oop classe per directory

[rickystra]

ciao, sto sperimentando la programmazione ad oggetti ma ho questo problema:

<?php
class my_directory
{
    public $mydir;
    public function _construct($mydir)
    {
        $this->mydir = $mydir;
    }
    public function get_dir()
    {
        if ($handle = opendir($this->mydir))
        {
            while (false !== ($file = readdir($handle)))
            {
                if ($file != "." && $file != "..")
                {
                    $arr[] = $file;
                    sort($arr);
                }
            }
            closedir($handle);
        }
    return $arr;
    }
}


$categorie = new my_directory('games');
$tree = $categorie->get_dir();
var_dump($tree);
?>

ottengo NULL
perchè?