FSM2 provides an implementation of the core design aspects of the UML2 state diagrams.

FMS2 supports:

• Nested States
• Concurrent Regions
• Guard Conditions
• sideEffects
• onEnter/onExit
• streams
• static analysis tools
• visualisation tools.

Overview

FSM2 uses a builder to delcare each state machine.

Your application may declare as many statemachines as necessary.

Example

import 'package:fsm2/fsm2.dart';

void main() {
  final machine = StateMachine.create((g) => g
    ..initialState(Solid())
    ..state<Solid>((b) => b
      ..on<OnMelted, Liquid>(sideEffect: (e) async => print("I'm melting"))
    ..state<Liquid>((b) {})
 ));

The above examples creates a Finite State Machine (machine) which declares its initial state as being Solid and then declares a single transition which occurs when the event OnMelted event is triggered causing a transition to a new state Liquid.

To trigger an event:

machine.applyEvent(OnMelted());

Documentation

Full documentation is available on gitbooks at:

https://fsm2.onepub.dev/

Example 2

A simple example showing the life cycle of H2O.

import 'package:fsm2/fsm2.dart';

void main() {
  final machine = StateMachine.create((g) => g
    ..initialState(Solid())
    ..state<Solid>((b) => b
      ..on<OnMelted, Liquid>(sideEffect: (e) => print('Melted'),
          )))
    ..state<Liquid>((b) => b
      ..onEnter((s, e) => print('Entering ${s.runtimeType} State'))
      ..onExit((s, e) => print('Exiting ${s.runtimeType} State'))
      ..on<OnFroze, Solid>(sideEffect: (e) => print('Frozen')))
      ..on<OnVaporized, Gas>(sideEffect: (e) => print('Vaporized'))))
    ..state<Gas>((b) => b
      ..on<OnCondensed, Liquid>(sideEffect: (e) => print('Condensed'))))
    ..onTransition((t) => print(
        'Received Event ${t.event.runtimeType} in State ${t.fromState.runtimeType} transitioning to State ${t.toState.runtimeType}')));

  await machine.complete;

  ///   machine.isInState<Hard>()

  print(machine.isInSt<Solid>); // TRUE

  machine.transition(OnMelted());
  print(machine.isInState<Liquid>); // TRUE

  machine.transition(OnFroze());
  print(machine.isInState<Solid>); // TRUE
}

Credits:

FMS2 is derived from the FSM library which in turn was inspired by Tinder StateMachine library.