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Homephp教程php手册php之依赖注入和控制反转 - yujon


    DI——Dependency Injection   依赖注入

    IoC——Inversion of Control  控制反转

   要想理解上面两个概念,就必须搞清楚如下的问题:

      1、参与者都有谁?  

  答:一般有三方参与者,一个是某个对象;一个是IoC/DI的容器;另一个是某个对象的外部资源。又要名词解释一下,某个对象指的就是任意的、普通的Java对象; IoC/DI的容器简单点说就是指用来实现IoC/DI功能的一个框架程序;对象的外部资源指的就是对象需要的,但是是从对象外部获取的,都统称资源,比如:对象需要的其它对象、或者是对象需要的文件资源等等。

  2、依赖:谁依赖于谁?为什么会有依赖? 

  答:某个对象依赖于IoC/DI的容器。依赖是不可避免的,在一个项目中,各个类之间有各种各样的关系,不可能全部完全独立,这就形成了依赖。传统的开发是使用其他类时直接调用,这会形成强耦合,这是要避免的。依赖注入借用容器转移了被依赖对象实现解耦。

  3、注入:谁注入于谁?到底注入什么?

  答:通过容器向对象注入其所需要的外部资源

  4、控制反转:谁控制谁?控制什么?为什么叫反转?

  答: IoC/DI的容器控制对象,主要是控制对象实例的创建。反转是相对于正向而言的,那么什么算是正向的呢?考虑一下常规情况下的应用程序,如果要在A里面使用C,你会怎么做呢?当然是直接去创建C的对象,也就是说,是在A类中主动去获取所需要的外部资源C,这种情况被称为正向的。那么什么是反向呢?就是A类不再主动去获取C,而是被动等待,等待IoC/DI的容器获取一个C的实例,然后反向的注入到A类中。

  5、依赖注入和控制反转是同一概念吗? 

  答:从上面可以看出:依赖注入是从应用程序的角度在描述,可以把依赖注入描述完整点:应用程序依赖容器创建并注入它所需要的外部资源;而控制反转是从容器的角度在描述,描述完整点:容器控制应用程序,由容器反向的向应用程序注入应用程序所需要的外部资源。

 

     下面我们通过例子来具体看看依赖注入的一些实现方式:

  1.构造器注入

<span style="color: #000000;">php
</span><span style="color: #0000ff;">class</span><span style="color: #000000;"> Book {
   </span><span style="color: #0000ff;">private</span> <span style="color: #800080;">$db_conn</span><span style="color: #000000;">;
 
   </span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">function</span> __construct(<span style="color: #800080;">$db_conn</span><span style="color: #000000;">) {
       </span><span style="color: #800080;">$this</span>->db_conn = <span style="color: #800080;">$db_conn</span><span style="color: #000000;">;
   }
}</span>

  2、setter注入

<span style="color: #000000;">php<br>
  <br>class book{<br>     private $db;<br>   private $file;<br>     function setdb($db){<br>          $this->db=$db;<br>     }<br>     function setfile($file){<br>         $this->file=$file;<br>     }<br>}<br>class file{}<br>class db{}<br>...<br><br>class test{<br></span><span style="color: #800080;">    $book</span> = <span style="color: #0000ff;">new</span><span style="color: #000000;"> Book();
    </span><span style="color: #800080;">$book</span>->setdb(<span style="color: #800080;">new db()</span><span style="color: #000000;">);  <br></span><span style="color: #000000;">      $book->setfile(new file());<br>}
</span>?>

  

  上面俩种方法代码很清晰,但是当我们需要注入很多个依赖时,意味着又要增加很多行,会比较难以管理。

  比较好的解决办法是 建立一个class作为所有依赖关系的container,在这个class中可以存放、创建、获取、查找需要的依赖关系

<span style="color: #000000;">php
</span><span style="color: #0000ff;">class</span><span style="color: #000000;"> Ioc {
   </span><span style="color: #0000ff;">protected</span> <span style="color: #800080;">$db_conn</span><span style="color: #000000;">;
   </span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">function</span><span style="color: #000000;"> make_book() {
       </span><span style="color: #800080;">$new_book</span> = <span style="color: #0000ff;">new</span><span style="color: #000000;"> Book();
       </span><span style="color: #800080;">$new_book</span>->set_db(self::<span style="color: #800080;">$db_conn</span><span style="color: #000000;">);
       </span><span style="color: #008000;">//</span><span style="color: #008000;">...
       //...
       //其他的依赖注入</span>
       <span style="color: #0000ff;">return</span> <span style="color: #800080;">$new_book</span><span style="color: #000000;">;
   }
}</span>

