Flutter Debugging

Logging

• Use a centralized AppLogger class for all logging: NEVER use print() or raw debugPrint()
• Define log levels: verbose, debug, info, warning, error, fatal
• In dev flavor: log everything (verbose and above)
• In staging: log info and above
• In production: log warning and above only, route to Crashlytics
• Include context in logs: AppLogger.error('Failed to fetch user', error: e, stackTrace: st)
• NEVER log sensitive data (passwords, tokens, PII) at any level

Flutter DevTools

• Use Widget Inspector to debug layout issues and identify unnecessary rebuilds
• Use Performance Overlay (showPerformanceOverlay: true) to monitor frame rates
• Use Timeline View to identify jank: target 16ms per frame (60fps)
• Use Memory View to detect memory leaks and monitor allocation patterns
• Use Network Profiler to inspect Dio requests/responses during development

Debugging Strategies

• Layout Issues: Use debugPaintSizeEnabled = true to visualize widget boundaries (see flutter-devtools).
• Overflow Errors: Check RenderFlex overflowed: use Expanded, Flexible, or constrain dimensions
• Unbounded Height: Wrap ListView in SizedBox or use shrinkWrap: true with NeverScrollableScrollPhysics
• Rebuild Tracking: Add debugPrint('$runtimeType rebuild') temporarily to identify excessive rebuilds (remove before commit)
• Agentic Hot Reload: In Flutter 3.44+/Dart 3.12+, AI coding agents and MCP servers detect code modifications and trigger hot reload automatically. Keep a debug daemon running (flutter run) to enable real-time updates.
• Async Errors: Always catch and log errors in try-catch blocks with stack traces
• Use assert() for development-time invariant checks that are stripped in release builds

Memory Management

• Dispose ALL controllers, subscriptions, Timer, and AnimationController in dispose()
• Use late initialization in initState(): never inline-initialize disposable objects
• Use WeakReference for caches that should not prevent garbage collection
• Profile memory with DevTools Memory tab: watch for monotonically increasing allocations
• Watch for common leaks: undisposed listeners, closures capturing BuildContext, global streams without cancellation

Performance Profiling

• Always profile with --profile mode (not debug): flutter run --profile --flavor dev
• Use Timeline.startSync / Timeline.finishSync for custom performance tracing of critical paths
• Impeller Graphics: Impeller is the default rendering engine on iOS and Android. Pre-compiling shaders (SkSL warmup) is deprecated and no longer needed. If rendering artifacts occur, verify compilation logs in the terminal.
• Target metrics for displays:
  • 60Hz screens: < 16.6ms frame build time.
  • 90Hz screens: < 11.1ms frame build time.
  • 120Hz screens: < 8.3ms frame build time.
  • Screen transition: < 100ms.
  • Cold start: < 2s.

Error Boundaries

• Route errors to Crashlytics in staging/prod (FlutterError.onError = FirebaseCrashlytics.instance.recordFlutterFatalError)
• Set FlutterError.onError and PlatformDispatcher.instance.onError to catch framework and async errors
• Wrap critical widget subtrees in custom error boundary widgets that show fallback UI instead of red screens
• In release mode: NEVER show stack traces to users: show user-friendly error messages only

Runtime Error Taxonomy

Categorize and fix Dart runtime errors systematically using static analysis and type system knowledge.

Type System Soundness

• Method Overrides: Maintain sound return types (covariant) and parameter types (contravariant). Use covariant keyword when intentionally tightening parameter types.
• Generics: Add explicit type annotations to generic classes (List<int> not List<dynamic>). Never assign List<dynamic> to a typed list.
• Downcasting: Avoid implicit downcasts from dynamic. Use explicit casts (as Type) only when runtime type is guaranteed.
• Enable Strict Casts: Add to analysis_options.yaml:

  analyzer:
    language:
      strict-casts: true
  

Null Safety Error Patterns

Rules:

• Avoid ! operator: prefer pattern matching or early returns.
• Use late only when initialization is guaranteed before first access.
• Use _ wildcard (Dart 3.7+) for unused variables.

Automated Resolution Workflow

# 1. Identify all errors
dart analyze . --fatal-infos

# 2. Preview automated fixes
dart fix --dry-run

# 3. Apply automated fixes
dart fix --apply