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

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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] =>         ))