4.8 State（状态）

【返回目录】

现在，拥有私家车的朋友越来越多，就算你还没有属于自己的座驾，但至少你也一定见过不少汽车了。

所谓没有规矩不成方圆，开车也有开车的规矩，比如开车前要注意检查车门是否都已经关好，如果没关好，交警叔叔见到了可不答应，就算没有被交警看到，为了你和你的亲友的安全，也不应该大而化之嘛。

我们就用计算机程序设计的思想来描述一下这种场景，假设我们有Car这个类，并且我们还创建了AbstractState这样一个抽象类，继承自它的有OpenState和CloseState（而不是仅仅在Car中设置一个bool属性值），这样做的好处就是为了易于维护和扩展。AbstractState具有Drive的方法，而Drive在不同的状态下有不同的反映，Car则通过它当前状态的Drive方法来驾驶车辆，而不是把Drive的各种逻辑也封装在Car中。

   1: using System;

   2:  

   3: namespace Autumoon.DesignPatterns.State

   4: {

   5:     public enum DoorStateSetting

   6:     {

   7:         Closed = 0,

   8:         Opened

   9:     };

  10:  

  11:     public abstract class AbstractState

  12:     {

  13:         public string StateName { get; set; }

  14:  

  15:         abstract public void Drive();

  16:     }

  17:  

  18:     public class OpenedState : AbstractState

  19:     {

  20:         public OpenedState()

  21:         {

  22:             this.StateName = "Opened";

  23:         }

  24:  

  25:         override public void Drive()

  26:         {

  27:             Console.WriteLine("Error: The car cannot be drived as its door(s) is open.");

  28:         }

  29:     }

  30:  

  31:     public class ClosedState : AbstractState

  32:     {

  33:         public ClosedState()

  34:         {

  35:             this.StateName = "Closed";

  36:         }

  37:  

  38:         override public void Drive()

  39:         {

  40:             Console.WriteLine("The car is running.");

  41:         }

  42:     }

  43:  

  44:     public class Car

  45:     {

  46:         public AbstractState CurrentState { get; set; }

  47:  

  48:         public Car()

  49:         {

  50:             this.CurrentState = new ClosedState();

  51:         }

  52:  

  53:         public void SetState(DoorStateSetting newState)

  54:         {

  55:             this.CurrentState = ((newState == DoorStateSetting.Closed)

  56:                 ? new ClosedState() as AbstractState

  57:                 : new OpenedState() as AbstractState);

  58:         }

  59:  

  60:         public void Drive()

  61:         {

  62:             this.CurrentState.Drive();

  63:         }

  64:     }

  65: }

那么我们就来体验一下驾驶的乐趣吧，注意安全哦！

   1: static void Main(string[] args)

   2: {

   3:     #region State

   4:     Car contextColaBottle = new Car();

   5:     Console.WriteLine("Doors' initial state is closed.");

   6:  

   7:     Console.WriteLine("Now drive.");

   8:     contextColaBottle.Drive();

   9:  

  10:     Console.WriteLine("Open the door.");

  11:     contextColaBottle.SetState(DoorStateSetting.Opened);

  12:  

  13:     Console.WriteLine("Now Drive.");

  14:     contextColaBottle.Drive();

  15:     #endregion

  16:  

  17:     Console.ReadLine();

  18: }