JIntent

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Lightweight, explicit Intent + State + Side Effect architecture for Flutter (MVI-inspired)

Table of Contents

  • Overview
  • Why JIntent?
  • Quick Start
  • Core Concepts
  • Architecture
  • Minimal Example
  • Side Effects
  • Concurrency & Ordering
  • Testing
  • Comparison
  • Migration (if any)
  • Roadmap (Short Term)
  • Contributing
  • License

Overview

JIntent provides a simple, explicit way to:

  1. Represent immutable UI state (JState).
  2. Trigger domain actions via Intents (JIntent subclasses).
  3. Update state in a single, predictable point (JController).
  4. Emit one-off side effects (navigation, dialogs, toasts) without polluting state (JEffect / side effect channels).

Goal: Clarity and testability with minimal boilerplate.

Why JIntent?

Problem in typical apps How JIntent helps
Mixed UI + logic Controller centralizes state transitions
Side effects duplicated Dedicated side effect stream/channel
Hard to test flows Intents are discrete, testable units
Race conditions (Document your chosen intent handling policy)
State mutation Immutability via copyWith patterns

Quick Start

Add dependency:

dependencies:
  jintent: ^X.Y.Z

Import:

import 'package:jintent/jintent.dart';

Create State:


@immutable
class CounterState extends JState {
  final int counter;

  const CounterState({required this.counter});

  @override
  CounterState copyWith({int? newStateCounter}) =>
      CounterState(counter: newStateCounter ?? counter);

  @override
  List<Object?> get props => [counter];

  factory CounterState.initialState() => const CounterState(counter: 0);
}

Declare Intents:

class DecrementUseCase extends JSyncUseCase<int, int> {
  @override
  Either<Exception, int> run(int currentValue) {
    final newValue = currentValue - 1;

    if (newValue < -10) {
      return Left(Exception('Value cannot be less than -10'));
    }
    return Right(newValue);
  }
}

Controller:

class CounterController extends JController<CounterState> {
  // With injection dependence
  final _getCurrentCounterValueIntent = Di.sl<GetCurrentCounterValueIntent>();
  final _incrementIntent = Di.sl<IncrementIntent>();
  final _decrementIntent = Di.sl<DecrementIntent>();

  // other common to Creation
  // final _getCurrentCounterValueIntent = GetCurrentCounterValueIntent()
  // final _incrementIntent = IncrementIntent();
  // final _decrementIntent = DecrementIntent();

  CounterController(super.initialState);

  void loadCounter() {
    intent(_getCurrentCounterValueIntent);
  }

  void increment() => intent(_incrementIntent);

  void decrement() => intent(_decrementIntent);

  @override
  void onInit() {}
}

UI:


import 'package:counter/src/presentation/counter/controllers/controller.dart';
import 'package:counter/src/presentation/counter/presentation/counter_effect_handler.dart';
import 'package:counter/src/presentation/counter/states/state.dart';
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:jintent/jintent.dart';

class CounterView extends ConsumerStatefulWidget {
  const CounterView({super.key});

  @override
  ConsumerState<ConsumerStatefulWidget> createState() => _CounterViewState();
}

class _CounterViewState extends ConsumerState<CounterView> {
  final throttler = JThrottler(const Duration(milliseconds: 200));

  late final CounterController _counterController;

  JSideEffectHandler<CounterState> get _sideEffectHandler =>
      CounterEffectHandler(_counterController);

  @override
  void initState() {
    super.initState();

    _counterController = ref.read(couterControllerProvider.notifier);
  }

  @override
  Widget build(BuildContext context) {
    final counter = ref.watch(
      couterControllerProvider.select((value) => value.counter),
    );

    return JEffectListener(
      controller: _counterController,
      handler: _sideEffectHandler,
      child: Scaffold(
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              const Text('You have pushed the button this many times:'),
              Text(
                '$counter',
                style: Theme.of(context).textTheme.headlineMedium,
              ),
            ],
          ),
        ),
        floatingActionButton: Column(
          mainAxisSize: MainAxisSize.max,
          crossAxisAlignment: CrossAxisAlignment.end,
          mainAxisAlignment: MainAxisAlignment.end,
          children: [
            FloatingActionButton.extended(
              label: const Text('Increment'),
              heroTag: 'Increment',
              onPressed: () => throttler.call(_counterController.increment),
              tooltip: 'Increment',
              icon: const Icon(Icons.exposure_plus_1_outlined),
            ),
            const SizedBox(height: 10),
            FloatingActionButton.extended(
              label: const Text('Decrement'),
              heroTag: 'Decrement',
              onPressed: () => throttler.call(_counterController.decrement),
              tooltip: 'Decrement',
              icon: const Icon(Icons.exposure_minus_1_sharp),
            ),
          ],
        ),
      ),
    );
  }
}

Core Concepts

  • JState: Immutable snapshot of UI data.
  • JIntent: User or system intention (e.g., SubmitLogin, LoadItems).
  • JController<S, I>: Receives intents, updates state, emits side effects.
  • Side Effect: One-shot event (navigation, toast, analytics).
  • Effect Channel / Stream: Decoupled delivery of ephemeral events.

