为了将数据从一个对象检索到另一个对象，您应该创建返回特定数据的方法。

class controller{
    private $hello;
    public function setHello(){
        $this->hello = 'hi';
    }
    public function getHello(){
        return $this->hello;
    }
 }
 class model{
     public function helloWorld(){
         $controller = new controller();
         $controller->setHello();
         $hello = $controller->getHello();
     }
 }

还要注意，从模型中启动控制器并不常见，例如MVC。所以在上面的例子中，基本上模型应该是控制器，反之亦然。

如果你想从类中获得一个变量（如你所说），那么你正在寻找static关键字：

class Controller {
    static $hello = "Hello world";
}
class Model {
    public function helloworld() {
        echo Controller::$hello;
    }
}
$model = new Model();
$model->helloworld();

如果你的意思是"我想创建一个Controller对象，并让Model对象能够从该控制器读取消息，那么你正在寻找这个：

class Controller {
    public function hello() {
        return "Hello world";
    }
}
class Model {
    public function helloworld($controller) {
        echo $controller->hello();
    }
}
$controller = new Controller();
$model = new Model();
$model->helloworld($controller);

您的类没有名称？

在controller.php中

<?PHP
class Controller{
    public static function hello () {
        $hello = "Hello World!";
        #when you call a function, you need to say what it must return!
        return $hello;
    }
}
?>

在model.php中

<?php
class Model extends Controller {
   public static function helloworld() {
     #call the function inside the controller class. class::function();
     $text = Controller::hello();
     #tell what to do, you can use echo or return.
     return $text;
   }
}
?>

在index.php中

<?PHP
include "controller.php";
include "model.php";
#include everything you need
#use class:function();
echo Model::helloworld();