WordPress Plugin Actions
This post was written as part of the How to Write a WordPress Plugin series.
WordPress actions allow you as a plugin author to be able to hook into the WordPress application and execute a piece of code. An example of an action would be that you want a execute some code after a user has published a post or left a comment.
Some of the actions that I use heavily are:
- admin_menu: Allows you to set up an admin panel for your plugin.
- wp_head: Allows you to insert code into the
<head>tag of a blog
Actions in Action
While defining the structure of a WordPress plugin, I left a place holder for some actions. In this example, we are going to set up a piece of code that will run inside the <head> tag of a WordPress blog.
First we need to add a function into our DevloungePluginSeries class.
function addHeaderCode() {
?>
<!-- Devlounge Was Here -->
<?php
}
All the above function does is output an HTML comment. Rather simple, but you could output just about anything. To call this function, we add an action.
//Actions and Filters
if (isset($dl_pluginSeries)) {
//Actions
add_action('wp_head', array(&$dl_pluginSeries, 'addHeaderCode'), 1);
//Filters
}
From the WordPress Plugin API page, the add_action structure is as follows:
add_action ( 'hook_name', 'your_function_name', [priority], [accepted_args] );
Since we are calling a function inside of a class, we pass the action an array with a reference to our class variable (dl_pluginSeries) and the function name we wish to call (addHeaderCode). We have given our plugin a priority level of 1, with lower numbers executed first.
Running the Code
If the Devlounge Plugin Series plugin is activated, the comment of “Devlounge was here” should show up when you go to View->Source in your web browser when looking at your main blog site.
Removing Actions
If your plugin dynamically adds actions, you can dynamically remove actions as well with the remove_actions function. The structure is as follows:
remove_action('action_hook','action_function').
Conclusion
Hopefully this post gave you some insight into what you could do when hooking into WordPress actions. Once again, you can download the code for the sample Devlounge Plugin Series for actions.
Download the Code Used In This Post
For further reading, please check out these links:
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AJ,
One of the readers was curious what plugin you used for showing code. Could you please leave a comment here with the link to the plugin?
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The plugin is iG Syntax hilighter
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Just a tip for anyone who ran into this. The wp_head action wouldn’t work for me at first. Turns out I forgot to add <?php wp_head(); ?> between my html head tags for my theme, so remember to check your theme header template if it doesn’t work for you, all is well now.
Fixed post, the first one stripped out the php.
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Hey, thanks for this series, this is the second time that I’ve referred to it to help me write a plugin. I have come across a problem though. I have a function that test is_single and also if a value in my array is equal to true. This function then hooks into wp_head. However it doesn’t work. I think I might need to make my option variable global, to be able to use it like this? Can you point me in the right direction?
Thanks
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What gives? This will not work for me. I’m running Wp v.2.6.1 I’ve got a call to wp_head() in my theme’s header file, but no matter what I do, it does not add it into the header. Tearing my hair out….
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This appears to be a timing issue. How is wp_head() ever called before a plugin is loaded? According to the call stack, wp_head() has long been executed & written before the web engine gets around to loading up the plugins. So this coding method doesn’t appear to be a way to add css file link to a header. How do you add a plugin’s css file to the main WP header?
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How would I use a wordpress shortcode to display addHeaderCode() ?
Thanks?
Pete
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I appreciate your effort and the quality of the information you provide. I certainly will folow these recommendations!
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Hi all,
Its great that there is someone here to release some helpful information on creating plugins for WordPress. I got here because i’m learning as well! I noticed that some had problems executing their scripts. Anyway, not sure if you had the same problem as me, but my problem was a classic error:
In the second class_exists statement, REMEMBER there is no exclamation.
if ( class_exists(“hunt_order_form”) ) {
NOT
if ( !class_exists(“hunt_order_form”) ) {
Since the class should have been created, you are evaluating to see if the class was created. It was definitely an easy mistake to make if you are like me, typing out the tutorial rather than copy and pasting.
Anyway, not sure if that helped anybody, but hopefully my 1 hour of testing, helped you!
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Suggestion if you ever update this post: Add a section for “using shortcodes”. I had a difficult time figuring this out on my own. For those of you who may need help with this: Look at the shortcode API on codex. Place the “add_shortcode(‘shortcut name’, ‘shortcut function’);” to the same place you put your add_action and add_filter calls:
add_action(‘admin_menu’, ‘DevloungePluginSeries_ap’);
add_action(‘wp_head’, array(&$dl_pluginSeries, ‘addHeaderCode’), 1);
add_action(‘activate_devlounge-plugin-series/devlounge-plugin-series.php’, array(&$dl_pluginSeries, ‘init’));
//Filters
add_filter(‘the_content’, array(&$dl_pluginSeries, ‘addContent’),1);
add_filter(‘get_comment_author’, array(&$dl_pluginSeries, ‘authorUpperCase’));
//Shortcodes
add_shortcode(‘shortcodename’, array(&$dl_pluginSeries, ‘function’));