Get "Hooked" on WordPress Hooks


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An introduction to hooks in WordPress including the Filter Hook, the Action Hook, advanced hook functions, and also implementing custom hooks into your WordPress plugins.

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Get "Hooked" on WordPress Hooks

  1. 1. Get  “Hooked”  on   WordPress  Hooks   November  17,  2013  
  2. 2. MIKESTOWE .com @mikegstowe   •  Open Source Contributor (3 WP Plugins) •  Author, Speaker, and Consultant •  10+ years experience hacking PHP •  Zend Certified PHP 5.3 Software Engineer •  Developer Advocate with Constant Contact
  3. 3. About You… @insert_your_twi8er_handle_here   •  Familiar with WordPress •  Familiar with PHP Code (at least beginner) •  Learning to, have written, or in the process of writing a WordPress Plugin •  Have a GREAT sense of humor
  4. 4. Not You… Insert  Frownie  Face  Here…   No problem!* These slides will be posted online, just go to and start with “PHP for Web Designers,” then do “Building Your WordPress Plugin,” and then feel free to jump to these slides and they should make sense J *Unless you don’t have a sense of humor, nothing I can do for you there…
  5. 5. What  we’re  gonna  talk  about…   What  Are  Hooks   Types  of  Hooks   •   What  are  Hooks   •   The  Filter  Hook   •   How  they  Work   •   The  Ac<on  Hook   •   Code  Considera<ons   •   Advanced  Hooking     •   Custom  Hooks   •   The  Codex  
  6. 6. What  we’re  NOT  talking  about…   This  guy…  
  7. 7. What  are  Hooks?   In  technical  and  strict  terms:  a  Hook  is  an  event,  i.e.   event  as  understood  by  Observer  paIern,  invoked   by  the  do_action() or  apply_filters() call   that  aJerwards  triggers  all  the  ac<on  or  filter   func<ons,  previously  hooked  to  that  event…   h8p://  
  8. 8. What  are  Hooks?   Essen<ally,  the  hook  or  event  triggers  the  appropriate   Observer,  that  takes  an  array  of  “hooked”  func<ons   and  calls  them  using  the  PHP  call_user_func()   func<on,  allowing  for  code  and  opera<ons  to  be   implemented  into  the  core  process  without  modifying   the  core  code.      
  9. 9. A  Rose  by  Any  Other  Name…   Because  Hooks  are  required  by  Ac<ons  and  Filter  you   may  hear  the  phrase  "Ac<on  Hooks"  and  "Filter  Hooks"   used  from  <me  to  <me.   h8p://  
  10. 10. Don’t  let  Hooks  inQmidate  you!   Ok, we might talk about this guy a little bit
  11. 11. *Source code remains untouched for easy upgrades
  12. 12. Hook  Example   <?php add_filter('the_content', 'my_function'); function my_function($content) { return $content . '<p>Share with a Friend!</p>'; } ?> ! The above code creates a very simple “Filter Hook” that adds the text “Share with a Friend!” after each post/ page entry… Yeah, it’s that easy!
  13. 13. *Source code remains untouched for easy upgrades
  14. 14. One  Caveat   Because  your  func<on  called  by  the  hook  becomes  part   of  the  WordPress  code  it  is  important  to  make  sure  you   have  a  unique  name  for  your  func<on.    If  your  func<on   contains  the  same  name  as  another  WordPress  or  plugin   func<on  a  fatal  PHP  error  will  be  thrown,  breaking  your   en<re  site.   start_process()     output()     modify_content()     pluginname_process()     pluginname_output()     pluginname_modify_content()    
  15. 15. FuncQon  Naming  Example   <?php add_filter('the_content', '_trackableshare_process'); function _trackableshare_process($content) { /* ... */ } ?> ! For the Trackable Social Share Icons plugin all functions start with the “_trackableshare_” prefix to prevent confusion with other plugins.
