源码-反转控制的理解

源码-反转控制的理解

反转控制是什么，有什么用：反转控制为Ioc Container，简称ICO，解决各个类之间的依赖问题。主流框架(laravel、yii等)源码均有出现，若不能理解反转控制，对源码的理解就很难深入。

• 功能是什么
  1、存储定义的类
  2、实例化类

---

案例说明-简易案例

//容器类，封装的很简单，set方法用于存储类，get用于实例化类
Class Container
{
    private $_definitions;

//定义类
    public function set($class, $definition)
    {
        $this->_definitions[$class] = $definition;
    }

//实例化类  call_user_func：第一个参数 callback 是被调用的回调函数，其余参数是回调函数的参数。
    public function get($class, $params = [])
    {
        $definition = $this->_definitions[$class];
        return call_user_func($definition, $params);
    }
}
//构造赋值属性
class EmailSenderBy163
{
    private $_name;

    public function __construct($name = '')
    {
        $this->_name = $name;
    }

    public function send()
    {
    }
}


$container = new Container;
$container->set('EmailSenderBy163', function ($name = '') {
//函数追加new自己函数
    return new EmailSenderBy163($name);
});
//启动new函数new自己
$emailSenderBy163 = $container->get('EmailSenderBy163', '163');

echo "<pre>";
print_r($emailSenderBy163);

//打印出来的结果
EmailSenderBy163 Object
(
    [_name:EmailSenderBy163:private] => 163
)

上述不太好理解，我还用思维导图做了图让你理解，绝对贴心

案例说明-复杂案例

//没什么好说，一个类构造赋值属性
class EmailSenderBy163
{
    private $_name;

    public function __construct($name = '')
    {
        $this->_name = $name;
    }

    public function send()
    {
    }
}

class User
{
    private $_emailSenderObject;

    //构造赋值并限制$emailSenderObject为EmailSenderBy163 类和子类为
    public function __construct(EmailSenderBy163 $emailSenderObject)
    {
        $this->_emailSenderObject = $emailSenderObject;
    }

    public function register()
    {
        $this->_emailSenderObject->send();
    }
}
//容器
Class Container
{
    private $_definitions;

    public function set($class, $definition)
    {
        $this->_definitions[$class] = $definition;
    }

    public function get($class, $params = [])
    {
    //get方法在判断回调函数上更加严谨
        if (isset($this->_definitions[$class]) && is_callable($this->_definitions[$class], true)) {
            $definition = $this->_definitions[$class];
            //$this是指这个容器
            return call_user_func($definition, $this, $params);
        } else {
            throw new Exception("error");
        }
    }
}


$container = new Container;

$container->set('EmailSenderBy163', function ($container, $name = '') {
    return new EmailSenderBy163($name);
});
$container->set('User', function ($container, $params = []) {
//$container对应上述的$this，这样拿到相对应参数，这里有点绕想想会明白的
    return new User($container->get($params[0], $params[1]));
});

echo '<pre>';
print_r($container->get('EmailSenderBy163', ['163']));
print_r($container->get('User', ['EmailSenderBy163', '163']));

这就是反转控制，需要先把所有的类全部set进去，然后get的时候指定其所依赖的类，依然很麻烦。可以考虑使用反射，并做自动实例化处理。
反射类地址：http://php.net/manual/zh/book.reflection.php

利用反射增加容器类

Class Container
{
    public function get($class, $params = [])
    {
        return $this->build($class, $params);
    }

    public function build($class, $params)
    {
        $dependencies = [];
    //实例化反射类
        $reflection = new ReflectionClass($class);
        //获取类的构造函数
        $constructor = $reflection->getConstructor();
        if ($constructor !== null) {
        //获取参数
            foreach ($constructor->getParameters() as $param) {
            //获得类的提示类型
                $c = $param->getClass();
                if ($c !== null) {
                //获取类名
                    $dependencies[] = $this->get($c->getName(), $params);
                }
            }
        }

        foreach ($params as $index => $param) {
            $dependencies[$index] = $param;
        }
//从给出的参数创建一个新的类实例
        return $reflection->newInstanceArgs($dependencies);
    }
}

$container = new Container;
$user = $container->get('User');
echo '<pre>';
print_r($user);

输出结果

User Object
(
    [_emailSenderObject:User:private] => EmailSenderBy163 Object
        (
            [_name:EmailSenderBy163:private] => 
        )

)