Architecture

Flow (simplified): User Action -> Intent -> Controller.handle -> (New State) + (Optional Side Effect)

State updates propagate to UI via a ValueListenable/Stream. Side effects consumed once by a listener (e.g. using a StreamBuilder or dedicated hook).

⚡ Side Effects (Modern Overview)

Side effects (JEffect) model transient events (navigation, dialogs, toasts) outside of state.
Key types:

  • JEffect
  • JFireAndForgetEffect (no return value)
  • JResultEffect

Quick example:

final confirmed = await controller.emitAndWaitSideEffect(
  DeleteDialogEffect(itemName: 'File.txt'),
);
if (confirmed) {
  controller.intent(DeleteItemIntent(...));
}

If an awaited effect has no handler, the default strategy completes it silently (warnAndAutoComplete).
Configure a different strategy with:

JEffectsConfig().unhandledStrategy = UnhandledEffectStrategy.throwError;

Concurrency & Ordering

JIntent processes intents in a predictable, sequential order by default.

  • Queue (FIFO): Intents are enqueued and handled one at a time, ensuring state transitions are applied in the order they were received.
  • No Parallel Mutations: This avoids race conditions and makes state changes easy to reason about.
  • Custom Policies: Advanced users can implement custom intent handling strategies (e.g., debouncing, throttling, dropping, or merging intents) by extending the controller or using middleware.

Best practice:
Document your chosen concurrency policy in your controller, especially if you change the default behavior. This helps maintain clarity and prevents subtle bugs in complex flows.

Testing

Recommended strategy:

  1. Given initial state
  2. When: dispatch intent
  3. Await completion
  4. Assert new state + captured side effects

Comparison (High Level)

Feature JIntent Bloc Redux Plain Riverpod
Side effects channel Yes Yes (via Bloc) Middleware needed Provider-dependent
Boilerplate Low Medium High Low
Immutable state Yes Yes Yes Depends
Intent semantics Explicit classes Events Actions Method calls
Concurrency control (Document) Per event loop Middleware Custom

Migration

If upgrading from 1.x to 2.x:

  • Update import paths.
  • Adjust side effect API rename.
  • See CHANGELOG for removed symbols. (Provide MIGRATION.md if many items.)

Roadmap (Short Term)

  • ✓ Formal concurrency policy documentation
  • ✓ Logging observer utility
  • Advanced examples (debounce, pagination, streaming)
  • DevTool overlay (visualize intents/states)
  • Undo/Redo experiment

Contributing Guidelines

Thank you for your interest in contributing to this project.
This document sets the official policies and guidelines for collaboration.

1. Communication

  • Before starting any development, please open an issue to discuss the proposal.
  • All contributions must align with the project's vision, objectives, and standards.

2. Git Workflow

  • Use branch names with the following format:

    • feature/<short-description>
    • fix/<short-description>
    • chore/<short-description>

  • Example: feature/offline-sync

  • Commit messages must follow the Conventional Commits standard:

    • feat: New feature
    • fix: Bug fix
    • docs: Documentation
    • refactor: Internal refactor, no functional change
    • test: Adding or updating tests

3. Code Quality

  • Every change must include:
    • Unit and/or integration tests.
    • An entry in CHANGELOG.md under [Unreleased].
    • Compliance with the project’s linting and formatting rules.

4. Pull Requests

  • PRs must be clear, concise, and focused only on related changes.
  • The PR description should include:
    • The problem it solves.
    • The changes introduced.
    • Instructions for testing.
  • At least one reviewer must approve the PR, and all automated checks must pass.

5. Versioning and Releases

  • We follow Semantic Versioning (SemVer):
    • MAJOR: Breaking changes.
    • MINOR: Backward-compatible new features.
    • PATCH: Bug fixes.
  • All releases must be documented in CHANGELOG.md.

6. Code of Conduct

All interactions must follow the Code of Conduct, fostering a professional, inclusive, and respectful environment.

License

MIT © 2025 TodoFlutter.com

FAQ

Q: How do I avoid duplicate side effects after Hot Reload?
A: Keep effects listener registration inside initState and cancel in dispose; do not re-emit past effects (channel is one-shot).

Q: Can I dispatch intents from inside another intent?
A: Prefer composing functions or scheduling a new intent after current finishes to maintain linear flow.

Q: Does JIntent support cancellation?
A: (Document if implemented; show API or mark as planned.)

Libraries

jintent