  16. 16. OOP  –  and  You  know  me   If  you  are  using  Object  Oriented  Code,  or  build  your   plugin  as  a  class  you  can  avoid  func<on  naming  concerns   as  your  methods  will  be  separate  from  the  core  func<on   (or  in  another  scope).     However,  you  s<ll  need  to  make  sure  your  class  name  (or   it’s  namespace)  is  unique.  
  17. 17. Class/  Object  Oriented  Example   <?php class trackable_social_share { public function __construct() { // Add Hooks add_filter('the_content', array($this, 'process')); } public function process($content) { /* ... */ } } $trackable_social_share = new trackable_social_share(); ?> ! This is a little bit more complex, and you don’t have to build your plugin this way. This is just an example of the differences.
  18. 18. QuesQons  so  far?   •  A  hook  is  an  event  that  calls  a  func<on  or  a  method  upon  an  ac<on   •  Your  code  is  pulled  into  the  WordPress  code  dynamically,  becoming   part  of  the  site   •  Hooks  are  oJen  referred  to  as  “Ac<on  Hooks”  and  “Filter  Hooks”   •  You  can  use  procedural  or  Object  Oriented  Code  with  Hooks     •  Just  remember  naming  is  key!   •  Pirates  are  bad.  
  19. 19. The  Filter  Hook   The  Filter  Hook  is  designed  modify  content.    Rather   than  being  enacted  on  a  specific  ac<on,  filter   hooks  are  called  when  processing  content,   whether  it  be  for  saving  or  rendering.  
  20. 20. The  Filter  Hook   In  our  previous  examples  we  used  the  filter  hook   to  append  content  to  our  post/  page  content.    This   is  a  perfect  example  of  how  this  hook  works.       We  can  also  manipulate  the  content  using  other   PHP  func<ons  as  wanted.  
  21. 21. Content  ManipulaQon  Example   <?php add_filter('the_content', 'ninjas_vs_pirates'); function ninjas_vs_pirates($content) { return str_replace('Pirates Rule', 'Ninjas Rule', $content); } ?> ! The above code will replace every instance of “Pirates Rule” with “Ninjas Rule” in the page/ post text
  22. 22. Pro  Tip   Don’t  use  Filter  Hooks  to  replace  [shortcodes]…    You  can   do  this  using  str_replace(),  but  WordPress  has  a   built  in  func<on  just  for  short  codes  called   add_shortcode() <?php add_shortcode('pirate', 'ninja_function'); function ninja_function() { return 'ninja'; } ?> !
  23. 23. Filtering  Beyond  Posts   Filters  can  be  used  at  mul<ple  <mes  and  on  mul<ple   types  of  content.    This  means  you  can  modify  the  content   before  storing  it  to  the  database,  or  later  during  the   rendering  phase.    You  may  also  modify  author  data,   comments,  widgets,  links,  blogroll,  dates/<mes,  items  in   the  wp-­‐admin,  etc.  all  dynamically  without  having  to   modify  the  WordPress  core  code. View  all  opQons  at:   h8p://  
  24. 24. Pre-­‐Save  Comment  Filter   <?php add_filter('comment_status_pre ', 'pluginname_noswearwords'); function pluginname_noswearwords($content) { $badwords = array('pirate', 'pirates', 'plank', 'patch', 'hook'); return str_replace($badwords, '*ninja starred*', $content); } ?> ! This code replaces the “bad words” in the array with the text “*ninja starred*” before saving it to the database.
