理解依賴注入 for Zend framework 2

依賴注入(Dependency Injection),也成爲控制反轉(Inversion of Control),一種設計模式,其目的是解除類之間的依賴關係。php

假設咱們須要舉辦一個Party,Party須要主持人、廚師、燈光、音響、食品、酒水等等。那麼Party對他們存在依賴關係。用程序語言表示以下:html

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//Party.php
class Party{ //主持人 private $_host;   function __construct(){ include "./Host.php"; $this->_host = new Host(); }   function startParty(){ $this->_host->sayHello(); } }   //Host.php class Host{ private $_name; function sayHello(){ echo "My name is " . $this->_name; } }   //main $party = new Party(); $party->startParty();

可見Party的運行依賴於Host,沒有Host,Party不能單獨運行,也不能單獨發佈爲組件。爲了解除Party對Host的依賴,咱們能夠這麼作:java

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//Party.php
class Party{ //主持人 private $_host;   function __construct($host = ""){ if($host){ $this->_host = $host; } }   function startParty(){ $this->_host->sayHello(); }   function setHost($host){ $this->_host = $host; } }   //Host.php class Host{ private $_name; function sayHello(){ echo "My name is " . $this->_name; } }   //main $host = new Host(); $party = new Party(); $party->setHost($host);//或者 $party = new Party($host) $party->startParty();

此時Party類對Host類的依賴被移到外面,運行時Host類經過構造函數或者setter注入到Party中。Party自己能夠被單獨發 布。若是Host沒有sayHello方法,將其注入到Party中必然致使異常。爲了約束Host必須含有sayHello方法,可使用接口。
laravel

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//Party.php
class Party{ //主持人 private $_hostInterface;   function __construct($host = ""){ if($host){ $this->_hostInterface = $host; } }   function startParty(){ $this->_hostInterface->sayHello(); }   function setHost($host){ $this->_hostInterface = $host; } }   //HostInterface.php Interface HostInterface{ public function sayHello(); }   //Host.php class Host implement HostInterface{ private $_name; function sayHello(){ echo "My name is " . $this->_name; } }   //main $host = new Host(); $party = new Party(); $party->setHost($host);//或者 $party = new Party($host) $party->startParty();

這麼作實際上已經達到了解耦的目的,那麼下面我要把Party全部依賴的廚師、燈光、音響、食品、酒水都加進去,會是怎樣?web

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//Party.php
class Party{ //主持人 private $_host; private $_cooker; private $_wine; private $_food; private $_music; private $_light;   function __construct(){ }   function startParty(){ $this->_host->sayHello(); }   function setHost($host){ $this->_host = $host; }   function setCooker($cooker){ $this->_cooker = $cooker; }   function set Wine($wine){ $this->_wine = $wine; }   //...等等 food, light, music }   ] //Host.php class Host{ private $_name; function sayHello(){ echo "My name is " . $this->_name; } } //Cooker.php class Cooker{} class Wine{} clsas Light{} //...等等其餘類   //main $host = new Host(); $cooker = new Cooker(); $wine = new Wine(); //...等等 $party = new Party(); $party->setHost($host); $party->setCooker($cooker); $party->setWine($wine); $party->setFood($food); $part->setMusic($music); $part->setLight($light); $party->startParty();

代碼中大量的實例化和setter調用,是否能夠優化?咱們須要一個DI容器,在DI中管理各個類,由DI負責注入。此時的DI更像是一個「大工廠模式」。thinkphp

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//Party.php
class Party{ private $_di;   function __construct(){ }   function startParty(){ $this->_di->get("Host")->sayHello(); $this->_di->get("Cooker")->cook(); //... }   function setDI($di){ $this->_di = $di; } }   //HostInterface.php Interface HostInterface{ public function sayHello(); }   //Host.php class Host implement HostInterface{ private $_name; function sayHello(){ echo "My name is " . $this->_name; } }   //main $di = new DI(); //匿名函數形式 $di->set("Host", function(){ return new Host(); }); //類名 $di->set("Cooker", "Path\To\Cooker.php"); //直接返回實例 $di->set("Wine", new Path\To\Wine.php); //數組 $di->set("Light", array("className" => "Path\To\Light"));   $party = new Party(); $party->setDI($di); $party->startParty();

DI使用set來註冊服務類,註冊的方式能夠有不少種,他們都是惰性實例化,set時並不實例化,在get時纔會實例化。而DI在註冊服務類時一般會使用配置來實現,如JSON、XML或者PHP數組。設計模式

DI很是注重約定,$di->get(「Host」)獲取的實例若是不是Host實例的話,將會引起異常。所以,DI屬於強約定模式,一般用 於底層架構,Zend framework 2的核心部分使用DI模式,但在框架應用層使用服務定位模式(ServiceLocator),服務定位模式與依賴注入很是類似,都可以解除類之間的依賴 關係,且實現思路與DI基本一致。數組

參考資料:
理解PHP 依賴注入
話說 依賴注入(DI) or 控制反轉(IoC)
用PHP實現簡單的控制反轉(IOC) 依賴注入(DI),用JSON配置文件架構

本文是做者的團隊博客ComingX上 理解依賴注入 for Zend framework 2 文章的一份拷貝,同爲原創文章。框架

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