To help explain how this can be achieved, we will be creating a plugin called “Ajax Example“, stored in the folder “ajax-example” inside the plugin directory of your WordPress install.

Further information on creating a WordPress plugin can be found on WordPress.org and other resources, so won’t go into too much detail here.

First we need to create a file called “index.html” and copy the following into this file:

<?php
/*
Plugin Name: Ajax Example
Plugin URI: http://wp.me/pWbfz-dB
Description: Simple example of how to integrate front-end ajax requests via your plugin.
Version: 0.1
Date: 2011-09-01
Author: Steve Whiteley
Author URI: http://flav36rs.com
*/

class Ajax_Example
{
	public function __construct()
	{
		// ...
 	}
}

$ajaxExample = new Ajax_Example();

?>

We will be using the OOP structure for this plugin instead of the prefixed function format, however could be converted with ease. This class provides the skeleton structure of our plugin, you should save this file to our “ajax-example” folder before we start to add more functionality.

The next step is to include the JavaScript file that performs the AJAX request, which is called by the “init” action hook added to the class constructor method:

add_action( 'init', array( &$this, 'init' ) );

Then we add the init function to the plugin, which includes calls to insert the JavaScript file (wp_enqueue_script) and set the parameters required by the external file (wp_localize_script).

public function init()
{
	wp_enqueue_script( 'ajax-example', plugin_dir_url( __FILE__ ) . 'ajax.js', array( 'jquery' ) );
	wp_localize_script( 'ajax-example', 'AjaxExample', array(
		'ajaxurl' => admin_url( 'admin-ajax.php' ),
		'nonce' => wp_create_nonce( 'ajax-example-nonce' )
	) );
}

Additional parameters can be added to array if they are required, the two mentioned should be the minimum that are required.

While we’re here, we should add the function that handles the response generated by the AJAX request. Notice here that we check the nonce value that is defined in the function above and set the content type before returning the encoded JSON array.

public function ajax_call()
{
	if ( ! isset( $_REQUEST['nonce'] ) || ! wp_verify_nonce( $_REQUEST['nonce'], 'ajax-example-nonce' ) )
		die ( 'Invalid Nonce' );
	header( "Content-Type: application/json" );
	echo json_encode( array(
		'success' => true,
		'time' => time()
	) );
	exit;
}

Create “ajax-example/ajax.js” and copy the following snippet into this file. In order to perform the AJAX request, we use the jQuery .getJSON() method. Alternative methods could be used depending on the type of request you are performing.

jQuery.getJSON(
    AjaxExample.ajaxurl,
    {
        action: 'ajax-example',
        nonce: AjaxExample.nonce
    },
    function( response ) {
    	alert( response.success );
    }
);

Unfortunately this won’t actually do anything until we add two hooks to extend the built in AJAX functionality. These are added to the class constructor, the first (wp_ajax_nopriv_ajax-example) provides access for logged in users, the second (wp_ajax_ajax-example) for anonymous / non-logged in visitors.

if ( is_admin() ) {
	add_action( 'wp_ajax_nopriv_ajax-example', array( &$this, 'ajax_call' ) );
	add_action( 'wp_ajax_ajax-example', array( &$this, 'ajax_call' ) );
}

Please be aware that when using these hooks, they are called from within is_admin(), otherwise they are not correctly set.

The full contents of the plugin file “ajax-example/index.php” should be as follows:

<?php
/*
Plugin Name: Ajax Example
Plugin URI: http://wp.me/pWbfz-dB
Description: Simple example of how to integrate front-end ajax requests via your plugin.
Version: 0.1
Date: 2011-09-01
Author: Steve Whiteley
Author URI: http://flav36rs.com
*/

class Ajax_Example
{
	public function __construct()
	{
		if ( is_admin() ) {
			add_action( 'wp_ajax_nopriv_ajax-example', array( &$this, 'ajax_call' ) );
			add_action( 'wp_ajax_ajax-example', array( &$this, 'ajax_call' ) );
		}
		add_action( 'init', array( &$this, 'init' ) );
	}

	public function init()
	{
		wp_enqueue_script( 'ajax-example', plugin_dir_url( __FILE__ ) . 'ajax.js', array( 'jquery' ) );
		wp_localize_script( 'ajax-example', 'AjaxExample', array(
		    'ajaxurl' => admin_url( 'admin-ajax.php' ),
		    'nonce' => wp_create_nonce( 'ajax-example-nonce' )
		) );
	}

	public function ajax_call()
	{
		if ( ! isset( $_REQUEST['nonce'] ) || ! wp_verify_nonce( $_REQUEST['nonce'], 'ajax-example-nonce' ) )
			die ( 'Invalid Nonce' );
		header( "Content-Type: application/json" );
		echo json_encode( array(
			'success' => true,
			'time' => time()
		) );
		exit;
	}

}

$ajaxExample = new Ajax_Example();

?>

Other things to consider when using the example code provided above are that you should probably ensure jQuery is loaded and possibly only add the the scripts to the pages that they are required, rather than globally.

