有需要的同学也可以这样写; 我不太喜欢让子持有父, 所以让子返回信息给父

//控制
public class Context
{
    //由于state是私有的,外部不能访问,所以需要提供以下方法
    private IState state;

    //封装一次方法
    public void Handle(int num)
    {
        IState tempState = this.state.Handle(num);
        if (tempState != null)
            this.ChangeState(tempState);
    }

    //切换状态
    public void ChangeState(IState state)
    {
        this.state = state;
    }
}

//接口
public interface IState
{
    public IState Handle(int num);
}

//实现接口
public class StateA : IState
{
    public IState Handle(int num)
    {
        Debug.Log(this + "  " + num);

        if (num > 10)
            return new StateB();
        else
            return null;
    }
}

//实现接口
public class StateB : IState
{
    public IState Handle(int num)
    {
        Debug.Log(this + "  " + num);

        if (num <= 10)
            return new StateA();
        else
            return null;
    }
}