I'm using the example from add_image_size() | WordPress Developer Resources to try to add custom image sizes to the admin media selector.

add_filter( 'image_size_names_choose', 'my_custom_sizes' );

function my_custom_sizes( $sizes ) {
    return array_merge( $sizes, array(
        'your-custom-size' => __( 'Your Custom Size Name' ),
    ) );
}

But I'm getting a PHP Warning:

call_user_func_array() expects parameter 1 to be a valid callback, function 'my_custom_sizes' not found or invalid function name

and the media size selector is empty:

The answers to Adding custom image size to the media image editor and add_image_size and add_filter('image_size_names_choose', 'my_custom_image_sizes') not working with wordpress 3.5.2 don't work.

I'm using the filter and add_image_size inside after_setup_theme; see below. I've tried it outside with no luck. Thumbnails are being generated, and regenerating thumbs works, too.

What is breaking?

function setup()
{

// other code


add_image_size( 'banner-ad', 655, 100, true );
add_image_size( 'banner-rectangle', 655, 250, true );


add_filter( 'image_size_names_choose', 'my_custom_sizes' );

function my_custom_sizes( $sizes ) {
    return array_merge( $sizes, array(
        'banner-ad' => __( 'Banner Ad' ),
        'banner-rectangle' => __( 'Banner Rectangle' ),
    ) );
}



// other code
}
add_action('after_setup_theme', __NAMESPACE__ . '\\setup');

I'm using the example from add_image_size() | WordPress Developer Resources to try to add custom image sizes to the admin media selector.

add_filter( 'image_size_names_choose', 'my_custom_sizes' );

function my_custom_sizes( $sizes ) {
    return array_merge( $sizes, array(
        'your-custom-size' => __( 'Your Custom Size Name' ),
    ) );
}

But I'm getting a PHP Warning:

call_user_func_array() expects parameter 1 to be a valid callback, function 'my_custom_sizes' not found or invalid function name

and the media size selector is empty:

The answers to Adding custom image size to the media image editor and add_image_size and add_filter('image_size_names_choose', 'my_custom_image_sizes') not working with wordpress 3.5.2 don't work.

I'm using the filter and add_image_size inside after_setup_theme; see below. I've tried it outside with no luck. Thumbnails are being generated, and regenerating thumbs works, too.

What is breaking?

function setup()
{

// other code


add_image_size( 'banner-ad', 655, 100, true );
add_image_size( 'banner-rectangle', 655, 250, true );


add_filter( 'image_size_names_choose', 'my_custom_sizes' );

function my_custom_sizes( $sizes ) {
    return array_merge( $sizes, array(
        'banner-ad' => __( 'Banner Ad' ),
        'banner-rectangle' => __( 'Banner Rectangle' ),
    ) );
}



// other code
}
add_action('after_setup_theme', __NAMESPACE__ . '\\setup');

• php
• functions
• actions

• It might just be the copy/paste but I think you're missing a } after the function. Assuming that it's supposed to be insde the setup() function. – Welcher Commented May 1, 2019 at 17:12
• Thanks, that was missing; but that would cause a fatal error, too. – BlueDogRanch Commented May 1, 2019 at 17:16

3 Answers 3

You can't define a hook callback function inside another function.

You've defined my_custom_sizes() inside setup(), which means that my_custom_sizes() cannot be called outside of the scope of setup(). This is a problem because the hook, image_size_names_choose, is not run inside your setup() function. You need to define your callback in the global scope:

function setup()
{
    add_image_size( 'banner-ad', 655, 100, true );
    add_image_size( 'banner-rectangle', 655, 250, true );

}
add_action('after_setup_theme', __NAMESPACE__ . '\\setup');

function my_custom_sizes( $sizes )
{
    return array_merge( $sizes, array(
        'banner-ad' => __( 'Banner Ad' ),
        'banner-rectangle' => __( 'Banner Rectangle' ),
    ) );
}
add_filter( 'image_size_names_choose', __NAMESPACE__ . '\\my_custom_sizes' );

Try defining the my_custom_sizes() function outside of the setup() function.

I'm pretty sure that the my_custom_sizes() function is only available in the scope of the setup() function - which has already been called before the image_size_names_choose filter is fired and so it's not available to it.

Try this

function my_custom_sizes( $sizes ) {
    return array_merge( $sizes, array(
        'banner-ad' => __( 'Banner Ad' ),
        'banner-rectangle' => __( 'Banner Rectangle' ),
    ) );
}
add_filter( 'image_size_names_choose', 'my_custom_sizes' );


function setup()
{

// other code


add_image_size( 'banner-ad', 655, 100, true );
add_image_size( 'banner-rectangle', 655, 250, true );



// other code
}
add_action('after_setup_theme', __NAMESPACE__ . '\\setup');