Question

I am trying to make a class in PHP that will need to use a function from WordPress, but the function doesn’t work inside the class. Is there a way to make it work? Thanks!

class MetaData
{   
    private $key;

    public function __construct($key){
        $this->key = get_post_meta($post->ID, $key, TRUE); 
    }
    public function getData(){
        print $this->key;
    }
}

Answer 1

$post is a global variable, so you have to to explicitly state that:

public function __construct ($key) {
    global $post;
    $this->key = get_post_meta($post->ID, $key, TRUE); 
}