Actions filters
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The document discusses WordPress actions and filters. Actions allow plugins to hook into points of execution, while filters allow plugins to modify data before it is used. It provides examples of how to use add_action(), add_filter(), remove_action(), remove_filter() and has_action/filter(). Common core actions and filters are also listed, such as init, wp_head, the_content, and the_title. The purpose is to demonstrate how plugins can leverage hooks to customize WordPress behavior.
Actions filters
- 1. Hooked on WordPress Actions and Filters
- 2. John Dillick @johndillick Core developer on Shopp e-commerce plugin for WordPress Developing for and supporting WordPress for 3 years Technical writer and information sponge. Not a design guy; Leave graphics and design to other guys.
- 3. Who’s this for? Desire to extend and customize WordPress Some PHP knowledge Not already a WordPress plugin developer, or just need a place to sit and zone out for 45 minutes. Don’t mind hearing me say “Um” at least a thousand times. I’m not a professional speaker.
- 4. WTF are actions/filters RTFM - see http://codex.wordpress.org/ Plugin_API Actions are points of execution in WordPress that your plugin can “hook” code to execute. Filters give your code an opportunity to add/ remove/modify data before it will be used by WordPress and other plugins.
- 5. What actions/filter are out there? Short answer: Too many to cover in 45 minutes. Covering some important ones; Dig into codex and WordPress code itself to discover amazing possibilities. Covering what the hooks look like, syntax stuff, and how to leverage them.
- 6. Actions, why? Devs think, ‘wouldn’t it be nice to have “this” happen when “that” happens?’ One way to do this: modify WordPress code directly. NO! Actions are provided by the developer of a particular feature of WordPress to give you an opportunity to do “something” too. Often provide you an opportunity to put things into motion before, during, or after another action
- 7. What does an action “hook” look like? <?php do_action(‘action_name’); ?> <?php do_action_ref_array(‘action_name’,$args); ?>
- 8. How to hook in: If the “hook” name in WP is ‘do_this’: <?php do_action(‘do_this’); ?> You hook in by providing a “callback” (function name): <?php add_action(‘do_this’,‘my_function’); ?>
- 9. Callbacks Quick PHP review, a callback is: 1. String name of a function: ‘funk’ <?php function funk () {} ?> <?php //callback add_action(‘do_something’,‘funk’);
- 10. Callbacks, cont. 2. An array with an Object and a string function name. <?php class A { function funk () {} } $A = new A(); //callback for $A->funk(); add_action( ‘do_something’, array($A,‘funk’) ); ?>
- 11. Callbacks, cont. 3. An array with a class name and a string static function name. <?php class B { static function funk () {} } //callback for B::funk(); add_action( ‘do_something’, array(‘B’,‘funk’) ); ?>
- 12. Callbacks, cont. 3. Callback returned from a function, such as create_function() <?php // callback for anonymous function $my_func = create_function(“$args”,”echo ‘hello world!’;”); add_action( ‘do_something’, $my_func ); ?>
- 13. add_action() The full form: <?php add_action( $tagname, $callback, $priority, $argcount ); ?>
- 14. add_action() cont. $priority: (Default 10) The smaller the number, the quicker your function will happen, the bigger, the later. $argcount: (Default 1) If the action passes 1 or more arguments as useful data, you can tell how many you want passed to your callback.
- 15. do_action() example <?php //your code add_action(‘hello_set’,’a’,10,1); add_action(‘hello_set’,’b’,1); function a ( &$hello ) { $hello = ‘hola, el mundo’; } function b () { exit(); } ?> <?php // Primitive action hook, pretend it’s in WordPress $hello = ‘hello world’; do_action(‘hello_set’, $hello); echo $hello; ?>
- 16. What output? Answer: Nothing Because function ‘b’ was called with a higher priority, and exited, ‘a’ never ran... nor anything else afterwards. All plugins have an opportunity to break all other plugins at some point. Use standard WordPress function calls whenever possible.
- 17. Filtering WordPress is using some data to do something, for instance, to output the body of a post on my blog. As a developer, I want to be able to add, remove, or modify that data before WordPress uses it.
- 18. How to filter: If the “filter” tag name in WP is ‘the_content’: <?php apply_filters(‘the_content’,$postcontent); ?> You hook in by providing a “callback”, just like with actions hooks. <?php add_filter(‘the_content’,‘my_function’); ?> my_function will always expect at least one arg, and will always return an arg.
- 19. Full filter syntax add_filter($tagname, $callback, $priority, $num_of_args); Your filter is expected to return something. Forgetting to return something will certainly break something.
- 20. Wordpress with ‘P’! Back in 2010, WordPress decided to take measures to ensure the WordPress trademark was used properly. <?php add_filter(‘the_content’,‘capital_P_dangit’); add_filter(‘the_title’,‘capital_P_dangit’); add_filter(‘comment_text’,‘capital_P_dangit’); ?>
- 21. If I had core commit... ... you would all know. <?php function john_dillick_rocks ( $content ) { ! $content = str_replace(‘Dillick sucks’,‘Dillick rocks’,$content); ! return $content . ‘ - BTW, you know John Dillick rocks, right?’; } add_filter(‘the_content’,‘john_dillick_rocks’); add_filter(‘the_title’,‘john_dillick_rocks’); add_filter(‘comment_text’,‘john_dillick_rocks’); ?>
- 22. Removing Action/Filter remove_action($tag,$callback,$priority,$nargs); remove_filter($tag,$callback,$priority,$nargs); remove_all_actions($tag,$priority); remove_all_filters($tag,$priority); <?php foreach ( array(‘the_content’,‘the_title’,‘comment_text’) as $tag ) { ! remove_action($tag,’capital_P_dangit’); ! // remove_action($tag,‘john_dillick_rocks’); }
- 23. Check for an action/filter has_action($tag,$callback); has_filter($tag,$callback); <?php function enlightened () { ! if ( has_filter(‘the_content’,‘john_dillick_rocks’) ) ! ! echo “<p>This site powered by Sasquatch.</p>”; ! else echo “<p>Nothing to see here. Move along.</p>”; } add_action(‘wp_footer’,’enlightened’); ?>
- 24. Common Actions add_action(‘init’,$callback); Early action for plugin initialization. add_action(‘admin_init’,$callback); Called on admin initialization.
- 25. Common Actions add_action(‘wp_head’,$callback); Called in theme when page header is output. add_action(‘admin_head’,$callback); Called in admin when page header is output. add_action(‘wp_footer’,$callback); Called in theme when page footer is output. add_action(‘admin_footer’,$callback); Called in admin when page footer is output.
- 27. Common Filters add_filter(‘the_content’,$callback); Filters post and page content. add_filter(‘the_excerpt’,$callback); Filters post and page excerpt content.
- 28. Common Filters add_filter(‘the_title’,$callback); Filters post and page content titles. add_filter(‘wp_title’,$callback); Filters blog page title.