  25. 25. Adding  Filter  Hooks   All  Filter  Hooks  are  added  using  the  add_filter()  func<on:   add_filter( $tag, $function, [$priority], [$accepted_args] ) Tag:  (string)  What  type  of  content  process  the  filter  should  be  applied  to     FuncQon:  (callback)  The  func<on  to  be  run     Priority:  (int)  –  op<onal  Order  in  which  it  should  be  run,  the     lower  the  number  the  sooner  it  will  be  executed,  default  is  10     Accepted  Args:  (int)  –  op<onal  Number  of  accepted  arguments     when  using  WP  >=  1.5.1  and  a  matching  apply_filters() call.       Default  is  1 hIp://<on_Reference/add_filter  
  26. 26. In  PracQce   <?php add_filter('the_content', 'pirates_rule'); add_filter('the_content', 'ninjas_rule', 9); add_filter('the_content', 'you_rule', 8); function pirates_rule($content) { return str_replace('who_rules', 'Pirates Rule', $content); } function ninjas_rule($content) { return str_replace('who_rules', 'Ninjas Rule', $content); } function you_rule($content) { return str_replace('who_rules', 'You Rule', $content); } ?> ! Assuming our blog post text is just “who_rules,” what would be the output of this code?
  27. 27. Rock  Star!   The  correct  answer  is  “You  Rule”  as  this  has  the   highest  priority.     Since  we  are  running  a  string  replace   (str_replace()),  this  will  replace  the   who_rules  text  with  “You  Rule”  leaving  nothing  for   pirates_rule  or  ninjas_rule  to  replace!  
  28. 28. In  PracQce  –  Trick  QuesQon   <?php add_filter('the_content', 'pirates_rule'); add_filter('the_content', 'ninjas_rule', 9); add_filter('the_content', 'you_rule', 8); function pirates_rule($content) { return 'Pirates Rule'; } function ninjas_rule($content) { return 'Ninjas Rule'; } function you_rule($content) { return 'You Rule'; } ?> ! Assuming our blog post text is just “who_rules,” what would be the output of this code?
  29. 29. You  Can’t  Be  Tricked!   The  correct  answer  is  “Pirates  Rule”  as  this  has  the   lowest  priority  (default  of  10).     This  <me  we  aren’t  replacing  any  set  of  text,  but   are  actually  overwri<ng  the  content  of  the  post   completely!    First  we  overwrote  the  text  with  “You   Rule”,  then  we  overwrote  that  with  “Ninjas   Rule,”  and  finally,  because  it  was  executed   last  we  overwrote  the  text  with  “Pirates   Rule!”  
  30. 30. Thank  ya,  Thank  ya  very  much   Thank ya, thank ya very much
  31. 31. The  AcQon  Hook   The  Ac<on  Hook  is  triggered  in  WordPress  when  an   ac<on  event  takes  place,  such  as  loading  a  page   (front-­‐end  or  admin),  inser<ng  comments,  saving   blog  posts,  or  even  switching  themes.  
  32. 32. The  AcQon  Hook   For  example,  when  loading  header,  footer,  or  even   the  admin  menu  an  Ac<on  Hook  is  triggered.     Likewise,  when  crea<ng  a  post  the  admin_init   Ac<on  Hook  is  called,  and  when  saving  it  the   save_post  Ac<on  Hook  is  called.  
  33. 33. The  AcQon  Hook   The  Ac<on  Hook  is  designed  to  provide  greater   flexibility  in  how  items  are  processed  as  well  as  the   ability  to  add  addi<onal  features  to  the  WordPress   system  (such  as  addi<onal  text  fields  when   crea<ng  or  edi<ng  a  post),  adding  JavaScript/   Stylesheets,  and  other  items.  
  34. 34. AcQon  Hook  Example   <?php add_action('admin_menu', 'my_new_plugin_add_admin_menu_item'); function my_new_plugin_add_admin_menu_item() { if(function_exists('add_submenu_page')) { add_submenu_page('plugins.php','My New Plugin', 'My New Plugin', 10, 'my_new_plugin', 'my_new_plugin_admin_page_function'); } } ?> ! The above code adds a new menu item to the admin menu when it is built, allowing us to create an admin page for our Plugin if desired.
