discuz post_image_btn_extra and post_image_tab_extra are invalid?

I want to make a discuz plug-in. I followed the tutorial and did the test:

<code class="php">    if(!defined('IN_DISCUZ')) {
        exit('Access Denied');
    }
    class plugin_tutu{
        function post_image_btn_extra(){
            return "aaa";
        }
        function post_image_tab_extra(){
            return "sss";
        }
    }</code>

But there was no response.
Then I replaced post_image_btn_extra with global_usernav_extra1, but it was successfully output at the corresponding location!

Reply content:

I want to make a discuz plug-in. I followed the tutorial and did the test:

<code class="php">    if(!defined('IN_DISCUZ')) {
        exit('Access Denied');
    }
    class plugin_tutu{
        function post_image_btn_extra(){
            return "aaa";
        }
        function post_image_tab_extra(){
            return "sss";
        }
    }</code>

But there was no response.
Then I replaced post_image_btn_extra with global_usernav_extra1, but it was successfully output at the corresponding location!

In the end no one answered my question...Finally I found the solution myself...

<code>if(!defined('IN_DISCUZ')) {
    exit('Access Denied');
}
class plugin_tutu{
    
}
class plugin_tutu_forum extends plugin_tutu{
        function  post_image_btn_extra(){
        return "aaa";
    }
    function post_image_tab_extra(){
        return 'sss';
    }
}</code>