无法在wordpress中添加菜单

    $page_title = "PushBIZ.IN";
    $menu_title = "PushBIZ.IN";
    $capability = 'activate_plugins';
    $menu_slug  = "pushbiz";
    $function   = "PushBIZIN_first";

    add_menu_page( __('Getting Started'), $menu_title, $capability, $menu_slug, array($this, $function), plugins_url( WPPUSH_APPNAME.'/assets/images/app20x20.png' ) ); 
    add_submenu_page( $menu_slug, __('BIZ Message'), __('BIZ Message'), $capability, 'BIZMessage', array($this, 'BIZ_Message') );   
    add_submenu_page( $menu_slug, __('Business Analyst'), __('Business Analyst'), $capability, 'businessanalyst', array($this, 'business_analyst') );
    add_submenu_page( $menu_slug, __('BIZ Interests'), __('BIZ Interests'), $capability, 'BIZinterests', array($this, 'BIZ_interests') );

Warning: call_user_func_array() expects parameter 1 to be a valid callback, first array member is not a valid class name or object in C:\wamp\www\wp\wp-includes\plugin.php on line 525

ADD menu and sub-menu in word-press admin panel -> try this

function jmenu_plugin_top_menu(){
   add_menu_page('My Plugin', 'My Plugin', 'manage_options', __FILE__, 'jmenu_render_plugin_page', plugins_url('/img/icon.png',__DIR__));
   add_submenu_page(__FILE__, 'Custom', 'Custom', 'manage_options', __FILE__.'/custom', 'jmenu_render_custom_page');
   add_submenu_page(__FILE__, 'About', 'About', 'manage_options', __FILE__.'/about', 'jmenu_render_about_page');
 }
 function jmenu_render_plugin_page(){
  ?>
   <div class='wrap'>
    <h2>plugin page</h2>
   </div>
  <?php
 }
 function jmenu_render_custom_page(){
   ?>
   <div class='wrap'>
    <h2>my sub page</h2>
   </div>
   <?php
 }
 function jmenu_render_about_page(){
   ?>
   <div class='wrap'>
    <h2>About my plugin page</h2>
   </div>
   <?php
 }

 add_action('admin_menu','jmenu_plugin_top_menu');

it will add menu and sub-menu in admin panel.

enter image description here

You can also refer this links for adding menu and submenu in admin panel.

http://clivern.com/adding-menus-and-submenus-for-wordpress-plugins/

https://developer.wordpress.org/reference/functions/add_submenu_page/

为了维护方便，把下面的代码封装在插件里了，只要启用插件就可以实现在WordPress后台添加菜单，当然也可以把代码放在主题的functions.php函数里


<?php 
/**
 * Plugin Name: Add a Custom Menu
 * Author: WPScale
 * Description: This is a demo for <a href="#">Add a Custom Menu</a>
 * Author URI: https://wpscale.cn
 * Version:0.0.0
*/
/**
 * Register a custom menu page.
 */

add_action( 'admin_menu', 'add_a_custom_menu' );
function add_a_custom_menu(){
    add_menu_page( 
        __( '在浏览器Tab栏显示', 'textdomain' ),
        '用户自定义主菜单',
        'read',
        'custompage',//在浏览器地址显示的别名
        'custom_menu_page_content',//定义菜单内容的函数
        plugins_url('testplugin/images/logo.jpg' ),5
    ); 

    add_submenu_page(
        'custompage', 
        __('浏览器tab栏子菜单1', 'textdomain'),
        '子菜单1', 
        'read', 
        'submenu1',
        'custom_submenu_page_content',//定义菜单内容的函数
    );
    add_submenu_page(
        'custompage', 
        __('浏览器tab栏子菜单2', 'textdomain'),
        '子菜单2', 
        'read', 
        'submenu2',
        'custom_submenu_page_content',//定义菜单内容的函数
    );
}


/**
 * Display a custom menu page
 */


function custom_menu_page_content(){
    // esc_html_e( '用户自定义菜单内容区', 'textdomain' );    
?>
<?php 
}


function custom_submenu_page_content(){
    esc_html_e( '子菜单内容区', 'textdomain' );    
?>
    <div>
        <label for="">设置</label>
        <select name="" id="">
            <option value="1">1</option>
            <option value="2">2</option>
        </select>
    </div>
<?php 
}
?>

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