Library-agnostic Flutter/Dart code review checklist: widget best practices, state management (BLoC, Riverpod, Provider, GetX, MobX, Signals), Dart idioms, performance, accessibility, security, and clean architecture. USE WHEN reviewing or auditing Flutter/Dart code regardless of state or routing library.
Library-agnostic Flutter/Dart code review checklist: widget best practices, state management (BLoC, Riverpod, Provider, GetX, MobX, Signals), Dart idioms, performance, accessibility, security, and clean architecture. USE WHEN reviewing or auditing Flutter/Dart code regardless of state or routing library.
cluster
mobile-flutter
version
1.0.0
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.
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 or a logging package
dart:developer
log()
Generated files (.g.dart, .freezed.dart, .gr.dart) are up-to-date or in .gitignore
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:developerlog() or the project's logging package; print() has no log levels and cannot be filtered
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
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
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
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)
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.)
The table below maps universal principles to their implementation in popular solutions. Use this to adapt review rules to whichever solution the project uses.
