给你，解释作为评论

// setup array to store things in while we loop
$events_out = array();

// assume you already have your loop built the way you want
while($loop->have_posts()) : $loop->the_post();
    $instances = array();
    // grab meta dates
    $instances[] = get_post_meta($post->ID, \'dateA\', true);
    $instances[] = get_post_meta($post->ID, \'dateB\', true);
    $instances[] = get_post_meta($post->ID, \'dateC\', true);

    foreach($instances as $instance){
        if(!empty($instance)){
            // save into outter array with post_id so we can ref more data
            $events_out[] = array(
                \'timestamp\' => $instance,
                \'post_id\' => $post->ID,
            );
        }
    }

endwhile;

// use array_msort to sort by date! defined below
$events_sorted = array_msort($events_out, array(\'timestamp\' => SORT_ASC));

// output in order, with whatever meta/stuff you want
foreach($events_sorted as $event){
    echo \'<div>\';
    echo \'<h2>\'.get_the_title($event[\'post_id\']).\'</h2>\';
    echo \'<h3>\'.date(\'m/d/Y\', $event[\'timestamp\']).\'</h3>\';
    echo get_post_meta($event[\'post_id\'], \'some_meta_stuff\', true);
    echo \'<a href="\'.get_permalink($event[\'post_id\']).\'">Read More</a>\';
    echo \'</div>\';
}

/**
 * array_msort: array_multisort variant
 * use: array_msort($array, array(\'name\'=>SORT_DESC, \'cat\'=>SORT_ASC));
 */
function array_msort($array, $cols)
{
    $colarr = array();
    foreach ($cols as $col => $order) {
        $colarr[$col] = array();
        foreach ($array as $k => $row) { $colarr[$col][\'_\'.$k] = strtolower($row[$col]); }
    }
    $eval = \'array_multisort(\';
    foreach ($cols as $col => $order) {
        $eval .= \'$colarr[\\\'\'.$col.\'\\\'],\'.$order.\',\';
    }
    $eval = substr($eval,0,-1).\');\';
    eval($eval);
    $ret = array();
    foreach ($colarr as $col => $arr) {
        foreach ($arr as $k => $v) {
            $k = substr($k,1);
            if (!isset($ret[$k])) $ret[$k] = $array[$k];
            $ret[$k][$col] = $array[$k][$col];
        }
    }
    return $ret;
}