smarty加载出现有关问题

smarty加载出现问题
init.inc.php

PHP code

define ( '__ROOT__', str_replace ( '\\', '/', dirname ( __FILE__ ) ) );include 'Ext/Smarty.class.php';class Tpl extends Smarty {    function __construct() {        $this->setTemplateDir ( __ROOT__."/View" );        $this->setCompileDir (__ROOT__."./comp_c" );        $this->left_delimiter = "<{";        $this->right_delimiter = "}>";        parent::__construct();    }}

index.php

PHP code

include 'init.inc.php';class Index extends Tpl {    function index(){        $this->assign('m','asdfasdfasdf');                $this->display('index.html');    }}$tpl = new Index();$tpl->index();

用的Smarty-3.1.11版本 报错信息是:

PHP code

Fatal error: Call to a member function createTemplate() on a non-object in D:\AppServ\www\smarty\Ext\sysplugins\smarty_internal_templatebase.php on line 47

只是我用普通的方法就不会出现问题 比如： 

PHP code

$smarty = new Smarty();$smarty->setTemplateDir ( __ROOT__ . "/View" );$smarty->setCompileDir ( __ROOT__ . "/comp_c" );$smarty -> left_delimiter="<{";$smarty -> right_delimiter="}>";include "init.inc.php";$smarty->display("demo.tpl");

找了一天都没有解决，不知道哪里出现问题 求帮忙…

[解决办法]
你 print_r($this->Smarty); 看看
应该是没有实例化成功，即 $this->Smarty 不是 Smarty 对象