游戏中的设计模式九（命令模式）

博客地址：blog.liujunliang.com.cn

概述

在游戏开发中，行为请求者与行为实现者往往是一种紧耦合性

请求一命令的形式包裹在对象中，并传给调用对象。调用对象寻找可以处理该命令的合适对象

并把该命令传给相应的对象，该对象执行命令

写在前面

本文介绍在Unity3d客户端执行按钮点击操作，发起相应的命令并执行命令

将操作行为的请求者与实现者解耦。常常运用于在对行为进行“记录”、“撤销/恢复”、“事务”等处理

模式角色

调用者(Invoker)、命令(Command) 、接收者(Received)

开发案例

调用者类

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Invoker
{
    ICommand jumpCommand = new JumpCommand(new JumpReceived());
    ICommand pickCommand = new PickCommand(new PickReceived());

    public ICommand ExcuteCommand()
    {
        if (Input.GetKeyDown(KeyCode.J))
        {
            return jumpCommand;
        }
        else if (Input.GetKeyDown(KeyCode.P))
        {
            return pickCommand;
        }

        return null;
    }
}

命令类

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public abstract class ICommand 
{
    public IReceived received;
    public abstract void Excute();
}

具体命令类---跳跃类

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class JumpCommand : ICommand
{
    public JumpCommand(IReceived received)
    {
        this.received = received;
    }

    public override void Excute()
    {
        Debug.Log("发出跳跃命令");
        received.Action();
    }
}

具体命令类---拾取类

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PickCommand : ICommand
{

    public PickCommand(IReceived received)
    {
        this.received = received;
    }

    public override void Excute()
    {
        Debug.Log("发出拾取命令");
        received.Action();
    }
}

接受者类

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public abstract class IReceived
{
    public abstract void Action();
}

具体接受者类---跳跃类

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class JumpReceived : IReceived
{
    public override void Action()
    {
        Debug.Log("接收跳跃请求");
    }
}

具体接受者类---拾取类

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PickReceived : IReceived
{
    public override void Action()
    {
        Debug.Log("接收拾取请求");
    }
}

测试类

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class CommandPattern : MonoBehaviour
{
    private GameObject slider { get; set; }
    private Invoker invoker { get; set; }

    private void Start()
    {
        slider = GameObject.Find("Slider");

        invoker = new Invoker();
    }

    private void Update()
    {
        if (slider != null)
        {
            ICommand command = invoker.ExcuteCommand();
            if (command != null)
            {
                command.Excute();
            }
        }
    }
}

测试完成，这样命令模式将键盘操作请求与接收通过命令Command进行隔离

这样我们通过对命令模式进行扩展，可以对各个行为进行记录、事务/撤销(Undo、Redo)、恢复操作

即将各个命令进行添加到容器内，用于存放各个命令

模式分析

优点：降低系统耦合性、新的命令很容易融入到系统内

确定：导致系统中有过多的具体命令类与接收者类

博客地址：blog.liujunliang.com.cn