  35. 35. AcQon  Hook  Example   The  AcQon:  Get  Admin  Menu         The  Request:  While  building  the  Admin  Menu,  Run  this   func<on  that  adds  an  addi<onal  item  under  the  Plugins   sec<on.         The  Result:  The  menu  is  generated  with  our     requested  link  included  under  the  Plugin  Sec<on.   When  the  link  is  clicked  the  func<on  we  set  in  the   add_submenu_page()  or     my_new_plugin_admin_page()  will  be  used  to   generate  the  admin  page  for  our  plugin.
  36. 36. AcQon  Hook  Example  #2   <?php add_action('admin_init', 'add_pirate_comments', 1); function add_pirate_comments() { add_meta_box( 'pirate_comments', __( 'What does the Pirate Say', 'pirate_text' ), ‘pirate_text_box_function’, 'post', 'normal', 'high' ); } ?> ! The above code adds a new meta Create/ Edit post screen in the admin panel box based on the pirate_text_box_function() using the add_meta_box() function
  37. 37. Pro  Tip   The  __()  func<on  is  the  Translate  func<on  for  WordPress.     By  pumng  your  text  in  this  func<on  WordPress  will  use   the  translate()  func<on  to  grab  the  proper  text  based  on   the  locale  of  your  user. <?php add_action('admin_init', 'add_pirate_comments', 1); function add_pirate_comments() { add_meta_box( 'pirate_comments', __( 'What does the Pirate Say', 'pirate_text' ), ‘pirate_text_box_function’, 'post', 'normal', 'high' ); } ?> ! hIp://<on_Reference/_2  
  38. 38. Pro  Tip   This  means  for  some  locales  we  could  have  the  text   “What  does  the  Pirate  Say”  actually  be… hIp://<on_Reference/_2  
  39. 39. Pro  Tip   This  means  for  some  locales  we  could  have  the  text   “What  does  the  Pirate  Say”  actually  be… Or  whatever  the  heck  the  Fox  says… hIp://<on_Reference/_2  
  40. 40. AcQon  Hook  Example  #3   <?php add_action('save_post', 'my_plugin_save_post_data'); function _trackableshare_save_box_postdata($id) { // Save logic goes here where $id is the ID of the post } ?> ! The above code calls the my_plugin_save_post_data() function when a post is created or updated. There we can store the data where-ever we need to.
  41. 41. Adding  AcQon  Hooks   All  Ac<on  Hooks  are  added  using  the  add_ac<on()  func<on:   add_action( $tag, $function, [$priority], [$accepted_args] ) Tag:  (string)  What  type  of  content  process  the  filter  should  be  applied  to     FuncQon:  (callback)  The  func<on  to  be  run     Priority:  (int)  –  op<onal  Order  in  which  it  should  be  run,  the     lower  the  number  the  sooner  it  will  be  executed,  default  is  10     Accepted  Args:  (int)  –  op<onal  Number  of  accepted  arguments     when  using  WP  >=  1.5.1  and  a  matching  apply_filters() call.       Default  is  1 hIp://<on_Reference/add_ac<on  
  42. 42. QuesQons  so  far?   •  Filter  Hooks  are  designed  to  modify  Content.    Ac<on  Hooks  are   designed  to  add  or  remove  Code  in  that  ac<on.   •  Filter  hooks  are  added  using  the  add_filter()  func<on   •  Ac<on  hooks  are  added  using  the  add_ac<on()  func<on   •  Priority  is  important!    Remember  a  lower  number  is  more  important   priority  wise  than  a  higher  number.   •  We  do  not  really  know  what  the  Fox  says.  
  43. 43. Advanced  Hooking   WordPress  also  provides  several  func<ons  for   determining  what  func<ons  have  been  hooked  to  a   filter,  if  the  hook  has  already  been  triggered,   removing  func<ons  from  hooks,  and  even   removing  all  func<on  calls  from  a  hook.  
