在PHP中为什么不起作用

Question

class GrandClass {
    public $data;
    public function __construct() {
        $this->someMethodInTheParentClass();
    }
    public function someMethodInTheParentClass() {
        $this->$data = 123456;
    }
}

class MyParent extends GrandClass{
    public function __construct() {
        parent::__construct();
    }
}

class Child extends MyParent {
    // public $data;
    public function __construct() {
        parent::__construct();
    }
    public function getData() {
        return $this->data; 
    }
}

$a = new Child();
var_dump($a->getData());

PHP注意：未定义的变量：第7行的D：\ test.php中的数据

PHP致命错误：无法访问第7行的D：\ test.php中的空属性

Answer 1

使用$ this-＆gt; data = 123456更新你的函数someMethodInTheParentClass：

 public function someMethodInTheParentClass() {
        $this->data = 123456;
    }

Answer 2

Use  `$this->data = 123456; `instead of`  $this->$data = 123456;` in below function

public function someMethodInTheParentClass() {
        $this->data = 123456;
}