如果我理解正确的话，您正在输入代码header.php, 文件中需要的single-dress.php 使用get_header(), 在同一个文件中，在大约20多行之后，定义在20多行之前使用的变量。

因此，要么您的服务器有嵌入式时间机器，要么您的代码无法工作。

你要做的就是在使用变量之前定义它们。

也许，与其把代码弄乱，不如用一系列if / elseif, 您可以将逻辑与模板分离。

我将编写一个简单的类来处理预取。您可以将其保存在单独的文件中，并从functions.php.

请阅读内联注释以获取更多解释。

<?php
class My_Theme_Prefetcher {

    public $next_url;
    public $prev_url;

    function setup() {
        global $wp_query;
        // for empty query there is nothing to prefetch 
        if ( ! $wp_query instanceof WP_Query || $wp_query->found_posts <= 0  ) return;
        if ( $wp_query->is_archive() ) {
            // next page URL for archives, that is empty if there is no next page URL
            $this->next_url = get_next_posts_page_link();
        } elseif ( $wp_query->is_singular( \'dress\' ) ) {
            // if on a single page view for dress CPT, run a query for dress posts
            $this->set_dress_query( $wp_query->get_queried_object_id() );
        }
        // A filter to easily get class instance and access to instance methods and vars
        add_filter( \'my_theme_prefetcher\', function() { return $this; } );
        // output the prefetch strings on wp_head
        add_action( \'wp_head\', array( $this, \'output\' ) );
    }

    /**
    * Perform a query to get all dresses in same collection,
    * save adjacent post URLs into instance properties
    */
    function set_dress_query( $dressid ) {
        $args =  static::dress_query_args( $dressid );
        if ( empty( $args ) ) return;
        $dress_query = new WP_Query( $args );
        if ( $dress_query->found_posts > 0 ) {
            // some dresses found, discover and save adjacent URLs
            $adjacents = static::get_adjacents( $dressid, $dress_query->posts );
            if ( $adjacents[\'next\'] ) 
                $this->next_url = get_permalink( $adjacents[\'next\'] );
            if ( $adjacents[\'prev\'] ) 
                $this->prev_url = get_permalink( $adjacents[\'prev\'] );
        }
    }

    /**
    * Given a current ID and a set of posts, discover adjacent posts
    */
    static function get_adjacents( $current, Array $all ) {
        $adjacents = array( \'prev\' => FALSE, \'next\' => FALSE );
        if ( is_numeric( $current ) && ! empty( $all ) ) {
            $ids = wp_list_pluck( $all, \'ID\' );
            $this_posts = array_search( $current, $ids );
            if ( $this_posts !== FALSE ) {
                $prev_i = $this_posts > 0 ? $this_posts -1 : FALSE;
                $next_i = $this_posts < count( $ids ) - 1 ? $this_posts + 1 : FALSE;
                $previous = $prev_i !== FALSE ? $all[ $prev_i ] : FALSE;
                $next = $next_i !== FALSE ? $all[ $next_i ] : FALSE;
                $adjacents = array( \'prev\' => $previous, \'next\' => $next );
            }
        }
        return $adjacents;
    }

    /**
    * Output prefetch string on wp_head. Do nothing if no, or invalid, URL is set
    */
    function output() {
        if (
            empty( $this->next_url ) ||
            ! filter_var( $this->next_url, FILTER_VALIDATE_URL )
        ) return;
        $format = \'<link rel="prefetch" href="%1$s"><link rel="prerender" href="%1$s">\';
        printf( $format, esc_url( $this->next_url ) );
    }

    /**
    * Returns the args for dress query for a given dress id.
    */
    static function dress_query_args( $dressid ) {
        $collections = get_the_terms( $dressid, \'collections\' );
        if ( is_wp_error( $collections ) || empty( $collections ) ) return;
        $term = array_shift( $collections );
        $args = array(
            \'post_type\' => \'dress\',
            \'posts_per_page\' => -1,
            \'tax_query\' => array(
                array( \'taxonomy\' => \'collections\', \'terms\' => array( $term->term_id ) )
            ),
            \'order\' => \'ASC\',
            \'orderby\' => \'title\'
        );
        return $args;
    }

}

所有逻辑都在类中：当setup() 方法时，类将查看当前查询，如果它是存档，则设置指向下一个存档页的下一个URL。如果该页面用于单个连衣裙视图，则会运行查询以获取同一集合中的所有连衣裙，如果找到，则将相邻的帖子URL保存在实例变量中。

现在我们需要启动该类，即调用setup() 钩子上的方法在设置主查询后激发，但在设置前激发wp_head() 被称为：\'template_include\' 将是完美的。

我不使用template_redirect 此处允许在需要时进行更快的重定向（无需触发其他查询）。然而\'template_include\' 是一个筛选器，因此我们必须返回当前模板。添加到您的functions.php:

add_filter( \'template_include\', function( $template ) {
    $prefetcher = new My_Theme_Prefetcher;
    $prefetcher->setup();
    return $template;
} );

现在，你只需要确定header.php 这里有wp_head() 类将添加调用和预回迁链接。

还有另一项任务要做。在模板文件中(single-dress.php) 我们需要显示相邻帖子链接，但不需要运行另一个查询，因为相邻帖子URL已经保存在My_Theme_Prefetcher 在上实例化\'template_include\'.

因此，我们需要访问该实例和自定义筛选器\'my_theme_prefetcher\' 为作用域创建的。

因此，在模板中，您可以：

<figure class="pinboard">
    <?php

    // here goes your thumbnail image stuff, I will not copy it...

    // get the prefetcher instance and check it
    $prefetcher = apply_filters( \'my_theme_prefetcher\', NULL );

    if ( $prefetcher instanceof My_Theme_Prefetcher ) { 
        // we got prefetcher instance, get the urls
        $prev_url = $prefetcher->prev_url ? : FALSE;
        $next_url = $prefetcher->next_url ? : FALSE;
    } else {
        // something goes wrong, try to run the query
        // function that returns arguments is static, so we can access it
        $args = My_Theme_Prefetcher::dress_query_args( $post->ID );
        $dress_by_tax = ! empty( $args ) ? new WP_Query( $args ) : FALSE;
        if ( $dress_by_tax instanceof WP_Query && ! empty( $dress_by_tax->posts ) ) {
            // function that returns adjacent posts is static, so we can access it
            $adjacents = My_Theme_Prefetcher::get_adjacents( $post->ID, $dress_by_tax->posts );
            $next_url = $adjacents[\'next\'] ? get_permalink( $adjacents[\'next\'] ) : FALSE;
            $prev_url = $adjacents[\'prev\'] ? get_permalink( $adjacents[\'prev\'] ) : FALSE;
        } else {
            $next_url = $prev_url = FALSE;
        }
    }
    ?>

    <?php if ( $next_url ) : ?>
        <div class="nav-next arrow block button spaced ribbon">
            <a href="<?php echo $next_url ?>">Next</a>
        </div>
    <?php endif; ?>

    <?php if ( $prev_url ) : ?>
        <div class="nav-prev arrow-left block button spaced ribbon2 left">
            <a href="<?php echo $prev_url ?>">Previous</a>
        </div>
    <?php endif; ?>

    <div class="mask"><span>Click for larger size</span></div>

</figure>