See hooks in action

To see this functionality in action, check out the source code of one of your web pages when the wp_head() hook is present in your header.php file (as it should be by default). Then remove the hook, reload the page, and check the source again. You will see that it is the wp_head() hook that enables those markup-generating functions to operate as intended.

Getting precise with custom hooks

In a similar vein, other areas of your theme may also be targeted with WordPress hooks. We have already mentioned the wp_footer() hook, which is useful for adding scripts, copyright information, and database statistics to the bottom of your pages. Indeed, you can apply targeted functionality to any of the currently available WordPress hooks, but many times it’s just as easy to create your own hook and place it exactly where you need it. Whether you are writing a plugin or implementing some custom functions.php goodness, custom hooks enable precision targeting anywhere within your theme, making it more flexible and easier to customize. Let’s look at an example..

An example of how custom hooks are used

At Perishable Press, I provide my guests with nearly twenty alternate themes that may used while visiting the site. Each of these themes is visually and functionally unique, requiring different sets of plugins and custom scripts in order to function properly. To get the plugins to play nice together and target only select groups of themes, I take advantage of WordPress’ custom-hook functionality. For example, I have a stats plugin that needs to hook into wp_head() for a few of my themes, but using that specific hook would result in conflicting scripts in some of the other themes. Thus, I added a custom hook in the header of the themes that require the stat plugin’s functionality. Other themes are not affected and everything clicks along like clockwork.

Creating and using custom hooks

Creating and using custom hooks is surprisingly simple. You basically need to define the hook in your functions.php (or plugin) file, and then place the hook tag in the desired location within your theme. Thus:

Step 1: Define your custom hook

Add this to your functions.php file:

// i can has custom hook
function custom_hook() {
	do_action('custom_hook');
}

This will add an action named “custom_hook” to WordPress’ hook library, enabling you to use it anywhere in your theme template. Of course, you should name your custom hook something that makes sense for your particular application. Once that is in place, move on to the next step.

Step 2: Tag your custom hook

Place the function call in the desired location within your theme template:

<?php custom_hook(); ?>

That’s all there is to it. With those two snippets of code in place, your theme is equipped with a custom hook through which you may execute any function you wish using WordPress’ powerful add_action() feature.

Step 3: Add your function

To keep things simple, we’ll use a very basic function to illustrate this step. In your functions.php file, add the following code:

<?php 
function hello_wordpress() {
	echo '<h1>Hello WordPress!</h1>';
}
add_action('custom_hook', 'hello_wordpress', 7);
?>

This function will echo “Hello WordPress!” on your web page at the location of your custom_hook() in your theme template. To really get a sense of how WordPress hooks work, try moving the <?php custom_hook(); ?> tag to a different location within your theme and watch the output text move accordingly. Amazing, but true.

The key to using your custom hook for one of your functions is the following line:

add_action('custom_hook', 'hello_wordpress', 7);

This is where you actually associate your function with the custom hook. The first parameter is the name of the custom hook, the second parameter is the name of the function, and the third parameter sets the priority of the function. When multiple functions are targeting the same hook, the priority specifies the order in which the action should be performed. The default priority value is “10”.

Take-home message

If nothing else, just remember that WordPress action hooks provide a way for you to output content virtually anywhere in your theme. Chances are that there is already a default hook that will do the job, but if not, the information in this tutorial will enable you to create and use custom hooks as needed to get the job done.

That does it for this fine DiW tutorial. Be sure to subscribe to our feed for more great WordPress content delivered fresh to your feed reader!

© 2009 Digging into WordPress | Permalink | 11 comments | Add to del.icio.us | Post tags: actions, functions, hooks, plugin, Theme