Stateless状态机的简单应用

一、为什么使用状态机？

        在实际开发中，会经常遇到某个对象的状态需要管理，根据不同操作，来变更到各种相应的值，最基础的做法就是if-else，好处在于简单；坏处在于代码冗长不便于维护，比如参数要精准控制从什么状态变到什么状态的话最坏情况需要写一遍所有状态的if-else，然后每个动作都要判断一轮，枚举数量少于5个时，感觉不出来什么，但更多时就知道写if-else有多恶心了

然后状态机就出场了，其相对if-else的优点在于代码集中管理，每一种状态的变化都能硬性控制可以怎么变化，变化前后可以产生什么操作（反正就是精准控制状态要较if-else好很多）

二、例子

1、引用Nuget包，“管理解决方案的Nuget程序包”直接搜Stateless，安装即可。代码中using Stateless;

2、简单使用

//2.1创建状态机，LeaveStatus和LeaveAction都是枚举，leave（业务对象：请假的表单）是追踪状态的对象，状态的字段名叫Status
var _machine = new StateMachine<LeaveStatus, LeaveAction>(() => leave.Status, s => leave.Status = s);

//2.2配置状态机，以下代码意思是当业务状态处于Draft状态时，可以发生Submit动作，动作之后状态变为UnderApprove
_machine.Configure(LeaveStatus.Draft).Permit(LeaveAction.Submit, LeaveStatus.UnderApprove);

//2.3发生动作，action是枚举值（状态机会根据发生的动作改编成相应的状态，如果是没有定义的动作，会抛异常，这个抛异常可以重写，下面再说）
_machine.Fire(action);

3、本人的一种封装，根据业务需要去自行查阅源码完善吧，代码应该不算难，都能看得懂

    public class Leave
    {
        public long Id { get; set; }
        public LeaveStatus Status { get; set; }
        public DateTime? FirSaveTime { get; set; }
        public DateTime? SubmitTime { get; set; }
        public DateTime? PassTime { get; set; }
        public DateTime? RejectTime { get; set; }
    }

    public enum LeaveStatus
    {
        [Description("拒绝")]
        Rejected = -1,
        [Description("草稿")]
        Draft = 0,
        [Description("审批中")]
        UnderApprove = 1,
        [Description("审批通过")]
        Approved = 2
    }

    public enum LeaveAction
    {
        [Description("拒绝")]
        Reject = -1,
        [Description("保存")]
        Save = 0,
        [Description("提交")]
        Submit = 1,
        [Description("审批通过")]
        Pass = 2,
    }

    public class LeaveManager
    {
        private Leave _leave;
        StateMachine<LeaveStatus, LeaveAction> _machine;
        //StateMachine<LeaveStatus, LeaveAction>.TriggerWithParameters<string> _triggerWithPara;

        public LeaveManager(Leave leave)
        {
            _leave = leave;
            _machine = new StateMachine<LeaveStatus, LeaveAction>(() => leave.Status, s => leave.Status = s);
            _machine.OnUnhandledTrigger((status, action) => throw new FriendlyException($"请假的状态为{status.GetDescription()}，不可以执行{action.GetDescription()}")); //重写抛异常的方法
            Configure();
        }

        public void Execute(LeaveAction action)
        {
            _machine.Fire(action);
        }

        private void Configure()
        {
            _machine.Configure(LeaveStatus.Draft)
                .OnEntry(OnSaveEntry)
                .OnExit(OnSaveExit)
                .PermitReentry(LeaveAction.Save)
                .Permit(LeaveAction.Submit, LeaveStatus.UnderApprove);
            //.Ignore(LeaveAction.Save);
            _machine.Configure(LeaveStatus.UnderApprove)
                .OnEntry(OnSubmitEntry)
                .OnExit(OnSubmitExit)
                .PermitReentry(LeaveAction.Submit)
                .Permit(LeaveAction.Save, LeaveStatus.Draft)
                .Permit(LeaveAction.Pass, LeaveStatus.Approved)
                .Permit(LeaveAction.Reject, LeaveStatus.Rejected);
        }

        private void OnSaveExit(StateMachine<LeaveStatus, LeaveAction>.Transition obj)
        {
            
        }

        private void OnSaveEntry(StateMachine<LeaveStatus, LeaveAction>.Transition obj)
        {
            if (!_leave.FirSaveTime.HasValue)
            {
                _leave.FirSaveTime = DateTime.Now;
            }
        }

        private void OnSubmitExit(StateMachine<LeaveStatus, LeaveAction>.Transition obj)
        {

        }

        private void OnSubmitEntry(StateMachine<LeaveStatus, LeaveAction>.Transition obj)
        {
            if (!_leave.SubmitTime.HasValue)
            {
                _leave.SubmitTime = DateTime.Now;
            }
        }
    }

然后在外面就可以这么调用了

new LeaveManager(leave).Execute(action);

注意，一个状态机对应一个追踪对象也就是业务实体，比如这里的leave，多个业务对象就需要多个状态机

项目源代码 https://github.com/dotnet-state-machine/stateless