设计模式-状态模式

当一个控制对象状态转换的条件表达式过于复杂时, 将状态的判断逻辑转移到表示不同状态的一系列类中
当代码中包含大量与对象状态有关的条件语句时, 使用状态模式

状态模式

//抽象状态类
abstract class State
{
    public abstract void Handle(Context context);
}
//具体状态类
class ConcreateStateA : State
{
    public override void Handle(Context context)
    {
        context.State = new ConcreateStateB();
    }
}
class ConcreateStateB : State
{
    public override void Handle(Context context)
    {
        context.State = new ConcreateStateA();
    }
}

class Context
{
    private State state;
    public Context(State state)
    {
        this.state = state;
    }
    public State State
    {
        get{ return state;}
        set
        {
            state = value;
            Console.WriteLine("Current state: " + state.GetType().Name);
        }
    }
    public void Request()
    {
        state.Handle(this);
    }
}
//Client
Context c = new Context(new ConcreateStateA());
c.Request();//每次请求实现状态切换
c.Request();
c.Request();
c.Request();

示例

//不同时间点的工作状态示例

//抽象状态
public abstract class State
{
    public abstract void WriteProgram(Work w);
}
//上午工作状态类
public class ShangWuState : State
{
    public override void WriteProgram(Work w)
    {
        if(w.Hour < 12)
            Console.WriteLine("上午工作状态");
        else
        {
            w.SetState(new ZhongWUState())
            w.WriteProgram();
        }
    }
}
public class ZhongWUState : State
{
    public override void WriteProgram(Work w)
    {
        if(w.Hour < 13)
            Console.WriteLine("中午工作状态");
        else
        {
            w.SetState(new XiaWUState())
            w.WriteProgram();
        }
    }
}
public class XiaWUState : State
{
    public override void WriteProgram(Work w)
    {
        if(w.Hour < 17)
            Console.WriteLine("下午工作状态");
        else
        {
            w.SetState(new WanShangState())
            w.WriteProgram();
        }
    }
}
public class WanShangState : State
{
    public override void WriteProgram(Work w)
    {
        if(w.TaskFinished)
        {
            w.SetState(new RestState());
            w.WriteProgram();
        }
        else
        {
            if(w.Hour < 21)
                Console.WriteLine("晚上工作状态");
            else
            {
                w.SetState(new SleepState())
                w.WriteProgram();
            }
        }
    }
}
public class SleepState : State
{
    public override void WriteProgram(Work w)
    {
        Console.WriteLine("睡觉");
    }
}
public class RestState : State
{
    public override void WriteProgram(Work w)
    {
        Console.WriteLine("下班休息");
    }
}

public class Work
{
    private State current;
    public Work()
    {
        current = new ShangWuState();//初始化为上午状态
    }
    private double hour;
    public double Hour
    {
        get { return hour;}
        set { hour = value;}
    }
    private bool finish = false;
    public bool TaskFinish
    {
        get { return finish;}
        set { finish = value;}
    }
    public void SetState(State s)
    {
        current = s;
    }
    public void WriteProgram()
    {
        current.WriteProgram(this);
    }
}
//Client
Work work = new Work();
work.Hour = 9;
work.WriteProgram();
work.Hour = 12;
work.WriteProgram();
work.Hour = 16;
work.WriteProgram();
work.Hour = 20;
work.WriteProgram();