如果日期是字符串，如何按日期排序？

Question

我为具有自定义字段且带有诸如22/5/2018这样的字符串的帖子运行循环，我需要按日期对帖子进行排序，所以我这样做：

$postOrdered = array();
$queryPosts = new WP_Query(array(
    'posts_per_page' => -1,
    'post__in' => $postIds,
    'order'   => 'DESC',
    'orderby'   => 'DATE',
    'meta_key'  => 'usp-custom-80',
    'type' => 'DATE',
    )
);

if( $queryPosts->have_posts() ):
    while ( $queryPosts->have_posts() ) : $queryPosts->the_post();
        array_push($postOrdered, $post->ID);
        $date = usp_get_meta(false, 'usp-custom-80');
        echo $date."<br>";
    endwhile;
endif;

我得到：

2-6-2015
21-12-2018
26-12-2018
18-12-2018
27-12-2018
12-11-2018
21-12-2018
7-12-2018
5-12-2018
5-12-2018
6-12-2018
19-12-2018
7-12-2018
13-12-2018
24-11-2000
25-11-2018
13-11-2018

我想通过这样做将字符串转换为日期

$postOrdered = array();
$date = usp_get_meta(false, 'usp-custom-80');
$date = DateTime::createFromFormat("d.m.Y", $date)->format("m/d/Y");
$queryPosts = new WP_Query(array(
    'posts_per_page' => -1,
    'post__in' => $postIds,
    'order'   => 'DESC',
    'orderby'   => $date,
    'meta_key'  => 'usp-custom-80',
    'type' => 'DATE',
    )
);

if( $queryPosts->have_posts() ):
    while ( $queryPosts->have_posts() ) : $queryPosts->the_post();
        array_push($postOrdered, $post->ID);
        $dateOrdered =  usp_get_meta(false, 'usp-custom-80');
        echo $dateOrdered."<br>";
    endwhile;
endif;

但是我什么也没得到

Answer 1

将代码更改为如下所示：

if( $queryPosts->have_posts() ):
    $dateOrdered = [];
    while ( $queryPosts->have_posts() ) : $queryPosts->the_post();
        array_push($postOrdered, $post->ID);
        $dateOrdered[] =  usp_get_meta(false, 'usp-custom-80');
        //echo $dateOrdered."<br>";
    endwhile;
endif;

function custom_sort_dt($a, $b) {
    return strtotime($a) - strtotime($b);
}
usort($dateOrdered, "custom_sort_dt");
print_r($dateOrdered);

请参考：

Post