This functionality was tested with WordPress 3.2.1, it may however change and be simplified in future releases.

The option value is a serialized array of the active plugins saved in alphabetical order according to the plugin directory and file name, for example:

Array
(
	[0] => akismet/akismet.php
	[1] => example-plugin/index.php
)

You can however alter the order of the plugins in the array, which will in turn set the order in which the plugins are loaded by WordPress.

The first step towards adjusting the order is to add the following action to your plugin file, which is most likely to be /my-plugin/index.php or /my-plugin/my-plugin.php.

add_action( 'activated_plugin', 'my_plugin_load_first' );

Next you need to include the functionality to perform the actual re-ordering. The following function will fetch the existing list, check that your plugin is in the array and if so remove then append it to the beginning, before finally saving the altered list to the database.

function my_plugin_load_first()
{
	$path = str_replace( WP_PLUGIN_DIR . '/', '', __FILE__ );
	if ( $plugins = get_option( 'active_plugins' ) ) {
		if ( $key = array_search( $path, $plugins ) ) {
			array_splice( $plugins, $key, 1 );
			array_unshift( $plugins, $path );
			update_option( 'active_plugins', $plugins );
		}
	}
}

It should not be necessary for you to adjust anything specified here other than modifying the name of the function used to suit the namespace used by your plugin.

One final thing to consider is only adding this action when the dashboard or administration panels are being displayed, by making use of the is_admin() conditional tag.

Please note that modifying this option is not something I recommend people do unless absolutely necessary, and it my situation it proved to be very useful.

Yesterday saw over 100 downloads as a result of numerous modifications and updates, some of which due to mistakes on my behalf which was mildly irritating. The main reason behind all the updates was to cater for numerous feature requests and bugs reported by users of the plugin.

This plugin – as with Page Meta – was written for a project I have been working on, however there are very few that solve the issue of adding in sub headings / titles and reposition it below the main title (or at least as far as I am aware).

If you have any feedback on this plugin I recommend you post it on the WordPress Plugins forums, otherwise if you’re looking to install this plugin it can be downloaded here.

The plugin quite quickly evolved into a solution that allowed for keywords as well as descriptions to be added, as well as the ability to set a custom page title. If required the page title can even be defined in your page template, allowing for dynamic pages / templates to have specific titles.

Although unsure if anyone would actually be interested in using it, I decided to publish it to the Plugin Directory anyway. If anything it would allow me to manage the versions and easily update the handful of blogs that I have installed it on.

I actually thought that my second plugin, SubHeading would be more popular as there aren’t many existing solutions in the Directory for this. It’s not far behind in downloads, with just over 850 to date.

If you’re looking to create your own plugin and want to get it noticed, it’s recommended that you publish and host it in the directory. Here’s a quick guide to take you through the steps of publishing a plugin on a Windows based system.

1. Download and install Tortoise SVN
2. Request an SVN repository using the Add Your Plugin page (It may take few hours to get your request approved).
3. Once you receive the SVN credentials you will be able to access the repository from http://svn.wp-plugins.org/plugin_name.
4. Checkout the blank repository from your svn account. (This contains three empty folders – branches, tag, trunk). To do this, right click the folder you want to Checkout to and select SVN Checkout.

   

   Enter the URL of your plugin repository and click OK.

   

   Once the process is complete you will see the three folders that have been added.

   

5. Copy the plugin files into the trunk folder and create a readme.txt file if one is not already present.



6. Commit your changes by right clicking the folder and selecting SVN commit.



7. You will be prompted for your authentication details, enter your WordPress.org/bbPress.org username and password (the same one you use on the forums).



8. Now create a tag. Right click on the trunk folder and in the context menu go to TortoiseSVN and choose Branch/Tag. In the dialogue box change the url path from /trunk to /tags/0.1 (or whatever you have stated as the stable tag  in the readme file.



9. Run SVN update on the tags folder (Right click the tags folder and select SVN Update).

Committing a modified plugin / new version

1. Make modifications to the trunk folder.
2. Change the stable tag value in the readme file to the latest stable version, e.g. 0.1.1
3. SVN commit the latest changes in the trunk.
4. Tag the new version (see step 8 above) .
5. SVN update the tags folder.