Manual test fixed
• Tested iOS + Android (if platform-specific)