Flutter Dart Code Review

Flutter/Dart Code Review Best Practices

Comprehensive, library-agnostic checklist for reviewing Flutter/Dart applications. These principles apply regardless of which state management solution, routing library, or DI framework is used.

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1. General Project Health

• [ ] Project follows consistent folder structure (feature-first or layer-first)
• [ ] Proper separation of concerns: UI, business logic, data layers
• [ ] No business logic in widgets; widgets are purely presentational
• [ ] pubspec.yaml is clean — no unused dependencies, versions pinned appropriately
• [ ] analysis_options.yaml includes a strict lint set with strict analyzer settings enabled
• [ ] No print() statements in production code — use dart:developer log() or a logging package
• [ ] Generated files (.g.dart, .freezed.dart, .gr.dart) are up-to-date or in .gitignore
• [ ] Platform-specific code isolated behind abstractions

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2. Dart Language Pitfalls

• [ ] Implicit dynamic: Missing type annotations leading to dynamic — enable strict-casts, strict-inference, strict-raw-types
• [ ] Null safety misuse: Excessive ! (bang operator) instead of proper null checks or Dart 3 pattern matching (if (value case var v?))
• [ ] Type promotion failures: Using this.field where local variable promotion would work
• [ ] Catching too broadly: catch (e) without on clause; always specify exception types
• [ ] Catching Error: Error subtypes indicate bugs and should not be caught
• [ ] Unused async: Functions marked async that never await — unnecessary overhead
• [ ] late overuse: late used where nullable or constructor initialization would be safer; defers errors to runtime
• [ ] String concatenation in loops: Use StringBuffer instead of + for iterative string building
• [ ] Mutable state in const contexts: Fields in const constructor classes should not be mutable
• [ ] Ignoring Future return values: Use await or explicitly call unawaited() to signal intent
• [ ] var where final works: Prefer final for locals and const for compile-time constants
• [ ] Relative imports: Use package: imports for consistency
• [ ] Mutable collections exposed: Public APIs should return unmodifiable views, not raw List/Map
• [ ] Missing Dart 3 pattern matching: Prefer switch expressions and if-case over verbose is checks and manual casting
• [ ] Throwaway classes for multiple returns: Use Dart 3 records (String, int) instead of single-use DTOs
• [ ] print() in production code: Use dart:developer log() or the project's logging package; print() has no log levels and cannot be filtered

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3. Widget Best Practices

Widget decomposition:

• [ ] No single widget with a build() method exceeding ~80-100 lines
• [ ] Widgets split by encapsulation AND by how they change (rebuild boundaries)
• [ ] Private _build*() helper methods that return widgets are extracted to separate widget classes (enables element reuse, const propagation, and framework optimizations)
• [ ] Stateless widgets preferred over Stateful where no mutable local state is needed
• [ ] Extracted widgets are in separate files when reusable

Const usage:

• [ ] const constructors used wherever possible — prevents unnecessary rebuilds
• [ ] const literals for collections that don't change (const [], const {})
• [ ] Constructor is declared const when all fields are final

Key usage:

• [ ] ValueKey used in lists/grids to preserve state across reorders
• [ ] GlobalKey used sparingly — only when accessing state across the tree is truly needed
• [ ] UniqueKey avoided in build() — it forces rebuild every frame
• [ ] ObjectKey used when identity is based on a data object rather than a single value

Theming & design system:

• [ ] Colors come from Theme.of(context).colorScheme — no hardcoded Colors.red or hex values
• [ ] Text styles come from Theme.of(context).textTheme — no inline TextStyle with raw font sizes
• [ ] Dark mode compatibility verified — no assumptions about light background
• [ ] Spacing and sizing use consistent design tokens or constants, not magic numbers

Build method complexity:

• [ ] No network calls, file I/O, or heavy computation in build()
• [ ] No Future.then() or async work in build()
• [ ] No subscription creation (.listen()) in build()
• [ ] setState() localized to smallest possible subtree

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4. State Management (Library-Agnostic)

These principles apply to all Flutter state management solutions (BLoC, Riverpod, Provider, GetX, MobX, Signals, ValueNotifier, etc.).

