更新:
再次感谢你的例子，它们对我很有帮助，我并不是说
夺走他们的一切。
Aren't the currently given examples, as far as I understand them & state-machines, only half of what we usually understand by a state-machine?
In the sense that the examples do change state but that's only represented by changing the value of a variable (and allowing different value- changes in different states), while usually, a state machine should also change its behavior, and behavior not (only) in the sense of allowing different value changes for a variable depending on the state, but in the sense of allowing different methods to be executed for different states.
还是我对状态机及其常用用法有误解?
最初的问题:
我发现了关于c#中的状态机和迭代器块的讨论，以及用于创建状态机和c#的工具，所以我发现了很多抽象的东西，但作为一个新手，所有这些都有点令人困惑。
因此，如果有人能提供一个c#源代码-示例，实现一个简单的状态机，可能只有3,4个状态，那就太好了，只是为了了解它的要点。
这里有些无耻的自我宣传，但在不久前，我创建了一个名为YieldMachine的库，它允许以非常干净和简单的方式描述一个有限复杂性的状态机。例如，考虑一盏灯:
注意，这个状态机有2个触发器和3个状态。在YieldMachine代码中，我们为所有与状态相关的行为编写了一个方法，在这个方法中，我们对每个状态都使用goto，这是一种可怕的暴行。触发器变成Action类型的属性或字段，用一个称为trigger的属性进行修饰。我在下面注释了第一个状态及其转换的代码;接下来的状态遵循相同的模式。
public class Lamp : StateMachine
{
// Triggers (or events, or actions, whatever) that our
// state machine understands.
[Trigger]
public readonly Action PressSwitch;
[Trigger]
public readonly Action GotError;
// Actual state machine logic
protected override IEnumerable WalkStates()
{
off:
Console.WriteLine("off.");
yield return null;
if (Trigger == PressSwitch) goto on;
InvalidTrigger();
on:
Console.WriteLine("*shiiine!*");
yield return null;
if (Trigger == GotError) goto error;
if (Trigger == PressSwitch) goto off;
InvalidTrigger();
error:
Console.WriteLine("-err-");
yield return null;
if (Trigger == PressSwitch) goto off;
InvalidTrigger();
}
}
又短又好，嗯!
这个状态机通过发送触发器来控制:
var sm = new Lamp();
sm.PressSwitch(); //go on
sm.PressSwitch(); //go off
sm.PressSwitch(); //go on
sm.GotError(); //get error
sm.PressSwitch(); //go off
为了澄清，我在第一个状态中添加了一些注释，以帮助您理解如何使用它。
protected override IEnumerable WalkStates()
{
off: // Each goto label is a state
Console.WriteLine("off."); // State entry actions
yield return null; // This means "Wait until a
// trigger is called"
// Ah, we got triggered!
// perform state exit actions
// (none, in this case)
if (Trigger == PressSwitch) goto on; // Transitions go here:
// depending on the trigger
// that was called, go to
// the right state
InvalidTrigger(); // Throw exception on
// invalid trigger
...
这是因为c#编译器实际上在内部为每个使用yield return的方法创建了一个状态机。这个构造通常用于惰性地创建数据序列，但在这种情况下，我们实际上对返回的序列并不感兴趣(反正都是null)，而是对在底层创建的状态行为感兴趣。
StateMachine基类对构造进行一些反射，将代码分配给每个[Trigger]操作，该操作设置Trigger成员并向前移动状态机。
但是你不需要真正理解它的内部原理就能使用它。
您可以编写一个迭代器块，使您能够以编排的方式执行代码块。代码块是如何分解的并不一定要对应于任何东西，这只是你想要如何编码它。例如:
IEnumerable<int> CountToTen()
{
System.Console.WriteLine("1");
yield return 0;
System.Console.WriteLine("2");
System.Console.WriteLine("3");
System.Console.WriteLine("4");
yield return 0;
System.Console.WriteLine("5");
System.Console.WriteLine("6");
System.Console.WriteLine("7");
yield return 0;
System.Console.WriteLine("8");
yield return 0;
System.Console.WriteLine("9");
System.Console.WriteLine("10");
}
在本例中，当调用CountToTen时，还没有实际执行任何东西。您得到的实际上是一个状态机生成器，您可以为它创建一个状态机的新实例。可以通过调用GetEnumerator()来实现。生成的IEnumerator实际上是一个状态机，您可以通过调用MoveNext(…)来驱动它。
因此，在本例中，第一次调用MoveNext(…)时，您将看到“1”写入控制台，下一次调用MoveNext(…)时，您将看到2、3、4，然后是5、6、7、8，然后是9、10。正如您所看到的，这是一种编排事情应该如何发生的有用机制。
让我们从这个简单的状态图开始:
我们有:
4种状态(非活动、活动、暂停和退出)
5种状态转换(开始命令，结束命令，暂停命令，恢复命令，退出命令)。
您可以通过几种方式将其转换为c#，例如在当前状态和命令上执行switch语句，或者在转换表中查找转换。对于这个简单的状态机，我更喜欢一个转换表，它很容易使用Dictionary表示:
