使用PHP无法在wordpress插件中显示类变量

Question

I am working on a WordPress plugin and started working with classes to store information such as database settings. I have however run into a problem. I cannot output or echo the variables inside my classes. I created another test plugin just to test certain concepts. This is the plugin code from my test plugin to test classes:

<?php
/* WordPress Plugin */
//  create class
class test
{
    //  Variable
    public $HW = "HELLO WORLD!";

    //  Function to return variable
    public function getHW()
    {
         return $this->HW;
    }

    //  Function to set variable
    public function setHW($newHW)
    {
         $this->HW = $newHW;
    }
}

//  Initiate class
$classObj = new test();

//  Output data
function displayClass()
{
    echo "hello world!";
    echo $classObj->getHW();
}

//  Add code to display in wordpress
add_shortcode('test_hw', 'displayClass');
?>

I know that the wordpress section works because 'hello world!' displays on the page. However I cannot get the variables inside the class to load. It either prevents the page from loading or it doesn't display the variable. I cannot seem to find the error. Any help would be appreciated.

I have even tried code like this:

$classObj = new test();
$testHW = $classObj->getHW();

and

$classObj = new test();
$testHW = $classObj->HW;

Neither of these options work either. I am running Apache 2.4.6 with PHP 5.5.7 on Fedora 19.

Answer 1

I don't think $classObj is available in the function, because it is instantiated outside it. You could try making $classObj global. It is not a recommended solution, but it seems to be a normal solution in WordPress. Try this code:

<?php
/* WordPress Plugin */
//  create class
class test
{
    //  Variable
    public $HW = "HELLO WORLD!";

    //  Function to return variable
    public function getHW()
    {
         return $this->HW;
    }

    //  Function to set variable
    public function setHW($newHW)
    {
         $this->HW = $newHW;
    }
}

//  Initiate class
global $classObj;
$classObj = new test();

//  Output data
function displayClass()
{
    global $classObj;
    echo "hello world!";
    echo $classObj->getHW();
}

displayClass();
?>