  此时,如果获取一个book实例,只需要执行$newone = Ioc::makebook();

  以上是container的一个具体实例,最好还是不要把具体的某个依赖注入写成方法,采用registry注册,get获取比较好

<span style="color: #000000;">php
</span><span style="color: #0000ff;">class</span><span style="color: #000000;"> Ioc {
</span><span style="color: #008000;">/*</span><span style="color: #008000;">*
* @var 注册的依赖数组
</span><span style="color: #008000;">*/</span>
 
   <span style="color: #0000ff;">protected</span> <span style="color: #0000ff;">static</span> <span style="color: #800080;">$registry</span> = <span style="color: #0000ff;">array</span><span style="color: #000000;">();
 
   </span><span style="color: #008000;">/*</span><span style="color: #008000;">*
    * 添加一个resolve到registry数组中
    * @param  string $name 依赖标识
    * @param  object $resolve 一个匿名函数用来创建实例
    * @return void
    </span><span style="color: #008000;">*/</span>
   <span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">function</span> register(<span style="color: #800080;">$name</span>, Closure <span style="color: #800080;">$resolve</span><span style="color: #000000;">)
   {
      </span><span style="color: #0000ff;">static</span>::<span style="color: #800080;">$registry</span>[<span style="color: #800080;">$name</span>] = <span style="color: #800080;">$resolve</span><span style="color: #000000;">;
   }
 
   </span><span style="color: #008000;">/*</span><span style="color: #008000;">*
     * 返回一个实例
     * @param  string $name 依赖的标识
     * @return mixed
     </span><span style="color: #008000;">*/</span>
   <span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">function</span> resolve(<span style="color: #800080;">$name</span><span style="color: #000000;">)
   {
       </span><span style="color: #0000ff;">if</span> ( <span style="color: #0000ff;">static</span>::registered(<span style="color: #800080;">$name</span><span style="color: #000000;">) )
       {
          </span><span style="color: #800080;">$name</span> = <span style="color: #0000ff;">static</span>::<span style="color: #800080;">$registry</span>[<span style="color: #800080;">$name</span><span style="color: #000000;">];
          </span><span style="color: #0000ff;">return</span> <span style="color: #800080;">$name</span><span style="color: #000000;">();
       }
       </span><span style="color: #0000ff;">throw</span> <span style="color: #0000ff;">new</span> <span style="color: #0000ff;">Exception</span>('Nothing registered with that name, fool.'<span style="color: #000000;">);
   }
   </span><span style="color: #008000;">/*</span><span style="color: #008000;">*
    * 查询某个依赖实例是否存在
    * @param  string $name id
    * @return bool 
    </span><span style="color: #008000;">*/</span>
   <span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">function</span> registered(<span style="color: #800080;">$name</span><span style="color: #000000;">)
   {
      </span><span style="color: #0000ff;">return</span> <span style="color: #008080;">array_key_exists</span>(<span style="color: #800080;">$name</span>, <span style="color: #0000ff;">static</span>::<span style="color: #800080;">$registry</span><span style="color: #000000;">);
   }
}</span>

  现在就可以通过如下方式来注册和注入一个

<span style="color: #000000;">php
</span><span style="color: #800080;">$book</span> = Ioc::registry('book', <span style="color: #0000ff;">function</span><span style="color: #000000;">(){
</span><span style="color: #800080;">$book</span> = <span style="color: #0000ff;">new</span><span style="color: #000000;"> Book;
</span><span style="color: #800080;">$book</span>->setdb('...'<span style="color: #000000;">);
</span><span style="color: #800080;">$book</span>->setprice('...'<span style="color: #000000;">);
</span><span style="color: #0000ff;">return</span> <span style="color: #800080;">$book</span><span style="color: #000000;">;
});
 
</span><span style="color: #008000;">//</span><span style="color: #008000;">注入依赖</span>
<span style="color: #800080;">$book</span> = Ioc::resolve('book'<span style="color: #000000;">);
</span>?>

     

  参考:http://www.4wei.cn/archives/1002316

 

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