php状态设计模式

状态设计模式的关键就是，环境中拥有所需的全部状态对象，每个状态对象又引用了环境对象；环境对象通过维护一个当前状态属性（用于存放状态对象）从而对所需的全部状态对象产生影响。

下面演示了一个简单的状态设计模式，状态设计模式的核心在于47-49行：

 <?php

 interface Status
 {
     function getProperty();
     function getContext();
 }

 abstract class BaseStatus implements Status
 {
     public $context;

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

     public function getContext()
     {
         return $this->context;
     }
 }

 abstract class BaseContext
 {
     public $currentStatus;

     public function changeStatus(Status $status)
     {
         $this->currentStatus = $status;
     }

     public function statusDetail()
     {
         return $this->currentStatus->getProperty();
     }
 }

 class Context extends BaseContext
 {
     public $status1;
     public $status2;
     public $status3;

     public function __construct()
     {
         $this->status1 = new Status1($this);
         $this->status2 = new Status2($this);
         $this->status3 = new Status3($this);

         $this->currentStatus = $this->status1;
     }
 }

 class Status1 extends BaseStatus
 {
     public function getProperty()
     {
         echo 'I am status1'.PHP_EOL;
         if ($this->getContext()->currentStatus instanceof self) {
             echo 'here is status two and status three<br/>';
             $this->context->status2->getProperty();
             echo '<br/>';
             $this->context->status3->getProperty();
             echo '<br/>';
         }
     }
 }

 class Status2 extends BaseStatus
 {
     public function getProperty()
     {
         echo 'I am status2'.PHP_EOL;
         if ($this->getContext()->currentStatus instanceof self) {
             echo 'here is status one and status three<br/>';
             $this->context->status1->getProperty();
             echo '<br/>';
             $this->context->status3->getProperty();
             echo '<br/>';
         }
     }
 }

 class Status3 extends BaseStatus
 {
     public function getProperty()
     {
         echo 'I am status3'.PHP_EOL;
         if ($this->getContext()->currentStatus instanceof self) {
             echo 'here is status one and status two<br/>';
             $this->context->status1->getProperty();
             echo '<br/>';
             $this->context->status2->getProperty();
             echo '<br/>';
         }
     }
 }

 $context = new Context();

 $context->statusDetail();

 $context->changeStatus($context->status2);

 $context->statusDetail();

 $context->changeStatus($context->status3);

 $context->statusDetail();

运行结果：

I am status1 here is status two and status three
I am status2 
I am status3 
I am status2 here is status one and status three
I am status1 
I am status3 
I am status3 here is status one and status two
I am status1 
I am status2

可见，每次环境对象切换状态的时候，环境对象内的任何修改对于所有状态对象都是同步可见的（状态对象均引用了环境对象）。