Laravel实现构造函数自动依赖注入的方法

本文实例讲述了Laravel实现构造函数自动依赖注入的方法。分享给大家供大家参考，具体如下：

在Laravel的构造函数中可以实现自动依赖注入，而不需要实例化之前先实例化需要的类，如代码所示：

<?phpnamespace 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; }}

注意构造函数中的几个类型约束，其实并没有地方实例化这个Controller并把这几个类型的参数传进去，Laravel会自动检测类的构造函数中的类型约束参数，并自动识别是否初始化并传入。

源码vendor/illuminate/container/Container.php中的build方法：

$constructor = $reflector->getConstructor();dump($constructor);

这里会解析类的构造函数，在这里打印看：

它会找出构造函数的参数，再看完整的build方法进行的操作：

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);}