PHP致命错误:无法访问空属性 [英] PHP Fatal error: Cannot access empty property

问题描述

我是php的新手，我已经执行了以下代码.

I'm new to php and I have executed below code.

<?php
class my_class{

    var $my_value = array();
    function my_class ($value){
        $this->my_value[] = $value;
    }
    function set_value ($value){
    // Error occurred from here as Undefined variable: my_value
        $this->$my_value = $value;

    }

}

$a = new my_class ('a');
$a->my_value[] = 'b';
$a->set_value ('c');
$a->my_class('d');

foreach ($a->my_value as &$value) {
    echo $value;
}

?>

我遇到了以下错误.可能是什么错误?

I got below errors. What could be the error?

Notice: Undefined variable: my_value in C:\xampp\htdocs\MyTestPages\f.php on line 15

Fatal error: Cannot access empty property in C:\xampp\htdocs\MyTestPages\f.php on line 15

推荐答案

您以错误的方式访问属性.使用$this->$my_value = ..语法，可以使用$ my_value中的值名称设置属性.您想要的是$this->my_value = ..

You access the property in the wrong way. With the $this->$my_value = .. syntax, you set the property with the name of the value in $my_value. What you want is $this->my_value = ..

$var = "my_value";
$this->$var = "test";

与

$this->my_value = "test";

要解决示例中的一些问题，下面的代码是一种更好的方法

To fix a few things from your example, the code below is a better aproach

class my_class {

    public  $my_value = array();

    function __construct ($value) {
        $this->my_value[] = $value;
    }

    function set_value ($value) {
        if (!is_array($value)) {
            throw new Exception("Illegal argument");
        }

        $this->my_value = $value;
    }

    function add_value($value) {
        $this->my_value = $value;
    }
}

$a = new my_class ('a');
$a->my_value[] = 'b';
$a->add_value('c');
$a->set_value(array('d'));

这确保my_value不会在调用set_value时将其类型更改为字符串或其他类型.但是您仍然可以直接设置my_value的值，因为它是公共的.最后一步是将my_value设为私有，并且仅通过getter/setter方法访问my_value

This ensures, that my_value won't change it's type to string or something else when you call set_value. But you can still set the value of my_value direct, because it's public. The final step is, to make my_value private and only access my_value over getter/setter methods

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