php - 为什么 isset() 总是在自定义对象上返回 FALSE

Question

我无法理解这种行为:我的 isset() 检查总是在具有确定值的 property 上返回 false!

<?php

  class User {
    protected $userId; // always filled
    protected $userName; // always filled

    /**
     * Magic method for the getters.
     * 
     * @param type $property
     * @return \self|property
     */
    public function __get($property) {
        if (property_exists($this, $property)) {
            return $this->$property;
        } else {
            throw new Exception('property '.$property.' does not exist in '.__CLASS__.' class');
        }
    }

  }

?>

当我使用以下代码从另一个类检查此变量时:

isset($loggedUser->userName); // loggedUser is my instantiation of the User.php

它返回FALSE？？但是当我在我的 User.php 中重载 __isset() 函数时，我得到了 TRUE ，正如我预期的那样:

public function __isset($name)
{
    return isset($this->$name);
}

明确一点:

echo $loggedUser->name;   // result "Adis"
isset($loggedUser->name); // results in FALSE, but why?

感谢您的帮助!

Answer 1

protected 属性仅在对象的方法中可见。它们对外部访问是隐藏的。

---

class prot_text {
    protected $cannot_see_me;
    function see_me() {
       echo $this->cannot_see_me;
    }
}

$x = new prot_text();
echo $x->cannot_see_me; // does not work - accessing from "outside"
$x->see_me(); // works, accessing the attribute from "inside".