call_user_func_array() expects parameter 1 to be a valid callback, array must have exactly two members

Question

I am trying to create a theme option page in my plugin. I have pasted below the entire code. But it is giving an error :

call_user_func_array() expects parameter 1 to be a valid callback, array must have exactly two members

class KD_Options {

    public function __construct(){
        $this->register_settings_and_fields();
    }

    public function add_menu_page(){
        add_options_page('Theme Options','Theme Options','administrator',__FILE__, array('KD_Options'),'display_options_page'); 
    }

    public function display_options_page(){
        ?>
        <div class="wrap">
            <h2>My theme Options</h2>
            <form method="post" action="options.php" enctype="multipart/form-data">
                <?php settings_fields('kd_plugin_options');//includes all the hidden fields for security ?>
                <?php do_settings_sections(__FILE__); ?>
            </form>
        </div>
        <?php               
    }

    public function register_settings_and_fields(){
        register_setting('kd_plugin_options','kd_plugin_options');//3rd parameter = optional cb
        //get_option('kd_plugin_options');  
        add_settings_section('kd_main_section', 'Main Settings', array($this, 'kd_main_section_cb'), __FILE__);//id, title of section, cb, which page?
        add_settings_field('kd_banner_heading','Banner Heading', array($this, 'kd_banner_heading_setting'), __FILE__, 'kd_main_section');
        add_settings_field('kd_logo','Your Logo: ', array($this, 'kd_logo_setting'), __FILE__, 'kd_main_section');
    }

    /*
     *
     * Inputs
     *
     */

     // Banner Heading
     public function kd_banner_heading_setting() {
         echo '<input>';
     }

     // Logo
     public function kd_logo_setting() {
         echo '<input type="file">';
     }

     //Function for validation and sanitization
     public function kd_main_section_cb(){
         //optional
     }

}

add_action('admin_menu', function(){
    KD_Options::add_menu_page();
});

add_action('admin_init', function(){
    new KD_Options();
});

I guess there is some issue with add_settings_section where the kd_main_section_cb is not getting called or something. I am having some trouble debugging the script. So, if anyone can help me out by letting me know what is the issue.

Answer 1

The parameters are fairly wrong here:

add_options_page(
    'Theme Options',
    'Theme Options',
    'administrator',
    __FILE__, 
    array('KD_Options'),
    'display_options_page'
); 

Because you are within a Class, the callback needs to be array( $this, 'display_options_page' ) and not just a function name. You use that array format for WP callbacks within classes so that they are correctly referenced.

However, add_options_page takes 5 parameters, not 6, and they should be:

add_options_page(
    $page_title, 
    $menu_title, 
    $capability, 
    $menu_slug, 
    $function
);

So something like this should work:

add_options_page(
    'Theme Options',
    'Theme Options',
    'administrator',
    'wpse_233388_slug',
    array( $this, 'display_options_page' )
); 

You might be better off using a real capability rather than a role name for your capability too. That way other roles can be allowed the capability without making the users concerned administrators.