Creates an HTML dropdown (<option> elements) for categories.

Since: 2.1.0
Source: wp-includes/class-walker-category-dropdown.php
Used by: wp_dropdown_categories()

Class Synopsis

class Walker_CategoryDropdown extends Walker {
    public $tree_type = 'category';
    public $db_fields = [
        'parent' => 'parent',
        'id'     => 'term_id',
    ];
    
    public function start_el( &$output, $data_object, $depth = 0, $args = [], $current_object_id = 0 );
}

Configuration

$db_fields

public $db_fields = [
    'parent' => 'parent',    // WP_Term->parent
    'id'     => 'term_id',   // WP_Term->term_id
];

Methods

start_el()

Outputs a single <option> element for a category.

public function start_el( &$output, $data_object, $depth = 0, $args = [], $current_object_id = 0 )

Args used:

• selected — Value to mark as selected
• show_count — Append post count
• value_field — Term field to use for option value (default: 'term_id')

Output:

<option class="level-0" value="5">News</option>
<option class="level-1" value="8">&nbsp;&nbsp;&nbsp;Local News</option>
<option class="level-1" value="9" selected="selected">&nbsp;&nbsp;&nbsp;World News&nbsp;&nbsp;(42)</option>

No List Methods

This walker only implements start_el(). Dropdowns don’t need:

• start_lvl() / end_lvl() — No container elements between levels
• end_el() — <option> is self-closing in the context

Depth Indication

Hierarchy is shown through   padding:

• Depth 0: No padding
• Depth 1: 3   characters
• Depth 2: 6   characters
• Depth n: n * 3   characters

Usage Example

// Direct usage
$walker = new Walker_CategoryDropdown();
$categories = get_terms( [
    'taxonomy'   => 'category',
    'hide_empty' => false,
] );

echo '<select name="cat">';
echo '<option value="">Select Category</option>';
echo $walker->walk( $categories, 0, [
    'selected'    => get_query_var( 'cat' ),
    'show_count'  => true,
    'value_field' => 'slug',  // Use slug instead of term_id
] );
echo '</select>';

// Via wp_dropdown_categories()
wp_dropdown_categories( [
    'show_option_none' => 'Select Category',
    'selected'         => $current_cat,
    'hierarchical'     => true,
    'value_field'      => 'term_id',
] );

Custom Value Field

The value_field argument lets you change what’s used for the option value:

// Use term slug
wp_dropdown_categories( [
    'value_field' => 'slug',
] );
// Output: <option value="news">News</option>

// Use term_id (default)
wp_dropdown_categories( [
    'value_field' => 'term_id',
] );
// Output: <option value="5">News</option>

Extending

class My_Category_Dropdown extends Walker_CategoryDropdown {
    public function start_el( &$output, $category, $depth = 0, $args = [], $current = 0 ) {
        $pad = str_repeat( '— ', $depth );  // Use dashes instead of spaces
        
        $output .= sprintf(
            '<option value="%s"%s>%s%s</option>',
            esc_attr( $category->term_id ),
            selected( $args['selected'], $category->term_id, false ),
            $pad,
            esc_html( $category->name )
        );
    }
}

Related

• wp_dropdown_categories() — Main function using this walker
• Walker_Category — List version
• list_cats filter — Modify category name