Dynamically changing navigation links (next and previous) in WordPress via AJAX

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Inside the loop of single.php, I have a select tag in which the options are the posts of the current category returned via a custom query.

On changing selected option, I have many javascript functions that are working well, but the last function among them (function f_next-previous), doesnt seem to work.

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The aim of this function is to update the next and previous links without reloading the page.

Here is the code for navigation links (next and previous) in template: 

<div id="nav-above" class="navigation">

<div class="nav-previous"><?php previous_post_link( '%link', '<img height="34" src="' . get_bloginfo("template_directory") . '/images/previous.png" />' ); ?></div>

<div class="nav-next"><?php next_post_link( '%link', '<img height="34" src="' . get_bloginfo("template_directory") . '/images/next.png" />' ); ?></div>

</div><!-- #nav-above -->

The javascript code of this function is: 

function f_next-previous(id)
{
       $.ajax({  
       cache: true,  
       type: "GET",  
       timeout: 5000,   
       url: 'wp-content/themes/twentyten/pages/next-previous.php?p='+id,  
       success: function(msg)  
        {  

    $('#nav-above').html(msg);

        },  
        error: function(msg)  
        {  
           alert("Your browser broke!");
                return false;
        }  
});

}

The file next-previous.php content is : 

<?php
$p=$_GET['p']; 
require( '../../../wp-load.php' );



$my_query = new WP_Query();
$my_query->query(array( 'post__in' => array($p)));

if ($my_query->have_posts()) : while ($my_query->have_posts()) : $my_query->the_post();  ?>


<div class="nav-previous"><?php previous_post_link( '%link', '<img height="34" src="' . get_bloginfo("template_directory") . '/images/previous.png" />' ); ?></div>
<div class="nav-next"><?php next_post_link( '%link', '<img height="34" src="' . get_bloginfo("template_directory") . '/images/next.png" />' ); ?></div>

<?php

endwhile;
endif;

?>

While testing this php file by giving it a value to the p parameter, it gives logical result in the browser. Jquery and function scripts are well included and all AJAX in my website is ok. What am I missing in this work????

UPDATE:
Note that the part of my single.php file responsible of triggering the AJAX call is: 

   <form method="post" action="">  

    <select class="select2"  name="" id="" >
    <option value="<?php the_ID();?>"><?php the_title();?></option>

    <?php 
global $post;
$paged = get_query_var( 'paged' ) ? get_query_var( 'paged' ) : 1;
$myposts = get_posts("paged=$paged&category=4");

foreach($myposts as $post) :?>

        <option value="<?php the_ID();?>"><?php the_title();?></option>

        <?php endforeach;
        wp_reset_postdata(); ?> 

        </select>
        </form>
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1 comment

  1. First, I want to note that the approach I mentionned in my question is bad according to almost tutorials talking about AJAX in wordpress. So I decided to change it based on the advice of hakre and his link : http://codex.wordpress.org/AJAX_in_Plugins#Ajax_on_the_Viewer-Facing_Side.

    In other words, the best way for my situation is to use the built-in AJAX in WordPress, using the wp-admin/admin-ajax.php. AJAX requests should be directed to this file. I know the “admin” part of the file name is a bit misleading. but all requests in the front-end (the viewing side) as well as the admin panel can be processed in admin-ajax.php, with a lot of benefits, especially for security.

    The steps are:

    1.The JavaScript code that submits the AJAX request should look something like this:

        $(document).ready(function() {
        $('.select2').change(function(e) {
    e.preventDefault();

    var v = $('.select2 option:selected').val(); 


            $.ajax({
                type: "GET",
                url: "wp-admin/admin-ajax.php", // check the exact URL for your situation
                dataType: 'html',
                data: ({ action: 'nextPrevious', id: v}),
                success: function(data){

                $('#nav-above').html(data);

                },
                error: function(data)  
                {  
                alert("Your browser broke!");
                return false;
                }  

            }); 

    }); 
});

    Note that you should respect the requeriements of WordPress in putting the JS script (generally in footer.php before wp-footer() )

    2- Handling the action:

    in functions.php of your theme (or directly in your plugin file), add:

    add_action('wp_ajax_nextPrevious', 'nextPrevious');
add_action('wp_ajax_nopriv_nextPrevious', 'nextPrevious');

    and define in the same file nextPrevious callback function like this:

    function nextPrevious() {

$p= $_GET['id'];
$my_query = new WP_Query();

$my_query->query(array( 'post__in' => array($p)));

if ($my_query->have_posts()) : while ($my_query->have_posts()) : $my_query->the_post(); ?>



 <div class="nav-previous"><?php previous_post_link( '%link', '<img height="34" src="' . get_bloginfo("template_directory") . '/images/previous.png" />' ); ?></div>

<div class="nav-next"><?php next_post_link( '%link', '<img height="34" src="' . get_bloginfo("template_directory") . '/images/next.png" />' ); ?></div>

<?php endwhile;
endif;                  

wp_reset_query();

die();

}

    Do not forget the die function, it is mandatory.

    For more details about AJAX in WordPress, Google first page tutorials are good.