# 状态模式

属于行为型模式。
允许对象在内部状态发生改变时改变它的行为，对象看起来好像修改了它的类。
对象的行为依赖于它的状态（属性），并且可以根据它的状态改变而改变它的相关行为。

在面临大量的 if else 语句时，使用状态模式可以消除这些 if else 语句，并且可以封装变化点，新增条件和状态时，只需要在原来的基础上进行扩展即可。

在有限状态机中使用了这种模式。

# 类图

	namespace BehavioralPatterns_StatePattern
	{
	/// <summary>
	/// 状态类
	/// </summary>
	public abstract class State
	{
	/// <summary>
	/// 触发条件
	/// </summary>
	public ITrigger Trigger;

	/// <summary>
	/// 进入状态
	/// </summary>
	public abstract void EnterState();
	}
	}

	namespace BehavioralPatterns_StatePattern
	{
	public class State_1 : State
	{
	public State_1()
	{
	Trigger = new Trigger_1();
	}

	public override void EnterState()
	{
	Console.WriteLine("State_1");
	}
	}
	}

	namespace BehavioralPatterns_StatePattern
	{
	public class State_0 : State
	{
	public State_0()
	{
	Trigger = new Trigger_0();
	}

	public override void EnterState()
	{
	Console.WriteLine("State_0");
	}
	}
	}

	namespace BehavioralPatterns_StatePattern
	{
	/// <summary>
	/// 条件接口
	/// </summary>
	public interface ITrigger
	{
	/// <summary>
	/// 条件触发就切换状态
	/// </summary>
	/// <returns></returns>
	public State HandleTrigger(StateController control);
	}
	}

	namespace BehavioralPatterns_StatePattern
	{
	public class Trigger_0 : ITrigger
	{
	public State HandleTrigger(StateController control)
	{
	if (control.Time >= 10)
	{
	return new State_1();
	}
	return control.CurrentState;
	}
	}
	}

	namespace BehavioralPatterns_StatePattern
	{
	public class Trigger_1 : ITrigger
	{
	public State HandleTrigger(StateController control)
	{
	if (control.Time < 10)
	{
	return new State_0();
	}
	return control.CurrentState;
	}
	}
	}

	namespace BehavioralPatterns_StatePattern
	{
	/// <summary>
	/// 状态控制类
	/// </summary>
	public class StateController
	{
	/// <summary>
	/// 当前的状态
	/// </summary>
	public State CurrentState;
	/// <summary>
	/// 状态的切换条件
	/// </summary>
	public ITrigger CurrentTrigger;

	/// <summary>
	/// 用于切换状态
	/// </summary>
	public float Time;

	public StateController()
	{
	// 设置默认状态
	Time = 0;
	CurrentState = new State_0();
	CurrentTrigger = CurrentState.Trigger;
	}

	/// <summary>
	/// 执行当前状态的操作
	/// </summary>
	public void StateAction()
	{
	CurrentState.EnterState();
	}

	/// <summary>
	/// 用线程检测条件的触发
	/// </summary>
	public void ChangeState()
	{
	while (true)
	{
	CurrentState = CurrentTrigger.HandleTrigger(this);
	CurrentTrigger = CurrentState.Trigger;
	Thread.Sleep(100);
	}
	}
	}
	}

	namespace BehavioralPatterns_StatePattern
	{
	public class Program
	{
	private static void Main()
	{
	StateController stateController = new StateController();

	Thread thread = new Thread(stateController.ChangeState);
	thread.Start();

	stateController.StateAction();

	stateController.Time = 12;
	Thread.Sleep(500);

	stateController.StateAction();

	thread.Abort();
	}
	}
	}

运行结果：
State_0
State_1