子カテゴリを非表示に

default-widgets.phpの533行目当たりから始まる部分が
カテゴリ一覧ウィジェットを生成する部分みたいです。


/**
 * Categories widget class
 *
 * @since 2.8.0
 */
class WP_Widget_Categories extends WP_Widget {

	public function __construct() {
		$widget_ops = array('classname' => 'widget_categories', 'description' => __( "A list or dropdown of categories." ) );
		parent::__construct('categories', __('Categories'), $widget_ops);
	}

	public function widget( $args, $instance ) {

		/** This filter is documented in wp-includes/default-widgets.php */
		$title = apply_filters( 'widget_title', empty( $instance['title'] ) ? __( 'Categories' ) : $instance['title'], $instance, $this->id_base );

		$c = ! empty( $instance['count'] ) ? '1' : '0';
		$h = ! empty( $instance['hierarchical'] ) ? '1' : '0';
		$d = ! empty( $instance['dropdown'] ) ? '1' : '0';

		echo $args['before_widget'];
		if ( $title ) {
			echo $args['before_title'] . $title . $args['after_title'];
		}

		$cat_args = array( 'orderby' => 'name', 'show_count' => $c, 'hierarchical' => $h);

		if ( $d ) {
			$cat_args['show_option_none'] = __('Select Category');

			/**
			 * Filter the arguments for the Categories widget drop-down.
			 *
			 * @since 2.8.0
			 *
			 * @see wp_dropdown_categories()
			 *
			 * @param array $cat_args An array of Categories widget drop-down arguments.
			 */
			wp_dropdown_categories( apply_filters( 'widget_categories_dropdown_args', $cat_args ) );
?>

<script type='text/javascript'>
/* <![CDATA[ */
	var dropdown = document.getElementById("cat");
	function onCatChange() {
		if ( dropdown.options[dropdown.selectedIndex].value > 0 ) {
			location.href = "<?php echo home_url(); ?>/?cat="+dropdown.options[dropdown.selectedIndex].value;
		}
	}
	dropdown.onchange = onCatChange;
/* ]]> */
</script>

<?php
		} else {
?>
		<div id="right_categories">
		<ul>
<?php
		$cat_args['title_li'] = '';

		/**
		 * Filter the arguments for the Categories widget.
		 *
		 * @since 2.8.0
		 *
		 * @param array $cat_args An array of Categories widget options.
		 */
		wp_list_categories( apply_filters( 'widget_categories_args', $cat_args ) );
?>
		</ul>
		</div>
<?php
		}

		echo $args['after_widget'];
	}

	public function update( $new_instance, $old_instance ) {
		$instance = $old_instance;
		$instance['title'] = strip_tags($new_instance['title']);
		$instance['count'] = !empty($new_instance['count']) ? 1 : 0;
		$instance['hierarchical'] = !empty($new_instance['hierarchical']) ? 1 : 0;
		$instance['dropdown'] = !empty($new_instance['dropdown']) ? 1 : 0;

		return $instance;
	}

	public function form( $instance ) {
		//Defaults
		$instance = wp_parse_args( (array) $instance, array( 'title' => '') );
		$title = esc_attr( $instance['title'] );
		$count = isset($instance['count']) ? (bool) $instance['count'] :false;
		$hierarchical = isset( $instance['hierarchical'] ) ? (bool) $instance['hierarchical'] : false;
		$dropdown = isset( $instance['dropdown'] ) ? (bool) $instance['dropdown'] : false;
?>
		<p><label for="<?php echo $this->get_field_id('title'); ?>"><?php _e( 'Title:' ); ?></label>
		<input class="widefat" id="<?php echo $this->get_field_id('title'); ?>" name="<?php echo $this->get_field_name('title'); ?>" type="text" value="<?php echo $title; ?>" /></p>

		<p><input type="checkbox" class="checkbox" id="<?php echo $this->get_field_id('dropdown'); ?>" name="<?php echo $this->get_field_name('dropdown'); ?>"<?php checked( $dropdown ); ?> />
		<label for="<?php echo $this->get_field_id('dropdown'); ?>"><?php _e( 'Display as dropdown' ); ?></label><br />

		<input type="checkbox" class="checkbox" id="<?php echo $this->get_field_id('count'); ?>" name="<?php echo $this->get_field_name('count'); ?>"<?php checked( $count ); ?> />
		<label for="<?php echo $this->get_field_id('count'); ?>"><?php _e( 'Show post counts' ); ?></label><br />

		<input type="checkbox" class="checkbox" id="<?php echo $this->get_field_id('hierarchical'); ?>" name="<?php echo $this->get_field_name('hierarchical'); ?>"<?php checked( $hierarchical ); ?> />
		<label for="<?php echo $this->get_field_id('hierarchical'); ?>"><?php _e( 'Show hierarchy' ); ?></label></p>
<?php
	}

}


559行目からの部分がカテゴリ一覧を抽出する部分の様で、ここに depth という引数を記入します。 depth => 1 が’第一階層のみを表示’のようです。なので

$cat_args = array('depth' => '1', 'orderby' => 'name', 'show_count' => $c, 'hierarchical' => $h);

で親カテゴリだけが表示されます。