How and When to Use Actions and Filters

WordPress allows developers to add their own code during the execution of a request by providing various hooks. These hooks come in the form of actions and filters:

Actions: WordPress invokes actions at certain points during the execution request and when certain events occur.

Filters: WordPress uses filters to modify text before adding it to the database and before displaying it on-screen.

action-filters

The number of actions and filters is quite large, so we can’t get into them all here, but let’s at least take a look at how they are used.

Here’s an example of how to use the admin_print_styles action, which allows you to add your own stylesheets to the WordPress admin pages:

add_action('admin_print_styles', 'myplugin_admin_print_styles');

function myplugin_admin_print_styles() {
    $handle = 'myplugin-css';
    $src = MYPLUGIN_PLUGIN_URL . '/styles.css';

    wp_register_style($handle, $src);
    wp_enqueue_style($handle);
}

add_action('admin_print_styles', 'myplugin_admin_print_styles');

function myplugin_admin_print_styles() {

$handle = 'myplugin-css';

$src = MYPLUGIN_PLUGIN_URL . '/styles.css';

wp_register_style($handle, $src);

wp_enqueue_style($handle);

}

And here’s how you would use the the_content filter to add a “Follow me on Twitter!” link to the bottom of every post:

add_filter('the_content', 'myplugin_the_content');

function myplugin_the_content($content) {
    $output = $content;
    $output .= '<p>';
    $output .= '<a href="http://twitter.com/username">Follow me on Twitter!</a>';
    $output .= '</p>';
    return $output;
}

add_filter('the_content', 'myplugin_the_content');

function myplugin_the_content($content) {

$output = $content;

$output .= '<p>';

$output .= '<a href="http://twitter.com/username">Follow me on Twitter!</a>';

$output .= '</p>';

return $output;

}

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How and When to Use Actions and Filters

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