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State Machine

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A simple, but generic state machine framework for Dart.

This library is open source, stable and well tested. Development happens on GitHub. Feel free to report issues or create a pull-request there. General questions are best asked on StackOverflow.

Up-to-date class documentation is created with every release.

This code was inspired by work of Vassily Boykov on his Smalltalk Announcement framework.



Follow the Installing instructions on https://pub.dartlang.org/packages/statemachine.

Import the package into your Dart code using:

import 'package:statemachine/statemachine.dart';

Creating a machine

To create a new state machine instantiate Machine:

var machine = new Machine();

Defining states

To create states call Machine.newState and store them in variables. The first state created it the start state of the machine. Optionally you can provide a name as argument to ease debugging.

var startState = machine.newState();
var activeState = machine.newState('active');

It is possible to explicitly create start and stop states of the machine using Machine.newStartState and Machine.newStopState.

Callbacks on states

States support callbacks whenever a state is entered or left.

activeState.onEntry(() => print('activated'));
activeState.onExit(() => print('deactivate'));

Starting and stopping a machine

To start a state machine and set its state to its starting state call Machine.start:


Similarly you can stop a machine by calling Machine.stop.

Transitioning between states

There are various ways in which your machine can switch states.

Manually triggered transition

From anywhere within your code you can enter a specific state by calling State.enter.


Event triggered transition

You can define transitions between states that are triggered by events of any kind using State.onStream. The example below registers for click events when the inactive state is entered. In case of a click event the callback is executed and the state machine transitions into the active state:

startState.onStream(element.onClick, (value) => activeState.enter());

Future completion transition

Also, transitions can be triggered by the completion of a future using State.onFuture. Since futures cannot be suspended or cancelled, the future continues to run even if the owning state is deactivated. Should the state be activated and the future value is already present, then the value is immediately supplied into the callback. Further activations have no effect.

startState.onFuture(computation, (value) => activeState.enter());

Time based transition

Also, you can automatically trigger callbacks after a timeout using State.onTimeout. The following snippet calls the callback 1 second after the active state is entered and falls back to the inactive state:

activeState.onTimeout(const Duration({seconds: 1}), () => startState.enter());

Callbacks often contain code to check for additional constraints and update other objects or UI element before entering a different state. See the tooltip example directory for a more complete illustration of the functionality provided by this library.

Nested machines

Machines can be nested. Simply add another machine that gets started when the state is entered, and stopped when the state is left.




The MIT License, see LICENSE.