MVC模式中使用PHP的控制器的目的是什么?

I am just heading into MVC design pattern. A simple example here does not clear my concept about the use of controller. Could you please explain real use of controller while keeping it simple.

型号:

    class Model {
       public $text;

       public function __construct() {
           $this->text = 'Hello world!';
       }        
    }

控制器:

      class Controller {
          private $model;

          public function __construct(Model $model) {
              $this->model = $model;
          }
      }

查看:

      class View {
         private $model;
         //private $controller;

         public function __construct(/*Controller $controller,*/ Model $model) {
             //$this->controller = $controller;
             $this->model = $model;
         }

          public function output() {
               return '<h1>' . $this->model->text .'</h1>';
         }

      }

索引:

      require_once('Model.php'); 
      require_once('Controller.php');
      require_once('View.php');

      //initiate the triad
      $model = new Model();
      //It is important that the controller and the view share the model
      //$controller = new Controller($model);
      $view = new View(/*$controller,*/ $model);
      echo $view->output();

推荐答案

MVC 模式中控制器的目的是改变模型层的状态.

class Account extends ComponentsController
{

    private $recognition;

    public function __construct(ModelServicesRecognition $recognition)
    {
        $this->recognition = $recognition;
    }

    public function postLogin($request)
    {    
        $this->recognition->authenticate(
            $request->getParameter('credentials'),
            $request->getParameter('method')
        );
    }

    // other methods
    
}