Advanced custom fieldを使用

releases.php

<div class="releases_list">
		<?php
		$paged = ( get_query_var( 'paged' ) ) ? get_query_var( 'paged' ) : 1;
		$query = new WP_Query(array(
			'posts_per_page' => 4,
			'post_type' => 'releases',
			'orderby' => 'date',
			'paged' => $paged
		)); ?>
		<?php $prev_year = null; ?>
		<?php if ($query -> have_posts()): ?><?php while ($query -> have_posts()) : $query -> the_post(); ?> 
			<?php $this_year = get_the_date('Y'); ?>
			<?php if ($prev_year != $this_year):  ?>
					<div class="releases_list_year"><p><?php echo $this_year; ?></p></div>
			<?php endif; ?>
			<ul class="releases_list_news">
				<li class="releases_list_news_list">
					<dl class="releases_list_news_dl">
						<dt class="releases_list_news_ttl"><p><?php the_time('Y-n-j'); ?></p></dt>
						<dd class="releases_list_news_read">
							<a><?php the_field('news'); ?></a>
						</dd>
					</dl>
				</li>
			</ul>
		<?php $prev_year = $this_year; ?>
		<?php endwhile; ?><?php endif; ?>
	</div>		
	<div class="pagi">
		<?php custom_pagination('/releases/', $paged, $query->max_num_pages); ?>
	</div>

参考サイト:
https://stackoverflow.com/questions/3397725/wordpress-how-can-i-display-post-link-group-by-year

functions.php

function custom_pagination($uri, $current, $last, $range = 5){
    $showitems = ($range * 2)+1;
    if(preg_match('/\\?/', $uri)){
        $uri .= '&';
    } else {
        $uri .= '?';
    }
    if(1 !== (int)$last){
        $prev = $current-1;
        $next = $current+1;
        $currentPage = false;
        $beforePage = false;
        $afterNum = 0;
        $path = get_template_directory_uri();
        echo "<div class='page_nsv'>";
        // echo  "<p class=\"prev prne nav_list\"><a href=\"{$uri}paged={$prev}\">&lt;</a></p>";
		echo  "<ul class=\"nav_list nav_con_list dot_left dot_right\">";
        for ($i=1; $i <= $last; $i++){
            if($i === 1 && $current !== 1){
                 echo "<p class=\"prev prne nav_list\"><a href=\"{$uri}paged={$prev}\">&lt;</a></p>";
            }
            if($current === $i){
                echo "<li class=\"nav_con_list_li\"><a href=\"#\" onclick=\"return false;\" class=\"page-link\">{$current}</a></li>";
            } else {
                echo "<li class=\"nav_con_list_li\"><a href=\"{$uri}paged={$i}\" class=\"page-link\">{$i}</a></li>";
            }
            if($i == $last && $current != $last){
                 echo "<li class=\"nav_con_list_li\"><a class=\"page-link\" href=\"{$uri}paged={$next}\"></a></li><p class=\"next prne nav_list\"></p>";
                 echo "<p class=\"next prne nav_list\"><a href=\"{$uri}paged={$next}\">&gt;</a></p>";
            }
        }
        echo "</ul>";
        echo "<p class=\"next prne nav_list\"></p>";
        echo "</div>";  
    }
}

functions.phpでページネーションを設定

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