Laravel实现构造函数自动依赖注入的方法-华尔子博-奥夏网

Laravel实现构造函数自动依赖注入的方法。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：

<?php

namespace LioHttpControllersForum;

use LioForumRepliesReplyRepository;

use LioForumThreadsThreadCreator;

use LioForumThreadsThreadCreatorListener;

use LioForumThreadsThreadDeleterListener;

use LioForumThreadsThreadForm;

use LioForumThreadsThreadRepository;

use LioForumThreadsThreadUpdaterListener;

use LioHttpControllersController;

use LioTagsTagRepository;

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：

1 2	`$constructor` `=` `$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);

}

具体从容器中获取实例的方法：

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;

}

框架底层通过Reflection反射为开发节省了很多细节，实现了自动依赖注入。这里不做继续深入研究了。

写了一个模拟这个过程的类测试：

<?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;

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