Architecture:

• [ ] Business logic lives outside the widget layer — in a state management component (BLoC, Notifier, Controller, Store, ViewModel, etc.)
• [ ] State managers receive dependencies via injection, not by constructing them internally
• [ ] A service or repository layer abstracts data sources — widgets and state managers should not call APIs or databases directly
• [ ] State managers have a single responsibility — no "god" managers handling unrelated concerns
• [ ] Cross-component dependencies follow the solution's conventions:
• In Riverpod: providers depending on providers via ref.watch is expected — flag only circular or overly tangled chains
• In BLoC: blocs should not directly depend on other blocs — prefer shared repositories or presentation-layer coordination
• In other solutions: follow the documented conventions for inter-component communication

Immutability & value equality (for immutable-state solutions: BLoC, Riverpod, Redux):

• [ ] State objects are immutable — new instances created via copyWith() or constructors, never mutated in-place
• [ ] State classes implement == and hashCode properly (all fields included in comparison)
• [ ] Mechanism is consistent across the project — manual override, Equatable, freezed, Dart records, or other
• [ ] Collections inside state objects are not exposed as raw mutable List/Map

Reactivity discipline (for reactive-mutation solutions: MobX, GetX, Signals):

• [ ] State is only mutated through the solution's reactive API (@action in MobX, .value on signals, .obs in GetX) — direct field mutation bypasses change tracking
• [ ] Derived values use the solution's computed mechanism rather than being stored redundantly
• [ ] Reactions and disposers are properly cleaned up (ReactionDisposer in MobX, effect cleanup in Signals)

State shape design:

• [ ] Mutually exclusive states use sealed types, union variants, or the solution's built-in async state type (e.g. Riverpod's AsyncValue) — not boolean flags (isLoading, isError, hasData)
• [ ] Every async operation models loading, success, and error as distinct states
• [ ] All state variants are handled exhaustively in UI — no silently ignored cases
• [ ] Error states carry error information for display; loading states don't carry stale data
• [ ] Nullable data is not used as a loading indicator — states are explicit

// BAD — boolean flag soup allows impossible states
class UserState {
  bool isLoading = false;
  bool hasError = false; // isLoading && hasError is representable!
  User? user;
}

// GOOD (immutable approach) — sealed types make impossible states unrepresentable
sealed class UserState {}
class UserInitial extends UserState {}
class UserLoading extends UserState {}
class UserLoaded extends UserState {
  final User user;
  const UserLoaded(this.user);
}
class UserError extends UserState {
  final String message;
  const UserError(this.message);
}

// GOOD (reactive approach) — observable enum + data, mutations via reactivity API
// enum UserStatus { initial, loading, loaded, error }
// Use your solution's observable/signal to wrap status and data separately

Rebuild optimization:

• [ ] State consumer widgets (Builder, Consumer, Observer, Obx, Watch, etc.) scoped as narrow as possible
• [ ] Selectors used to rebuild only when specific fields change — not on every state emission
• [ ] const widgets used to stop rebuild propagation through the tree
• [ ] Computed/derived state is calculated reactively, not stored redundantly

Subscriptions & disposal:

• [ ] All manual subscriptions (.listen()) are cancelled in dispose() / close()
• [ ] Stream controllers are closed when no longer needed
• [ ] Timers are cancelled in disposal lifecycle
• [ ] Framework-managed lifecycle is preferred over manual subscription (declarative builders over .listen())
• [ ] mounted check before setState in async callbacks
• [ ] BuildContext not used after await without checking context.mounted (Flutter 3.7+) — stale context causes crashes
• [ ] No navigation, dialogs, or scaffold messages after async gaps without verifying the widget is still mounted
• [ ] BuildContext never stored in singletons, state managers, or static fields

Local vs global state:

• [ ] Ephemeral UI state (checkbox, slider, animation) uses local state (setState, ValueNotifier)
• [ ] Shared state is lifted only as high as needed — not over-globalized
• [ ] Feature-scoped state is properly disposed when the feature is no longer active

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5. Performance

Unnecessary rebuilds:

• [ ] setState() not called at root widget level — localize state changes
• [ ] const widgets used to stop rebuild propagation
• [ ] RepaintBoundary used around complex subtrees that repaint independently
• [ ] AnimatedBuilder child parameter used for subtrees independent of animation

Expensive operations in build():

• [ ] No sorting, filtering, or mapping large collections in build() — compute in state management layer
• [ ] No regex compilation in build()
• [ ] MediaQuery.of(context) usage is specific (e.g., MediaQuery.sizeOf(context))

Image optimization:

• [ ] Network images use caching (any caching solution appropriate for the project)
• [ ] Appropriate image resolution for target device (no loading 4K images for thumbnails)
• [ ] Image.asset with cacheWidth/cacheHeight to decode at display size
• [ ] Placeholder and error widgets provided for network images

Lazy loading:

• [ ] ListView.builder / GridView.builder used instead of ListView(children: [...]) for large or dynamic lists (concrete constructors are fine for small, static lists)
• [ ] Pagination implemented for large data sets
• [ ] Deferred loading (deferred as) used for heavy libraries in web builds

Other:

• [ ] Opacity widget avoided in animations — use AnimatedOpacity or FadeTransition
• [ ] Clipping avoided in animations — pre-clip images
• [ ] operator == not overridden on widgets — use const constructors instead
• [ ] Intrinsic dimension widgets (IntrinsicHeight, IntrinsicWidth) used sparingly (extra layout pass)

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6. Testing

Test types and expectations:

