如何封装.NET无状态状态机

Question

我有一个项目,其中主要是线性工作流程.我正在尝试使用.NET Stateless 库充当工作流引擎/状态机.那里的例子数量有限,但我把以下代码放在一起:

private StateMachine<WorkflowStateType, WorkflowStateTrigger> stateMachine;
private StateMachine<WorkflowStateType, WorkflowStateTrigger>.TriggerWithParameters<Guid, DateTime> registrationTrigger;
private Patient patient;

public Patient RegisterPatient(DateTime dateOfBirth)
{
    configureStateMachine(WorkflowState.Unregistered);
    stateMachine.Fire<DateTime>(registrationTrigger, dateOfBirth);
    logger.Info("State changed to: " + stateMachine.State);
    return patient;
}

private void configureStateMachine(WorkflowState state)
{
    stateMachine = new StateMachine<WorkflowState, WorkflowTrigger>(state);

    registrationTrigger = stateMachine.SetTriggerParameters<DateTime>(WorkflowTrigger.Register);

    stateMachine.Configure(WorkflowState.Unregistered)
        .Permit(WorkflowTrigger.Register, WorkflowStateType.Registered);

    stateMachine.Configure(WorkflowState.Registered)
        .Permit(WorkflowTrigger.ScheduleSampling, WorkflowState.SamplingScheduled)
        .OnEntryFrom(registrationTrigger, (dateOfBirth) => registerPatient(dateOfBirth));
}

private void registerPatient(DateTime dateOfBirth)
{
    //Registration code
}

如您所见,我正在使用Stateless Fire()重载,它允许我传入一个触发器.这样我就可以拥有状态机进程业务逻辑,在这种情况下,代码可以注册一个新患者.

这一切都有效,但现在我想将所有状态机代码移动到另一个类中来封装它,我在这方面遇到了麻烦.我这样做的挑战是:

• 实例化StateMachine对象需要您指定state,并且State是一个只能在实例化时设置的只读属性.
• 我registrationTrigger必须在状态机配置期间实例化,并且必须由调用类提供.

如何克服这些项并封装状态机代码？

Answer 1

Scott Hanselman 撰写了一篇文章,介绍了一个库.另外,他们的GitHub上提供的示例很少,包括Scott的文章中提到的Bug实现示例,它封装了状态机.

下面是如何从行为中提取状态的示例:

public class PatientRegistrationState
{
    private StateMachine<WorkflowState, WorkflowTrigger> stateMachine;
    private StateMachine<WorkflowState, WorkflowStateTrigger>.TriggerWithParameters<DateTime> registrationTrigger;

    public PatientRegistrationState(State initialState = default(State)) {
        stateMachine = new StateMachine<WorkflowState, WorkflowTrigger>(initialState);

        stateMachine.Configure(WorkflowState.Unregistered)
            .Permit(WorkflowTrigger.Register, WorkflowStateType.Registered);

        stateMachine.Configure(WorkflowState.Registered)
            .Permit(WorkflowTrigger.ScheduleSampling, WorkflowState.SamplingScheduled)
            .OnEntryFrom(registrationTrigger, (date) => OnPatientRegistered(date));
    }

    public WorkflowState State => stateMachine.State;
    public Action<DateTime> OnPatientRegistered {get; set;} = (date) => { };

    // For state changes that do not require parameters.
    public void ChangeTo(WorkflowTrigger trigger)
    {
        stateMachine.Fire<DateTime>(trigger);
    }

    // For state changes that require parameters.
    public void ChangeToRegistered(DateTime dateOfBirth)
    {
        stateMachine.Fire<DateTime>(registrationTrigger, dateOfBirth);        
    }

    // Change to other states that require parameters...
}

public class PatientRegistration
{
    private PatientRegistrationState registrationState;
    private Patient patient;

    public PatientRegistration()
    {
        registrationState = PatientRegistrationState(WorkflowState.Unregistered)
        {
            OnPatientRegistered = RegisterPatient;
        }
    }

    public Patient RegisterPatient(DateTime dateOfBirth)
    {
        registrationState.ChangeToRegistered(dateOfBirth);
        logger.Info("State changed to: " + registrationState.State);
        return patient;
    }

    private void RegisterPatient(DateTime dateOfBirth)
    {
        // Registration code
    }
}