Adding CSS to custom post type admin page causes error

Question

I have this bit of code in my Meteor Slides plugin that loads a stylesheet on the admin pages of just the slides custom post type:

    add_action('admin_head', 'meteorslides_admin_css');

function meteorslides_admin_css() {

    global $post_type;

    if (($_GET['post_type'] == 'slide') || ($post_type == 'slide')) :

        echo "<link type='text/css' rel='stylesheet' href='" . plugins_url('/css/meteor-slides-admin.css', __FILE__) . "' />";

    endif;

}

This code works fine and hasn't cause any issues, but in debug mode, it does cause this error that I'd like to resolve:

// Notice: Undefined index: post_type in C:\Program Files\xampp\htdocs\slides\wp-content\plugins\meteor-slides-1.3\meteor-slides-plugin.php on line 476

I haven't been able to fix this error, does anyone have any suggestions, or a different way to add a stylesheet to the admin pages of a certain post type?

Answer 1

You need to check for the presence of 'post_type' as an index of $_GET before using it:

if ((isset($_GET['post_type']) && $_GET['post_type'] == 'slide') || (isset($post_type) && $post_type == 'slide')) :

Also, you should be using the wp_enqueue_style function instead of echoing your stylesheet at 'admin_head':

wp_enqueue_style( 'meteor-slides-admin', plugins_url('/css/meteor-slides-admin.css', __FILE__), array(), '1.0' );

More information on wp_enqueue_style here.

Answer 2

There are hooks for adding actions to specific pages.. and additionally various variables that hold data about the current page, the post type, the parent file, etc..

admin_print_styles would be the correct hook to use for enqueuing styles, and for the edit page your action could look a little something like this..

add_action( 'admin_print_styles-edit.php', 'example_function' ); // Will work for any post type, check inside the callback function
//add_action( 'admin_print_styles-post-new.php', 'example_function' ); // Example
//add_action( 'admin_print_styles-edit-tags.php', 'example_function' ); // Example
function example_function() {
    global $typenow;
    if( 'my_custom_type' == $typenow )
        wp_enqueue_style( 'meteor-slides-admin', plugins_url('/css/meteor-slides-admin.css'), array(), '1.0' );
}

In this case the hook is edit.php, each admin page has a similar hook. WordPress admin_header.php basically has a set of actions that fire, which look like so..

do_action('admin_enqueue_scripts', $hook_suffix);
do_action("admin_print_styles-$hook_suffix");
do_action('admin_print_styles');
do_action("admin_print_scripts-$hook_suffix");
do_action('admin_print_scripts');
do_action("admin_head-$hook_suffix");
do_action('admin_head');

And admin.php sets the hook suffix with the following..

$hook_suffix = '';
if ( isset($page_hook) )
    $hook_suffix = $page_hook;
else if ( isset($plugin_page) )
    $hook_suffix = $plugin_page;
else if ( isset($pagenow) )
    $hook_suffix = $pagenow;

All the core code aside, the example function i posted further up is a working example you can use for targetting the edit posts(custom type or not) screen....

Hope that helps..