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PHP反射原理与用法深入分析

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本文实例讲述了PHP反射原理与用法。分享给大家供大家参考,具体如下:

说到反射,实际上包含两个概念:

PHP官方文档写得很清晰了,下面我就说一下具体的应用。

1.参数检测

有时候需要在函数里需要判断传入的参数类型是否合法。
这时可以使用is_a、is_subclass_of来检测。或者结合反射,做更多检测。

2.动态调用

在依赖注入中,常见到这种用法,比如Laravel5.5中的Container.php

public function build($concrete)
  {
    // If the concrete type is actually a Closure, we will just execute it and
    // hand back the results of the functions, which allows functions to be
    // used as resolvers for more fine-tuned resolution of these objects.
    if ($concrete instanceof Closure) {
      return $concrete($this, $this->getLastParameterOverride());
    }
    $reflector = new ReflectionClass($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()) {
      return $this->notInstantiable($concrete);
    }
    $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.
    $instances = $this->resolveDependencies(
      $dependencies
    );
    array_pop($this->buildStack);
    return $reflector->newInstanceArgs($instances);
  }

上述代码先判断是否是闭包,如果是,直接返回。不是则通过new ReflectionClass($concrete);

生成反射类的实例,然后获取这个类的构造函数和参数,进行初始化的过程。

注意

反射里一个比较重要的用法invoke

当已知这个类的时候,可以通过构造ReflectionMethod来直接调用,如:

class HelloWorld {

  public function sayHelloTo($name) {
    return 'Hello ' . $name;
  }

}

$reflectionMethod = new ReflectionMethod('HelloWorld', 'sayHelloTo');
echo $reflectionMethod->invoke(new HelloWorld(), 'Mike');

当不知道这个类时,知道类的对象,可以用ReflectionObject获取ReflectionMethod后调用,如:

class HelloWorld {

  public function sayHelloTo($name) {
    return 'Hello ' . $name;
  }

}

$hello = new HelloWorld();

$refObj = new ReflectionObject($hello);
$refMethod = $refObj->getMethod('sayHelloTo');
echo $refMethod->invoke($hello,'Mike');

调用流程一般就是获取反射类ReflectionClass/反射对象ReflectionObject的实例,然后获取ReflectionMethod后,invoke。

3.获取注释,生成文档

比如PHPDoc

4.注解,增强版的注释,符合一定的规则

比如某些框架的路由,便是通过注解实现的。

5.不要为了反射而反射

PHP是一门动态语言,其实可以直接通过字符串来调用类或函数,如下:

class HelloWorld {
  public function sayHelloTo($name) {
    return 'Hello ' . $name;
  }
}
$hello = 'HelloWorld';
$helloSay = 'sayHelloTo';
$helloIntance = new $hello;
echo $helloIntance->$helloSay('Mike');

那么为什么还需要反射呢?

希望本文所述对大家PHP程序设计有所帮助。

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