Understanding Dependency Injection (Dependency injection)

Understanding Dependency Injection

Yii2.0 uses the idea of dependency injection. It is using this mode that makes YII2 exceptionally flexible and powerful. Do not think this is a very iffy thing, read the following two examples to understand.

classsessionstorage{function__construct ($cookieName= ' php_sess_id ')  {    Session_name($cookieName); Session_Start(); }  functionSet$key,$value)  {    $_session[$key] =$value; }  functionGet$key)  {    return $_session[$key]; }  // ...}

This is an operation session class, the following user class to use the function in the session

classuser{protected $storage; function__construct () {$this->storage =NewSessionstorage (); }  functionSetLanguage ($language)  {    $this->storage->set (' Language ',$language); }  functionGetLanguage () {return $this->storage->get (' language '); }  // ...}

We can call it that way.

$user New User (); $user->setlanguage (' zh ');

This doesn't seem to be a problem, but the user has written the Sessionstorage class, the coupling is too strong, not flexible enough to be decoupled.

Optimized user Class Code

classuser{protected $storage; function__construct ($storage)  {    $this->storage =$storage; }  functionSetLanguage ($language)  {    $this->storage->set (' Language ',$language); }  functionGetLanguage () {return $this->storage->get (' language '); }  // ...}

Call Method:

$storage New Sessionstorage (' session_id '); $user New User ($storage);

Instead of creating a Sessionstorage object in the user class, the storage object is passed as a parameter to the user's constructor, which is dependency injection .

The way of dependency injection

Dependency injection can be done in three different ways:

Constructor Injection Constructor Injection

This is also the most common one that has just been used:

class user{  function __construct ($storage)  {    $this$ Storage;  }   //  ...}

Set Value injection Setter injection

class user{  function setsessionstorage ($storage)  {    $this  $storage;  }   //  ...}

Attribute Injected Property Injection

class user{  public$sessionStorage;} $user $storage;

Here's an example of Yii2.

// Create a Pagination object with the total count $pagination New $count ]); // limit the query using the pagination and retrieve the articles $articles $query->offset ($pagination,offset)    ->limit ($pagination ,limit)    ->all ();

Reference: http://fabien.potencier.org/what-is-dependency-injection.html

Understanding Dependency Injection (Dependency injection)