转换到目标状态并触发转换和状态之间的状态机？

Question

我最近使用了Stateless 状态机。我可以像这样定义转换等的规则：

stateMachine.Configure(State.Unknown)
    .Permit(Trigger.StartApplication, State.Initialized)
    .OnEntry(this.DoBeforeTransition)
    .OnExit(this.DoAfterTransition);

stateMachine.Configure(State.Initialized)
    .Permit(Trigger.CheckSomething, State.SomethingChecked)
    .OnEntry(this.DoBeforeTransition)
    .OnExit(this.DoAfterTransition);

然后您就可以触发触发器来更改状态。但是，如果您想进入特定状态，您需要知道当前状态以及下一个状态。因此，如果没有定义直接转换，状态机的“客户端”需要知道如何达到某个状态。是否有可能调用诸如“goto”之类的东西并且机器自己触发所有必需的触发器？

Answer 1

您可以这样做，因为每个州只有一个“许可证”。如果您有多个“许可”，那么您将无法在工作流程中自动移动（必须有某些原因导致您选择一个许可/触发器而不是另一个）。当我说你“不能”时，这不是技术上的，而是实际上的。

下面是一个在工作流程中自动移动的示例。

using Stateless;
using System;
using System.Runtime.CompilerServices;

namespace MyExample.BAL.WorkFlows
{
    public class TelephoneCallWorkFlow
    {

        private static volatile StateMachine<TelephoneCallStateEnum, TelephoneCallTriggerEnum> SingletonInstance;

        public StateMachine<TelephoneCallStateEnum, TelephoneCallTriggerEnum> Instance
        {
            [MethodImpl(MethodImplOptions.Synchronized)]
            get
            {
                if (SingletonInstance == null)
                {
                    SingletonInstance = new StateMachine<TelephoneCallStateEnum, TelephoneCallTriggerEnum>(TelephoneCallStateEnum.OffHook);

                    SingletonInstance.Configure(TelephoneCallStateEnum.OffHook)
                        .Permit(TelephoneCallTriggerEnum.CallDialed, TelephoneCallStateEnum.Ringing);

                    SingletonInstance.Configure(TelephoneCallStateEnum.Ringing)
                        //removing so there is only one valid path workflow//.Permit(TelephoneCallTriggerEnum.HungUp, TelephoneCallStateEnum.OffHook)
                        .Permit(TelephoneCallTriggerEnum.CallConnected, TelephoneCallStateEnum.Connected);

                    SingletonInstance.Configure(TelephoneCallStateEnum.Connected)
                        //.OnEntry(t => StartCallTimer())
                        //.OnExit(t => StopCallTimer())
                        //removing so there is only one valid path workflow//.Permit(TelephoneCallTriggerEnum.LeftMessage, TelephoneCallStateEnum.OffHook)
                        //removing so there is only one valid path workflow//.Permit(TelephoneCallTriggerEnum.HungUp, TelephoneCallStateEnum.OffHook)
                        .Permit(TelephoneCallTriggerEnum.PlacedOnHold, TelephoneCallStateEnum.OnHold)
                        ;

                    SingletonInstance.Configure(TelephoneCallStateEnum.OnHold)
                        //removing so there is only one valid path workflow//.SubstateOf(TelephoneCallStateEnum.Connected)
                        //removing so there is only one valid path workflow//.Permit(TelephoneCallTriggerEnum.TakenOffHold, TelephoneCallStateEnum.Connected)
                        //removing so there is only one valid path workflow//.Permit(TelephoneCallTriggerEnum.HungUp, TelephoneCallStateEnum.OffHook)
                        .Permit(TelephoneCallTriggerEnum.PhoneHurledAgainstWall, TelephoneCallStateEnum.PhoneDestroyed)
                        ;
                }

                return SingletonInstance;
            }
        }

        public void Fire(TelephoneCallTriggerEnum trigger)
        {
            Console.WriteLine("............[Firing:] {0}", trigger);
            this.Instance.Fire(trigger);
        }
    }
}

public enum TelephoneCallStateEnum
{
    OffHook,
    Ringing,
    Connected,
    OnHold,
    PhoneDestroyed
}

public enum TelephoneCallTriggerEnum
{
    CallDialed,
    HungUp,
    CallConnected,
    LeftMessage,
    PlacedOnHold,
    TakenOffHold,
    PhoneHurledAgainstWall
}

现在是“自动移动”技巧。

            TelephoneCallWorkFlow tcwf1 = new TelephoneCallWorkFlow();
            IEnumerable<TelephoneCallTriggerEnum> myPermittedTriggers = tcwf1.Instance.PermittedTriggers;
            while (null != myPermittedTriggers && myPermittedTriggers.Count() > 0)
            {
                if (myPermittedTriggers.Count() > 1)
                {
                    throw new ArgumentOutOfRangeException("You cannot auto-move the workflow when there's more than one trigger");
                }
                TelephoneCallTriggerEnum nextTrigger = myPermittedTriggers.FirstOrDefault();
                Console.WriteLine("About to call the 'next' trigger: --> {0}", nextTrigger);
                tcwf1.Fire(nextTrigger);
                Console.WriteLine("CurrentState: --> {0}", tcwf1.Instance.State);
                myPermittedTriggers = tcwf1.Instance.PermittedTriggers;
            }

您基本上获得了 PermittedTriggers，并获得了第一个（为了使自动移动工作，每个状态应该只有一个 Permitted-Trigger）......然后调用该触发器。

同样，实际上（不是技术上）您只有在每个州有一个许可/触发器时才会这样做。因此，如果有超过 1 个，为什么我有一个例外。如果有超过 1 个，你可以“获得第一个”，这没有任何意义。