本文实例讲述了对PHP依赖注入的理解。分享给大家供大家参考，具体如下：
看Laravel的IoC容器文档只是介绍实例，但是没有说原理，之前用MVC框架都没有在意这个概念，无意中在phalcon的文档中看到这个详细的介绍，感觉豁然开朗，复制粘贴过来，主要是好久没有写东西了，现在确实很懒变得！
首先，我们假设，我们要开发一个组件命名为SomeComponent。这个组件中现在将要注入一个数据库连接。
在这个例子中，数据库连接在component中被创建，这种方法是不切实际的，这样做的话，我们将不能改变数据库连接参数及数据库类型等一些参数。
class SomeComponent { /** * The instantiation of the connection is hardcoded inside * the component so is difficult to replace it externally * or change its behavior */ public function someDbTask() { $connection = new Connection(array( "host" => "localhost", "username" => "root", "password" => "secret", "dbname" => "invo" )); // ... }}$some = new SomeComponent();$some->someDbTask();
为了解决上面所说的问题，我们需要在使用前创建一个外部连接，并注入到容器中。就目前而言，这看起来是一个很好的解决方案：
class SomeComponent { protected $_connection; /** * Sets the connection externally */ public function setConnection($connection) { $this->_connection = $connection; } public function someDbTask() { $connection = $this->_connection; // ... }}$some = new SomeComponent();//Create the connection$connection = new Connection(array( "host" => "localhost", "username" => "root", "password" => "secret", "dbname" => "invo"));//Inject the connection in the component$some->setConnection($connection);$some->someDbTask();
现在我们来考虑一个问题，我们在应用程序中的不同地方使用此组件，将多次创建数据库连接。使用一种类似全局注册表的方式，从这获得一个数据库连接实例，而不是使用一次就创建一次。
class Registry{ /** * Returns the connection */ public static function getConnection() { return new Connection(array( "host" => "localhost", "username" => "root", "password" => "secret", "dbname" => "invo" )); }}class SomeComponent{ protected $_connection; /** * Sets the connection externally */ public function setConnection($connection){ $this->_connection = $connection; } public function someDbTask() { $connection = $this->_connection; // ... }}$some = new SomeComponent();//Pass the connection defined in the registry$some->setConnection(Registry::getConnection());$some->someDbTask();
现在，让我们来想像一下，我们必须在组件中实现两个方法，首先需要创建一个新的数据库连接，第二个总是获得一个共享连接：
class Registry{ protected static $_connection; /** * Creates a connect<a>2本文来源gao*daima.com搞@代#码&网6</a><pre>搞gaodaima代码
ion */ protected static function _createConnection() { return new Connection(array( "host" => "localhost", "username" => "root", "password" => "secret", "dbname" => "invo" )); } /** * Creates a connection only once and returns it */ public static function getSharedConnection() { if (self::$_connection===null){ $connection = self::_createConnection(); self::$_connection = $connection; } return self::$_connection; } /** * Always returns a new connection */ public static function getNewConnection() { return self::_createConnection(); }}class SomeComponent{ protected $_connection; /** * Sets the connection externally */ public function setConnection($connection){ $this->_connection = $connection; } /** * This method always needs the shared connection */ public function someDbTask() { $connection = $this->_connection; // … } /** * This method always needs a new connection */ public function someOtherDbTask($connection) { }}$some = new SomeComponent();//This injects the shared connection$some->setConnection(Registry::getSharedConnection());$some->someDbTask();//Here, we always pass a new connection as parameter$some->someOtherDbTask(Registry::getConnection());
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