管理画面、投稿一覧の既存のカラムに表示項目を追加 | WordPressのカスタマイズ

<?php
    if ( 'excerpt' === $mode ) {
        /**
            * Filters the published time of the post.
            *
            * If `$mode` equals 'excerpt', the published time and date are both displayed.
            * If `$mode` equals 'list' (default), the publish date is displayed, with the
            * time and date together available as an abbreviation definition.
            *
            * @since 2.5.1
            *
            * @param string  $t_time      The published time.
            * @param WP_Post $post        Post object.
            * @param string  $column_name The column name.
            * @param string  $mode        The list display mode ('excerpt' or 'list').
            */
        echo apply_filters( 'post_date_column_time', $t_time, $post, 'date', $mode );
    } else {

        /** This filter is documented in wp-admin/includes/class-wp-posts-list-table.php */
        echo '<span title="' . $t_time . '">' . apply_filters( 'post_date_column_time', $h_time, $post, 'date', $mode ) . '</span>';
    }
?>

<?php
    function add_modified_date_column( $h_time, $post, $column_name, $mode  ) {
        if ( 'diys' === $post->post_type ) {
            if ( 'list' === $mode ) {
                $modified = date( 'Y/m/d', strtotime( $post->post_modified ) );
                $h_time .= '<br>更新日:' . $modified;
            }
        }
        return $h_time;
    }
    add_filter('post_date_column_time','add_modified_date_column', 10, 4 );
?>