Does C# include finite state machines?

问题

I've recently read about the boost::statechart library (finite state machines) and I loved the concept.

Does C# have a similar mechanism ? Or can it be implemented using a specific design pattern?

回答1:

Yes, C# has iterator blocks which are compiler-generated state machines.

If you wish to implement you own state machine you can create custom implementations of the IEnumerable<T> and IEnumerator<T> interfaces.

Both of these approaches highlight the .NET framework's implementation of the iterator pattern.

回答2:

.NET 4 Update 1 now supports it in the following class: System.Activities.Statements.StateMachine

Here is a tutorial on how to use it. Here's a hands on lab.

回答3:

Workflow Foundation (.NET 3.0) has a state machine workflow. 4.0 doesn't have exactly the same thing currently, but you can definitely create a state machine workflow using 4.0.

回答4:

I maintain an open-source project which implements (among other things) a generic finite state machine for .NET. It is built on top of QuickGraph, so you get many graph-analysis algorithms for free.

See this page for more information about the project, and specifically "Jolt.Automata : Finite State Machines" for more information about the feature.

回答5:

Check out Stateless -> http://code.google.com/p/stateless/. Its a lightweight alternative to the heavier WWF.

Here's a couple of articles by the author of the tool:

State Machines in Domain Models

Parameterised Triggers and Re-entrant States in Stateless

回答6:

The things that come near to FSMs are workflows in .NET 3.5, however, also workflows are not exactly FSMs.

The power of using FSMs is that you can create them explicitly in your code, having less chance of creating bugs. Besides, of course some systems are FSMs by nature, so it is more natural to code them like so.

回答7:

Windows Workflow Foundation (WF) that is part of the base class library in 3.0 and 3.5 includes a state-machine workflow design to manage state machines for your applications.

They have completely rewritten workflow for the upcoming 4.0 release, and the new WF 4.0 classes do not natively support state-machines, but all of the 3.0/3.5 classes are still fully supported under 4.0.

回答8:

Other alternative in this repo https://github.com/lingkodsoft/StateBliss used fluent syntax, supports triggers.

    public class BasicTests
    {
        [Fact]
        public void Tests()
        {
            // Arrange
            StateMachineManager.Register(new [] { typeof(BasicTests).Assembly }); //Register at bootstrap of your application, i.e. Startup
            var currentState = AuthenticationState.Unauthenticated;
            var nextState = AuthenticationState.Authenticated;
            var data = new Dictionary<string, object>();

            // Act
            var changeInfo = StateMachineManager.Trigger(currentState, nextState, data);

            // Assert
            Assert.True(changeInfo.StateChangedSucceeded);
            Assert.Equal("ChangingHandler1", changeInfo.Data["key1"]);
            Assert.Equal("ChangingHandler2", changeInfo.Data["key2"]);
        }

        //this class gets regitered automatically by calling StateMachineManager.Register
        public class AuthenticationStateDefinition : StateDefinition<AuthenticationState>
        {
            public override void Define(IStateFromBuilder<AuthenticationState> builder)
            {
                builder.From(AuthenticationState.Unauthenticated).To(AuthenticationState.Authenticated)
                    .Changing(this, a => a.ChangingHandler1)
                    .Changed(this, a => a.ChangedHandler1);

                builder.OnEntering(AuthenticationState.Authenticated, this, a => a.OnEnteringHandler1);
                builder.OnEntered(AuthenticationState.Authenticated, this, a => a.OnEnteredHandler1);

                builder.OnExiting(AuthenticationState.Unauthenticated, this, a => a.OnExitingHandler1);
                builder.OnExited(AuthenticationState.Authenticated, this, a => a.OnExitedHandler1);

                builder.OnEditing(AuthenticationState.Authenticated, this, a => a.OnEditingHandler1);
                builder.OnEdited(AuthenticationState.Authenticated, this, a => a.OnEditedHandler1);

                builder.ThrowExceptionWhenDiscontinued = true;
            }

            private void ChangingHandler1(StateChangeGuardInfo<AuthenticationState> changeinfo)
            {
                var data = changeinfo.DataAs<Dictionary<string, object>>();
                data["key1"] = "ChangingHandler1";
            }

            private void OnEnteringHandler1(StateChangeGuardInfo<AuthenticationState> changeinfo)
            {
                // changeinfo.Continue = false; //this will prevent changing the state
            }

            private void OnEditedHandler1(StateChangeInfo<AuthenticationState> changeinfo)
            {                
            }

            private void OnExitedHandler1(StateChangeInfo<AuthenticationState> changeinfo)
            {                
            }

            private void OnEnteredHandler1(StateChangeInfo<AuthenticationState> changeinfo)
            {                
            }

            private void OnEditingHandler1(StateChangeGuardInfo<AuthenticationState> changeinfo)
            {
            }

            private void OnExitingHandler1(StateChangeGuardInfo<AuthenticationState> changeinfo)
            {
            }

            private void ChangedHandler1(StateChangeInfo<AuthenticationState> changeinfo)
            {
            }
        }

        public class AnotherAuthenticationStateDefinition : StateDefinition<AuthenticationState>
        {
            public override void Define(IStateFromBuilder<AuthenticationState> builder)
            {
                builder.From(AuthenticationState.Unauthenticated).To(AuthenticationState.Authenticated)
                    .Changing(this, a => a.ChangingHandler2);

            }

            private void ChangingHandler2(StateChangeGuardInfo<AuthenticationState> changeinfo)
            {
                var data = changeinfo.DataAs<Dictionary<string, object>>();
                data["key2"] = "ChangingHandler2";
            }
        }
    }

    public enum AuthenticationState
    {
        Unauthenticated,
        Authenticated
    }
}

来源：https://stackoverflow.com/questions/1406986/does-c-sharp-include-finite-state-machines