本文實例講述了Laravel實現構造函數自動依賴注入的方法。分享給大家供大家參考，具體如下：
在Laravel的構造函數中可以實現自動依賴注入，而不需要實例化之前先實例化需要的類，如代碼所示：
<?php
namespace Lio\Http\Controllers\Forum;
use Lio\Forum\Replies\ReplyRepository;
use Lio\Forum\Threads\ThreadCreator;
use Lio\Forum\Threads\ThreadCreatorListener;
use Lio\Forum\Threads\ThreadDeleterListener;
use Lio\Forum\Threads\ThreadForm;
use Lio\Forum\Threads\ThreadRepository;
use Lio\Forum\Threads\ThreadUpdaterListener;
use Lio\Http\Controllers\Controller;
use Lio\Tags\TagRepository;
class ForumThreadsController extends Controller implements ThreadCreatorListener, ThreadUpdaterListener, ThreadDeleterListener
{
protected $threads;
protected $tags;
protected $currentSection;
protected $threadCreator;
public function __construct(
ThreadRepository $threads,
ReplyRepository $replies,
TagRepository $tags,
ThreadCreator $threadCreator
) {
$this->threads = $threads;
$this->tags = $tags;
$this->threadCreator = $threadCreator;
$this->replies = $replies;
}
}
注意構造函數中的幾個類型約束，其實並沒有地方實例化這個Controller並把這幾個類型的參數傳進去，Laravel會自動檢測類的構造函數中的類型約束參數，並自動識別是否初始化並傳入。
源碼vendor/illuminate/container/Container.php中的build方法：
$constructor = $reflector->getConstructor(); dump($constructor);
這裡會解析類的構造函數，在這裡打印看：
它會找出構造函數的參數，再看完整的build方法進行的操作：
public function build($concrete, array $parameters = [])
{
// If the concrete type is actually a Closure, we will just execute it and
// hand back the results of the functions, which allows functions to be
// used as resolvers for more fine-tuned resolution of these objects.
if ($concrete instanceof Closure) {
return $concrete($this, $parameters);
}
$reflector = new ReflectionClass($concrete);
// If the type is not instantiable, the developer is attempting to resolve
// an abstract type such as an Interface of Abstract Class and there is
// no binding registered for the abstractions so we need to bail out.
if (! $reflector->isInstantiable()) {
$message = "Target [$concrete] is not instantiable.";
throw new BindingResolutionContractException($message);
}
$this->buildStack[] = $concrete;
$constructor = $reflector->getConstructor();
// If there are no constructors, that means there are no dependencies then
// we can just resolve the instances of the objects right away, without
// resolving any other types or dependencies out of these containers.
if (is_null($constructor)) {
array_pop($this->buildStack);
return new $concrete;
}
$dependencies = $constructor->getParameters();
// Once we have all the constructor's parameters we can create each of the
// dependency instances and then use the reflection instances to make a
// new instance of this class, injecting the created dependencies in.
$parameters = $this->keyParametersByArgument(
$dependencies, $parameters
);
$instances = $this->getDependencies(
$dependencies, $parameters
);
array_pop($this->buildStack);
return $reflector->newInstanceArgs($instances);
}
具體從容器中獲取實例的方法：
protected function resolveClass(ReflectionParameter $parameter)
{
try {
return $this->make($parameter->getClass()->name);
}
// If we can not resolve the class instance, we will check to see if the value
// is optional, and if it is we will return the optional parameter value as
// the value of the dependency, similarly to how we do this with scalars.
catch (BindingResolutionContractException $e) {
if ($parameter->isOptional()) {
return $parameter->getDefaultValue();
}
throw $e;
}
}
框架底層通過Reflection反射為開發節省了很多細節，實現了自動依賴注入。這裡不做繼續深入研究了。
寫了一個模擬這個過程的類測試：
<?php
class kulou
{
//
}
class junjun
{
//
}
class tanteng
{
private $kulou;
private $junjun;
public function __construct(kulou $kulou,junjun $junjun)
{
$this->kulou = $kulou;
$this->junjun = $junjun;
}
}
//$tanteng = new tanteng(new kulou(),new junjun());
$reflector = new ReflectionClass('tanteng');
$constructor = $reflector->getConstructor();
$dependencies = $constructor->getParameters();
print_r($dependencies);exit;
原理是通過ReflectionClass類解析類的構造函數，並且取出構造函數的參數，從而判斷依賴關系，從容器中取，並自動注入。
轉自：小談博客 http://www.tantengvip.com/2016/01/laravel-construct-ioc/
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