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
```
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

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

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
```

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

dart

// 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.)
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

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

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

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

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.dart
```
(breaks Dart package encapsulation)
Internal package dependencies use workspace resolution, not hardcoded
```
path: ../../
```
relative strings
All sub-packages share or inherit root
```
analysis_options.yaml
```

11. Navigation and Routing

General principles (apply to any routing solution):

One routing approach used consistently — no mixing imperative
```
Navigator.push
```
with a declarative router
Route arguments are typed — no
```
Map<String, dynamic>
```
or
```
Object?
```
casting
Route paths defined as constants, enums, or generated — no magic strings scattered in code
Auth guards/redirects centralized — not duplicated across individual screens
Deep links configured for both Android and iOS
Deep link URLs validated and sanitized before navigation
Navigation state is testable — route changes can be verified in tests
Back behavior is correct on all platforms

12. Error Handling

Framework error handling:

```
FlutterError.onError
```
overridden to capture framework errors (build, layout, paint)
```
PlatformDispatcher.instance.onError
```
set for async errors not caught by Flutter
```
ErrorWidget.builder
```
customized for release mode (user-friendly instead of red screen)
Global error capture wrapper around
```
runApp
```
(e.g.,
```
runZonedGuarded
```
, Sentry/Crashlytics wrapper)

Error reporting:

Error reporting service integrated (Firebase Crashlytics, Sentry, or equivalent)
Non-fatal errors reported with stack traces
State management error observer wired to error reporting (e.g., BlocObserver, ProviderObserver, or equivalent for your solution)
User-identifiable info (user ID) attached to error reports for debugging

Graceful degradation:

API errors result in user-friendly error UI, not crashes
Retry mechanisms for transient network failures
Offline state handled gracefully
Error states in state management carry error info for display
Raw exceptions (network, parsing) are mapped to user-friendly, localized messages before reaching the UI — never show raw exception strings to users

13. Internationalization (l10n)

Setup:

Localization solution configured (Flutter's built-in ARB/l10n, easy_localization, or equivalent)
Supported locales declared in app configuration

Content:

All user-visible strings use the localization system — no hardcoded strings in widgets
Template file includes descriptions/context for translators
ICU message syntax used for plurals, genders, selects
Placeholders defined with types
No missing keys across locales

Code review:

Localization accessor used consistently throughout the project
Date, time, number, and currency formatting is locale-aware
Text directionality (RTL) supported if targeting Arabic, Hebrew, etc.
No string concatenation for localized text — use parameterized messages

14. Dependency Injection

Principles (apply to any DI approach):

Classes depend on abstractions (interfaces), not concrete implementations at layer boundaries
Dependencies provided externally via constructor, DI framework, or provider graph — not created internally
Registration distinguishes lifetime: singleton vs factory vs lazy singleton
Environment-specific bindings (dev/staging/prod) use configuration, not runtime
```
if
```
checks
No circular dependencies in the DI graph
Service locator calls (if used) are not scattered throughout business logic

15. Static Analysis

Configuration:

```
analysis_options.yaml
```
present with strict settings enabled

Strict analyzer settings:

strict-casts: true

strict-inference: true

strict-raw-types: true

A comprehensive lint rule set is included (very_good_analysis, flutter_lints, or custom strict rules)
All sub-packages in monorepos inherit or share the root analysis options

Enforcement:

No unresolved analyzer warnings in committed code
Lint suppressions (
```
// ignore:
```
) are justified with comments explaining why
```
flutter analyze
```
runs in CI and failures block merges

Key rules to verify regardless of lint package:

```
prefer_const_constructors
```
— performance in widget trees
```
avoid_print
```
— use proper logging
```
unawaited_futures
```
— prevent fire-and-forget async bugs
```
prefer_final_locals
```
— immutability at variable level
```
always_declare_return_types
```
— explicit contracts
```
avoid_catches_without_on_clauses
```
— specific error handling
```
always_use_package_imports
```
— consistent import style

State Management Quick Reference

The table below maps universal principles to their implementation in popular solutions. Use this to adapt review rules to whichever solution the project uses.

Principle	BLoC/Cubit	Riverpod	Provider	GetX	MobX	Signals	Built-in
State container	`Bloc` / `Cubit`	`Notifier` / `AsyncNotifier`	`ChangeNotifier`	`GetxController`	`Store`	`signal()`	`StatefulWidget`
UI consumer	`BlocBuilder`	`ConsumerWidget`	`Consumer`	`Obx` / `GetBuilder`	`Observer`	`Watch`	`setState`
Selector	`BlocSelector` / `buildWhen`	`ref.watch(p.select(...))`	`Selector`	N/A	computed	`computed()`	N/A
Side effects	`BlocListener`	`ref.listen`	`Consumer` callback	`ever()` / `once()`	`reaction`	`effect()`	callbacks
Disposal	auto via `BlocProvider`	`.autoDispose`	auto via `Provider`	`onClose()`	`ReactionDisposer`	manual	`dispose()`
Testing	`blocTest()`	`ProviderContainer`	`ChangeNotifier` directly	`Get.put` in test	store directly	signal directly	widget test

flutter-dart-code-review

NPX Install

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