Flutter BLoC & Clean State Architecture Standard

--- description: Flutter BLoC & Clean State Architecture Standard - Guardrails for Flutter: strict BLoC (Business Logic Component) pattern, immutable state objects via Freezed, separation of UI and business logic, and memory leak prevention. globs: lib/**/*.dart alwaysApply: false verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/flutter-bloc" --- # Flutter BLoC & Clean State Architecture Standard > **Severity**: HIGH | **Category**: mobile > **Anti-Pattern Warning**: AI sprays setState() across deep widget trees, leading to uncontrolled rebuilds and state loss. ## System Constraints You are an enterprise Flutter engineer. Use flutter_bloc for state management. State objects must be immutable (Equatable or Freezed). Never perform network or database calls directly inside Widget build methods. Close StreamControllers and BloCs in dispose(). ## Strict Guidelines - Separate widgets into dumb presentation widgets and smart BlocBuilder / BlocConsumer containers. - State classes must inherit from Equatable or be generated with Freezed to prevent duplicate renders. - Always cancel subscriptions or close BloC instances to prevent memory leaks. ## Bad vs Good Implementations ### BlocConsumer for State Handling and One-off Side Effects #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Mixing async side effects with setState causes UI jank and makes widget logic impossible to unit test. ```dart // Anti-pattern: Business logic and dialogs inside build method class MyPage extends StatefulWidget { @override _MyPageState createState() => _MyPageState(); } class _MyPageState extends State<MyPage> { void _submit() async { setState(() => _loading = true); // Triggers full tree rebuild await apiCall(); } } ``` #### Production Standard (Correct) > **Standard**: BlocConsumer listens for one-off side effects (SnackBars/navigation) and cleanly builds UI for state changes. ```dart // Production Standard: BlocConsumer separating UI and side effects BlocConsumer<AuthBloc, AuthState>( listener: (context, state) { if (state is AuthFailure) { ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text(state.error))); } }, builder: (context, state) { if (state is AuthLoading) return const CircularProgressIndicator(); return ElevatedButton( onPressed: () => context.read<AuthBloc>().add(const AuthLoginRequested()), child: const Text('Log In'), ); }, ) ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Flutter BLoC & Clean State Architecture Standard

Flutter BLoC & Clean State Architecture Standard defines an industrial-grade behavioral standard for mobile engineering. Guardrails for Flutter: strict BLoC (Business Logic Component) pattern, immutable state objects via Freezed, separation of UI and business logic, and memory leak prevention. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: AI sprays setState() across deep widget trees, leading to uncontrolled rebuilds and state loss. Without an explicit system instruction file, developers spend hours debugging silent failures.

Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	AI sprays setState() across deep widget trees, leading to uncontrolled rebuilds and state loss.	High	Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production. Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture Inconsistency	AI assistants produce mixed paradigms across files, creating fragmented codebase conventions.	Medium	Increases cognitive load during code reviews and leads to maintenance debt across engineering teams. Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.

Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

Separate widgets into dumb presentation widgets and smart BlocBuilder / BlocConsumer containers.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

State classes must inherit from Equatable or be generated with Freezed to prevent duplicate renders.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

Always cancel subscriptions or close BloC instances to prevent memory leaks.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

Technical Questions & Answers

Frequently Asked Technical Questions

Common questions developers face when configuring AI coding assistants for this stack:

Q:Why is Flutter BLoC & Clean State Architecture Standard critical for AI coding assistants?

Guardrails for Flutter: strict BLoC (Business Logic Component) pattern, immutable state objects via Freezed, separation of UI and business logic, and memory leak prevention. Without explicit behavioral boundaries, AI coding assistants (Cursor, Claude Code, Windsurf, Codex) rely on training data averages, which frequently produce deprecated, inefficient, or vulnerable code patterns.

Q:How does adopting this rule prevent AI hallucinations?

This rule explicitly declares what the AI must avoid (AI sprays setState() across deep widget trees, leading to uncontrolled rebuilds and state loss.) and prescribes verified positive examples. Grounding the LLM with negative and positive pairs eliminates guesswork.

Q:Which AI coding environments are supported?

This specification is multi-platform compatible: Cursor (.cursor/rules/*.mdc & .cursorrules), Anthropic Claude Code (CLAUDE.md), Windsurf (.windsurfrules), Codex / Cline (AGENTS.md), and GitHub Copilot (.github/copilot-instructions.md).

Q:Can I combine this rule with other technology stacks?

Yes. Use the Interactive Stack Builder or download an Agent Pack to merge this rule with other frontend, backend, database, security, and DevOps rules without syntax collision.