However, this will turn ALL terms checkboxes to radio buttons.
Not only that, it’ll turn any checkbox in a meta box – not ideal!
Instead, let’s specifically target the wp_terms_checklist() function, which is used to generate the list of checkboxes across the admin (including quick edit).
/**
* Use radio inputs instead of checkboxes for term checklists in specified taxonomies.
*
* @param array $args
* @return array
*/
function wpse_139269_term_radio_checklist( $args ) {
if ( ! empty( $args['taxonomy'] ) && $args['taxonomy'] === 'category' /* <== Change to your required taxonomy */ ) {
if ( empty( $args['walker'] ) || is_a( $args['walker'], 'Walker' ) ) { // Don't override 3rd party walkers.
if ( ! class_exists( 'WPSE_139269_Walker_Category_Radio_Checklist' ) ) {
/**
* Custom walker for switching checkbox inputs to radio.
*
* @see Walker_Category_Checklist
*/
class WPSE_139269_Walker_Category_Radio_Checklist extends Walker_Category_Checklist {
function walk( $elements, $max_depth, ...$args ) {
$output = parent::walk( $elements, $max_depth, ...$args );
$output = str_replace(
array( 'type="checkbox"', "type="checkbox"" ),
array( 'type="radio"', "type="radio"" ),
$output
);
return $output;
}
}
}
$args['walker'] = new WPSE_139269_Walker_Category_Radio_Checklist;
}
}
return $args;
}
add_filter( 'wp_terms_checklist_args', 'wpse_139269_term_radio_checklist' );
We hook onto the wp_terms_checklist_args filter, then implement our own custom “walker” (a family of classes used to generate hierarchical lists). From there, it’s a simply string replace of type="checkbox" with type="radio" if the taxonomy is whatever we’ve configured it to match (in this case “category”).