How to make a image-size selected by default in Media upload – WP v3.5

Bare with me. I want to have a custom image size selected by default in the Media upload popup page. In WordPress v3.4.2 and prior, this elegant code worked fine:

function my_insert_custom_image_sizes( $sizes ) {
    // get the custom image sizes
    global $_wp_additional_image_sizes;
    // if there are none, just return the built-in sizes
    if ( empty( $_wp_additional_image_sizes ) )
        return $sizes;

    // add all the custom sizes to the built-in sizes
    foreach ( $_wp_additional_image_sizes as $id => $data ) {
        // take the size ID (e.g., 'my-name'), replace hyphens with spaces,
        // and capitalise the first letter of each word
        if ( !isset($sizes[$id]) )
            $sizes[$id] = ucfirst( str_replace( '-', ' ', $id ) );
    }

    return $sizes;
}


// Which custom image size selected by default
function my_set_default_image_size () { 
     return 'custom-image-size-2';
}


function custom_image_setup () {
    add_theme_support( 'post-thumbnails' );
    add_image_size( 'custom-image-size-1', 160, 9999 ); //  columned
    add_image_size( 'custom-image-size-2', 300, 9999 ); //  medium
    add_image_size( 'custom-image-size-3', 578, 190, true ); //  cropped
    add_filter( 'image_size_names_choose', 'my_insert_custom_image_sizes' );
    add_filter( 'pre_option_image_default_size', 'my_set_default_image_size' );
}

add_action( 'after_setup_theme', 'custom_image_setup' );

So, my_insert_custom_image_sizes adds the custom images to the media page and my_set_default_image_size should select the custom-image-size-2 size. This code stopped working with the WordPress 3.5 version. Do you know how I can accomplish this in v3.5?

Try this out. Your add_filter()’s second argument is a function, that will affect the current option via a return:

function theme_default_image_size() {
    return 'custom-image-size-2';
}
add_filter( 'pre_option_image_default_size', 'theme_default_image_size' );

You could also look into the pre_update_option_{$option} filter, and update the value once, so you don’t need to run this filter every time (may save 0.01s, but it’s still saving!) 🙂

or good old update_option():

update_option( 'image_default_size', 'custom-image-size-2' );