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C#设计模式--状态模式（State Pattern）

news 2025/8/3 21:42:43

状态模式是一种行为设计模式，它允许对象在其内部状态发生变化时改变其行为。这种模式的核心思想是将状态封装在独立的对象中，而不是将状态逻辑散布在整个程序中。

用途

简化复杂的条件逻辑：通过将不同的状态封装在不同的类中，可以避免大量的条件语句，使代码更清晰、更易于维护。
提高可扩展性：添加新的状态或修改现有状态的行为时，只需修改或新增相应的状态类，而不需要修改现有的代码。
提高代码的复用性：状态对象可以在多个上下文对象之间共享，提高代码的复用性。
示例代码及类图

示例1：交通信号灯

public interface ILightState
{void Handle(TrafficLight context);
}public class RedLightState : ILightState
{public void Handle(TrafficLight context){Console.WriteLine("Red Light");context.SetState(new GreenLightState());}
}public class GreenLightState : ILightState
{public void Handle(TrafficLight context){Console.WriteLine("Green Light");context.SetState(new YellowLightState());}
}public class YellowLightState : ILightState
{public void Handle(TrafficLight context){Console.WriteLine("Yellow Light");context.SetState(new RedLightState());}
}public class TrafficLight
{private ILightState _state;public TrafficLight(ILightState initialState){_state = initialState;}public void ChangeLight(){_state.Handle(this);}public void SetState(ILightState state){_state = state;}
}

类图

示例2：订单状态管理

public interface IOrderState
{void Handle(Order context);
}public class PendingState : IOrderState
{public void Handle(Order context){Console.WriteLine("Order is pending");context.SetState(new ProcessingState());}
}public class ProcessingState : IOrderState
{public void Handle(Order context){Console.WriteLine("Order is being processed");context.SetState(new ShippedState());}
}public class ShippedState : IOrderState
{public void Handle(Order context){Console.WriteLine("Order has been shipped");context.SetState(new DeliveredState());}
}public class DeliveredState : IOrderState
{public void Handle(Order context){Console.WriteLine("Order has been delivered");}
}public class Order
{private IOrderState _state;public Order(IOrderState initialState){_state = initialState;}public void Process(){_state.Handle(this);}public void SetState(IOrderState state){_state = state;}
}

类图

示例3：游戏角色状态

public interface ICharacterState
{void Handle(Character context);
}public class IdleState : ICharacterState
{public void Handle(Character context){Console.WriteLine("Character is idle");context.SetState(new WalkingState());}
}public class WalkingState : ICharacterState
{public void Handle(Character context){Console.WriteLine("Character is walking");context.SetState(new RunningState());}
}public class RunningState : ICharacterState
{public void Handle(Character context){Console.WriteLine("Character is running");context.SetState(new IdleState());}
}public class Character
{private ICharacterState _state;public Character(ICharacterState initialState){_state = initialState;}public void Move(){_state.Handle(this);}public void SetState(ICharacterState state){_state = state;}
}

类图

代码解析

状态接口 (IState)：定义了一个 Handle 方法，所有具体状态类都需要实现这个方法。
具体状态 (StateA 和 StateB)：实现了 IState 接口，具体实现了 Handle 方法。在处理完当前状态后，可以改变上下文的当前状态。
上下文类 (Context)：维护一个对当前状态的引用，并提供一个方法 Request 来调用当前状态的 Handle 方法。上下文还提供了一个属性 State 来改变当前状态，并在状态改变时输出相关信息。