• [ ] Unit tests: Cover all business logic (state managers, repositories, utility functions)
• [ ] Widget tests: Cover individual widget behavior, interactions, and visual output
• [ ] Integration tests: Cover critical user flows end-to-end
• [ ] Golden tests: Pixel-perfect comparisons for design-critical UI components

Coverage targets:

• [ ] Aim for 80%+ line coverage on business logic
• [ ] All state transitions have corresponding tests (loading → success, loading → error, retry, etc.)
• [ ] Edge cases tested: empty states, error states, loading states, boundary values

Test isolation:

• [ ] External dependencies (API clients, databases, services) are mocked or faked
• [ ] Each test file tests exactly one class/unit
• [ ] Tests verify behavior, not implementation details
• [ ] Stubs define only the behavior needed for each test (minimal stubbing)
• [ ] No shared mutable state between test cases

Widget test quality:

• [ ] pumpWidget and pump used correctly for async operations
• [ ] find.byType, find.text, find.byKey used appropriately
• [ ] No flaky tests depending on timing — use pumpAndSettle or explicit pump(Duration)
• [ ] Tests run in CI and failures block merges

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7. Accessibility

Semantic widgets:

• [ ] Semantics widget used to provide screen reader labels where automatic labels are insufficient
• [ ] ExcludeSemantics used for purely decorative elements
• [ ] MergeSemantics used to combine related widgets into a single accessible element
• [ ] Images have semanticLabel property set

Screen reader support:

• [ ] All interactive elements are focusable and have meaningful descriptions
• [ ] Focus order is logical (follows visual reading order)

Visual accessibility:

• [ ] Contrast ratio >= 4.5:1 for text against background
• [ ] Tappable targets are at least 48x48 pixels
• [ ] Color is not the sole indicator of state (use icons/text alongside)
• [ ] Text scales with system font size settings

Interaction accessibility:

• [ ] No no-op onPressed callbacks — every button does something or is disabled
• [ ] Error fields suggest corrections
• [ ] Context does not change unexpectedly while user is inputting data

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8. Platform-Specific Concerns

iOS/Android differences:

• [ ] Platform-adaptive widgets used where appropriate
• [ ] Back navigation handled correctly (Android back button, iOS swipe-to-go-back)
• [ ] Status bar and safe area handled via SafeArea widget
• [ ] Platform-specific permissions declared in AndroidManifest.xml and Info.plist

Responsive design:

• [ ] LayoutBuilder or MediaQuery used for responsive layouts
• [ ] Breakpoints defined consistently (phone, tablet, desktop)
• [ ] Text doesn't overflow on small screens — use Flexible, Expanded, FittedBox
• [ ] Landscape orientation tested or explicitly locked
• [ ] Web-specific: mouse/keyboard interactions supported, hover states present

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9. Security

Secure storage:

• [ ] Sensitive data (tokens, credentials) stored using platform-secure storage (Keychain on iOS, EncryptedSharedPreferences on Android)
• [ ] Never store secrets in plaintext storage
• [ ] Biometric authentication gating considered for sensitive operations

API key handling:

• [ ] API keys NOT hardcoded in Dart source — use --dart-define, .env files excluded from VCS, or compile-time configuration
• [ ] Secrets not committed to git — check .gitignore
• [ ] Backend proxy used for truly secret keys (client should never hold server secrets)

Input validation:

• [ ] All user input validated before sending to API
• [ ] Form validation uses proper validation patterns
• [ ] No raw SQL or string interpolation of user input
• [ ] Deep link URLs validated and sanitized before navigation

Network security:

• [ ] HTTPS enforced for all API calls
• [ ] Certificate pinning considered for high-security apps
• [ ] Authentication tokens refreshed and expired properly
• [ ] No sensitive data logged or printed

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10. Package/Dependency Review

Evaluating pub.dev packages:

• [ ] Check pub points score (aim for 130+/160)
• [ ] Check likes and popularity as community signals
• [ ] Verify the publisher is verified on pub.dev
• [ ] Check last publish date — stale packages (>1 year) are a risk
• [ ] Review open issues and response time from maintainers
• [ ] Check license compatibility with your project
• [ ] Verify platform support covers your targets

Version constraints:

• [ ] Use caret syntax (^1.2.3) for dependencies — allows compatible updates
• [ ] Pin exact versions only when absolutely necessary
• [ ] Run flutter pub outdated regularly to track stale dependencies
• [ ] No dependency overrides in production pubspec.yaml — only for temporary fixes with a comment/issue link
• [ ] Minimize transitive dependency count — each dependency is an attack surface

Monorepo-specific (melos/workspace):

• [ ] Internal packages import only from public API — no `package:other/src/internal.

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Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: affaan-m
• Source: affaan-m/ECC
• License: MIT
• Homepage: https://ecc.tools

Install and usage instructions live in the source repository linked above.