什么是状态设计模式

类图如下：

状态设计模式

这个可以理解为对象行为随着状态改变的一个设计模式

如，随着四季变化，树的行为也跟着变化。

随着开关的变化，灯泡的行为也跟着变化。

为什么要使用

在软件设计过程中，对象的状态可能是会发生改变的，当对象的状态改变之后，我们可以使用 if 或者 switch 语句来判断对象的行为，但是如果对象的状态特别多的话，就会发生一个问题，对象的状态增加修改之后会频繁修改原来的类。

使用状态设计模式时，允许一个对象在其内部状态改变时改变它的行为。

类型

行为型模式

参与者

• Context 上下文类

  • 维护一个具体状态角色ConcreteState的实例，这个实例定义当前状态。

• IState 抽象状态类

  • 声明了各种不同状态对应的方法。

• ConcreteState 具体状态类

  • 每一个实现一个与Context的一个状态相关的行为。

例子

只有两种状态的灯泡

代码中 Light 代表 Context 上下文类

<?php

/**
 * 只有两种状态的灯泡，可以开启和关闭
 */

/**
 * 灯
 */
class Light
{
    private $offState;
    private $onState;

    /**
     * @var IState
     */
    private $currentState;

    public function __construct()
    {
        $this->offState = new offState($this);
        $this->onState = new onState($this);
        $this->currentState = $this->offState;
    }

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

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

    public function setState(IState $state)
    {
        $this->currentState = $state;
    }

    public function getOnState()
    {
        return $this->onState;
    }

    public function getOffState()
    {
        return $this->offState;
    }
}

interface IState
{
    public function turnOn();

    public function turnOff();
}

/**
 * 灯的关闭状态
 */
class offState implements IState
{
    private $context;

    public function __construct(Light $light)
    {
        $this->context = $light;
    }

    public function turnOff()
    {
        echo 'light is already **off**, please chose another operation'.PHP_EOL;
    }

    public function turnOn()
    {
        echo 'light on!'.PHP_EOL;
        $this->context->setState($this->context->getOnState());
    }
}

/**
 * 灯的开启状态
 */
class onState implements IState
{
    private $context;

    public function __construct(Light $light)
    {
        $this->context = $light;
    }

    public function turnOff()
    {
        echo 'light off!'.PHP_EOL;
        $this->context->setState($this->context->getOffState());
    }

    public function turnOn()
    {
        echo 'light is already **on**, please chose another operation'.PHP_EOL;
    }
}

class Client
{
    private $light;

    public function __construct()
    {
        $this->light = new Light();
        $this->light->turnOn();
        $this->light->turnOn();
        $this->light->turnOff();
        $this->light->turnOff();
    }
}

$client = new Client();

新增加一种损坏状态

<?php

// 状态模式设计方法

/**
 * 灯
 */
class Light
{
    private $offState;
    private $onState;
    private $brokenState;

    /**
     * @var IState
     */
    private $currentState;

    public function __construct()
    {
        $this->offState = new offState($this);
        $this->onState = new onState($this);
        $this->brokenState = new brokenState();
        $this->currentState = $this->offState;
    }

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

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

    public function brokeIt()
    {
        $this->currentState->turnBroken();
    }

    public function setState(IState $state)
    {
        $this->currentState = $state;
    }

    public function getOnState()
    {
        return $this->onState;
    }

    public function getOffState()
    {
        return $this->offState;
    }

    public function getBrokeState()
    {
        return $this->brokenState;
    }
}

interface IState
{
    public function turnOn();

    public function turnOff();

    public function turnBroken();
}

/**
 * 灯的关闭状态
 */
class offState implements IState
{
    private $context;

    public function __construct(Light $light)
    {
        $this->context = $light;
    }

    public function turnOff()
    {
        echo 'light is already **off**, please chose another operation'.PHP_EOL;
    }

    public function turnOn()
    {
        echo 'light on!'.PHP_EOL;
        $this->context->setState($this->context->getOnState());
    }

    public function turnBroken()
    {
        echo 'light is broke now'.PHP_EOL;
        $this->context->setState($this->context->getBrokeState());
    }
}

/**
 * 灯的开启状态
 */
class onState implements IState
{
    private $context;

    public function __construct(Light $light)
    {
        $this->context = $light;
    }

    public function turnOff()
    {
        echo 'light off!'.PHP_EOL;
        $this->context->setState($this->context->getOffState());
    }

    public function turnOn()
    {
        echo 'light is already **on**, please chose another operation'.PHP_EOL;
    }

    public function turnBroken()
    {
        echo 'light broken now'.PHP_EOL;
        $this->context->setState($this->context->getBrokeState());
    }
}

/**
 * 新增一个损坏状态
 *
 * Class brokenState
 */
class brokenState implements IState
{
    public function turnOn()
    {
        echo 'light is broken, can not open now'.PHP_EOL;
    }

    public function turnOff()
    {
        echo 'light is already off, because it is broken.'.PHP_EOL;
    }

    public function turnBroken()
    {
        echo 'light is already broken.'.PHP_EOL;
    }
}

/**
 * Class Client
 */
class Client
{
    private $light;

    public function __construct()
    {
        $this->light = new Light();
        $this->light->turnOn();
        $this->light->turnOn();
        $this->light->turnOff();
        $this->light->turnOff();
        $this->light->brokeIt();
        $this->light->turnOn();
        $this->light->turnOff();
    }
}

$client = new Client();

light on!
light is already **on**, please chose another operation
light off!
light is already **off**, please chose another operation
light is broke now
light is broken, can not open now
light is already off, because it is broken.