PHP Design Patterns - Command Pattern_PHP Tutorial

PHP Design Pattern - Command Pattern

Command pattern: In software systems, "behavior requester" and "behavior implementer" usually present a "tight coupling". But in some situations, such as "recording, undo/redo, transaction" and other processing of behaviors, this kind of tight coupling that cannot resist changes is inappropriate. In this case, how to decouple the "behavior requester" from the "behavior implementer"? Abstract a set of behaviors into objects to achieve loose coupling between them. This is the command mode.

Class diagram:

Character Analysis:

Abstract command: defines the interface of the command and declares the execution method.

Specific command: The command interface implementation object is a "virtual" implementation; it usually holds the receiver and calls the receiver's function to complete the operation to be performed by the command.

Command receiver: receiver, the object that actually executes the command. Any class may become a receiver as long as it can implement the corresponding functions required by the command.

Controller: requires the command object to execute the request, usually holds the command object, and can hold many command objects. This is where the client actually triggers the command and requires the command to perform the corresponding operation, which is equivalent to the entrance to the command object.

Core code:

<!--?php
/**
 * Created by PhpStorm.
 * User: LYL
 * Date: 2015/6/4
 * Time: 20:21
 */

/**
 * 电视机是请求的接收者，
*遥控器上有一些按钮，不同的按钮对应电视机的不同操作。
*抽象命令角色由一个命令接口来扮演，有三个具体的命令类实现了抽象命令接口，
*这三个具体命令类分别代表三种操作：打开电视机、关闭电视机和切换频道。
*显然，电视机遥控器就是一个典型的命令模式应用实例。
 */

/**命令接收者
 * Class Tv
 */
class Tv
{
    public $curr_channel=0;

    /**
     * 打开电视机
     */
    public function turnOn()
    {
        echo The television is on..<br/-->;
    }

    /**
     * 关闭电视机
     */
    public function turnOff()
    {
        echo The television is off..
;
    }

    /**切换频道
     * @param $channel    频道
     */
    public function turnChannel($channel)
    {
        $this->curr_channel=$channel;
        echo This TV Channel is .$this->curr_channel.
;
    }
}

/**执行命令接口
 * Interface ICommand
 */
interface ICommand
{
    function execute();
}

/**开机命令
 * Class CommandOn
 */
class CommandOn implements  ICommand
{
    private $tv;

    public function __construct($tv)
    {
        $this->tv=$tv;
    }

    public function execute()
    {
        $this->tv->turnOn();
    }
}

/**关机命令
 * Class CommandOn
 */
class CommandOff implements  ICommand
{
    private $tv;

    public function __construct($tv)
    {
        $this->tv=$tv;
    }

    public function execute()
    {
        $this->tv->turnOff();
    }
}

/**切换频道命令
 * Class CommandOn
 */
class CommandChannel implements  ICommand
{
    private $tv;
    private $channel;

    public function __construct($tv,$channel)
    {
        $this->tv=$tv;
        $this->channel=$channel;
    }

    public function execute()
    {
        $this->tv->turnChannel($this->channel);
    }
}

/**遥控器
 * Class Control
 */
class Control
{
    private $_onCommand;
    private $_offCommand;
    private $_changeChannel;

    public function __construct($on,$off,$channel)
    {
        $this->_onCommand = $on;
        $this->_offCommand = $off;
        $this->_changeChannel = $channel;
    }

    public function turnOn()
    {
        $this->_onCommand->execute();
    }

    public function  turnOff()
    {
        $this->_offCommand->execute();
    }

    public function changeChannel()
    {
        $this->_changeChannel->execute();
    }
}

Call client code:

header(Content-Type:text/html;charset=utf-8);
//----------------------命令模式--------------------
require_once ./Command/Command.php;
//测试代码
// 命令接收者 　
$myTv = new Tv();
// 开机命令 　
$on = new CommandOn($myTv);
// 关机命令 　
$off = new CommandOff($myTv);

// 频道切换命令 　
$channel = new CommandChannel($myTv, 2);
// 命令控制对象　
$control = new Control($on, $off, $channel);
// 开机 　
$control->turnOn();
// 切换频道 　
$control->changeChannel();
// 关机 　
$control->turnOff();

Applicable scenarios:

1. The system needs to decouple the request caller and the request receiver so that the caller and receiver do not interact directly.

2. The system needs to specify requests, queue requests, and execute requests at different times.

3. The system needs to support the undo (Undo) operation and recovery (Redo) operation of the command.

4. The system needs to combine a group of operations, that is, to support macro commands.

Advantages

1. Reduce the coupling between objects.

2. New commands can be easily added to the system.

3. It is easier to design a combination command.

4. Call the same method to implement different functions

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