using System;
using System.Collections.Generic;
namespace Juliet
{
public enum ProcessState
{
Inactive,
Active,
Paused,
Terminated
}
public enum Command
{
Begin,
End,
Pause,
Resume,
Exit
}
public class Process
{
class StateTransition
{
readonly ProcessState CurrentState;
readonly Command Command;
public StateTransition(ProcessState currentState, Command command)
{
CurrentState = currentState;
Command = command;
}
public override int GetHashCode()
{
return 17 + 31 * CurrentState.GetHashCode() + 31 * Command.GetHashCode();
}
public override bool Equals(object obj)
{
StateTransition other = obj as StateTransition;
return other != null && this.CurrentState == other.CurrentState && this.Command == other.Command;
}
}
Dictionary<StateTransition, ProcessState> transitions;
public ProcessState CurrentState { get; private set; }
public Process()
{
CurrentState = ProcessState.Inactive;
transitions = new Dictionary<StateTransition, ProcessState>
{
{ new StateTransition(ProcessState.Inactive, Command.Exit), ProcessState.Terminated },
{ new StateTransition(ProcessState.Inactive, Command.Begin), ProcessState.Active },
{ new StateTransition(ProcessState.Active, Command.End), ProcessState.Inactive },
{ new StateTransition(ProcessState.Active, Command.Pause), ProcessState.Paused },
{ new StateTransition(ProcessState.Paused, Command.End), ProcessState.Inactive },
{ new StateTransition(ProcessState.Paused, Command.Resume), ProcessState.Active }
};
}
public ProcessState GetNext(Command command)
{
StateTransition transition = new StateTransition(CurrentState, command);
ProcessState nextState;
if (!transitions.TryGetValue(transition, out nextState))
throw new Exception("Invalid transition: " + CurrentState + " -> " + command);
return nextState;
}
public ProcessState MoveNext(Command command)
{
CurrentState = GetNext(command);
return CurrentState;
}
}
public class Program
{
static void Main(string[] args)
{
Process p = new Process();
Console.WriteLine("Current State = " + p.CurrentState);
Console.WriteLine("Command.Begin: Current State = " + p.MoveNext(Command.Begin));
Console.WriteLine("Command.Pause: Current State = " + p.MoveNext(Command.Pause));
Console.WriteLine("Command.End: Current State = " + p.MoveNext(Command.End));
Console.WriteLine("Command.Exit: Current State = " + p.MoveNext(Command.Exit));
Console.ReadLine();
}
}
}
根据个人喜好，我喜欢用GetNext函数来确定地返回下一个状态，用MoveNext函数来改变状态机。
其他替代在此回购https://github.com/lingkodsoft/StateBliss
使用流畅的语法，支持触发器。
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
}
}
您可能希望使用现有的开源有限状态机之一。例如，在http://code.google.com/p/bbvcommon/wiki/StateMachine找到的bbv.Common.StateMachine。它具有非常直观流畅的语法和许多特性，如进入/退出操作、转换操作、保护、分层、被动实现(在调用者的线程上执行)和主动实现(fsm运行在自己的线程上，事件被添加到队列中)。
以Juliets为例，状态机的定义非常简单:
var fsm = new PassiveStateMachine<ProcessState, Command>();
fsm.In(ProcessState.Inactive)
.On(Command.Exit).Goto(ProcessState.Terminated).Execute(SomeTransitionAction)
.On(Command.Begin).Goto(ProcessState.Active);
fsm.In(ProcessState.Active)
.ExecuteOnEntry(SomeEntryAction)
.ExecuteOnExit(SomeExitAction)
.On(Command.End).Goto(ProcessState.Inactive)
.On(Command.Pause).Goto(ProcessState.Paused);
fsm.In(ProcessState.Paused)
.On(Command.End).Goto(ProcessState.Inactive).OnlyIf(SomeGuard)
.On(Command.Resume).Goto(ProcessState.Active);
fsm.Initialize(ProcessState.Inactive);
fsm.Start();
fsm.Fire(Command.Begin);
更新:项目位置已移动到:https://github.com/appccelerate/statemachine
