John Davidson

Message:

I am trying to add a new category for some custom blocks using the block_categories_all filter.

I am using TwentyTwentyOne theme and putting the code below into the functions.php file. No plugins at all are installed.

When I dump $new_cats the array_merge has been successful but throws header already sent warning.

function wpdocs_add_new_block_category( $block_categories ) {

 

    $new_cats = array_merge(

        $block_categories,

        [

            [

                'slug'  => 'my-block-category',

                'title' => esc_html__( 'My Block Category', 'text-domain' ),

                'icon'  => 'wordpress', // Slug of a WordPress Dashicon or custom SVG

            ],

        ]

    );

    

    # var_dump($new_cats);



    return ($new_cats);

}

 

add_filter( 'block_categories_all', 'wpdocs_add_new_block_category', 10, 2 );

There must be something simple I am missing here??

---

My Answer:
> To avoid the "header already sent" warning, you should make sure that there is no whitespace or any other output before the `
Here is the corrected code for adding a new block category:

php
function wpdocs_add_new_block_category( $block_categories ) {
$new_cats = array_merge(
$block_categories,
[
[
'slug' => 'custom-blocks',
'title' => 'Custom Blocks',
],
]
);

return $new_cats;
}
add_filter( 'block_categories_all', 'wpdocs_add_new_block_category' );


Make sure to place this code at the end of your functions.php file, after any closing PHP tags `?>` to avoid any whitespace issues. This should add a new category called "Custom Blocks" to the block editor in WordPress.