后端开发|php教程
Laravel,构造函数,自动依赖注入
后端开发-php教程
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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：
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threads = $threads; $this->tags = $tags; $this->threadCreator = $threadCreator; $this->replies = $replies; }}
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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 constructors 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：
kulou = $kulou; $this->junjun = $junjun; }}//$tanteng = new tanteng(new kulou(),new junjun());$reflector = new ReflectionClass( anteng);$constructor = $reflector->getConstructor();$dependencies = $constructor->getParameters();print_r($dependencies);exit;
原理是通过ReflectionClass类解析类的构造函数，并且取出构造函数的参数，从而判断依赖关系，从容器中取，并自动注入。
转自：小谈博客 //01/laravel-construct-ioc/
更多关于Laravel相关内容感兴趣的读者可查看本站专题：《Laravel框架入门与进阶教学》、《php优秀开发框架总结》、《smarty模板入门基础教学》、《php日期与时间用法总结》、《php面向对象程序设计入门教学》、《php字符串(string)用法总结》、《php+mysql数据库操作入门教学》及《php常见数据库操作技巧汇总》