  44. 44. AcQon  Based  FuncQons   has_action(‘hook’, ‘function’); did_action(‘hook’); remove_action(‘hook’, ‘function’); remove_all_actions(‘hook’);
  45. 45. Filter  Based  FuncQons   has_filter(‘hook’, ‘function’); did_filter(‘hook’); current_filter(); remove_filter(‘hook’, ‘function’); remove_all_filters(‘hook’);
  46. 46. has_*   The  has_action() and  has_filter() func<ons   detect  whether  or  not  a  func<on  has  been  added  to  the   array  of  hooks  for  that  par<cular  event.     This  will  return  boolean  true  or  false.  
  47. 47. did_*   The  did_action() and  did_filter() func<ons   detect  whether  or  not  the  event  has  been  triggered.    If   your  event  was  not  hooked,  but  the  event  was  run  it  will   s<ll  return  true  as  it  is  not  func<on  specific.     This  will  return  boolean  true  or  false.  
  48. 48. current_filter   The  current_filter() func<on  returns  the  current   event  that  is  being  processed.    For  example,  if  the  hook   triggered  was  “the_content,”  this  func<on  would  return   “the_content.”         This  is  especially  useful  when  using  one  func<on  or   method  to  handle  mul<ple  types  of  filter  events.  
  49. 49. remove_*   The  remove_action() and  remove_filter() func<ons  will  remove  a  specific  func<on  from  a  specific   ac<on  or  filter  hook.     This  is  useful  if  you  no  longer  want  the  func<on  to  be   called  when  the  event  is  triggered.  
  50. 50. remove_all_*   The  remove_all_actions() and   remove_all_filters() func<ons  will  remove  all   associated  func<ons  from  an  ac<on  hook  or  filter  hook.     This  func<on  takes  the  ‘hook’  as  the  first  parameter,  and   also  accepts  a  second,  op<onal  parameter  that  is     priority  specific.    For  example,  if  you  wanted  to     remove  all  items  from  the_content  with  a  priorit   of  4:     remove_all_filters(‘the_content’, 4);
  51. 51. CreaQng  Custom  Hooks   You  can  also  setup  custom  hooks  in  your  plugin  or  theme   that  can  be  hooked  into  by  other  plugins  using  the   do_ac<on()  and  apply_filters()  func<ons.   do_action(‘hook_name’); apply_filters(‘hook_name’, $content); ‘hook_name’  is  the  name  you  created  for  your  new  hook,   such  as  ‘my_plugin_init’  or  ‘my_plugin_content’  
  52. 52. Adding  Custom  Hooks   <?php function my_plugin_function() { // Allow hooks into this function do_action('my_plugin_init'); // Create Content $content = 'Hello world'; // Allow Content to have filters ran against it // Be sure to store the returned result of the FILTER!!! $content = apply_filters('my_plugin_content', $content); } ?> !
  53. 53. QuesQons?   •  WordPress  provides  several  func<ons  that  we  can  use  to  modify   hooks  even  aJer  using  the  add_filter()  or  add_ac<on()  func<ons.     •  WordPress  also  allows  you  to  create  custom  Hooks  within  your   plugin  or  theme   .   •  When  crea<ng  a  custom  Filter  Hook  it  is  important  to  remember  to   store  the  result  as  the  filtered  content  will  be  passed  back  through   the  apply_filters()  func<on.     •  This  sec<on  wasn’t  very  funny.  
  54. 54. Use  the  Codex   We’ve  covered  a  lot  of  informa<on  about  WordPress  hooks,  and   there  is  a  LOT  more  informa<on  available  on  the  WordPress  Codex,   including  the  types  of  params  certain  hooks  will  send  to  your  hooked   func<on  when  that  event  is  triggered.     You  can  learn  about  the  different  Filter  Hooks  at:   hIp://     And  AcQon  Hooks  at:     hIp://<on_Reference     Of  course,  always  remember  the  main  Codex  URL:   h8p://  
  55. 55. A  Final  Thought…  
  56. 56. A  Final  Thought…   And  Kaygo  likes  music  L    Don’t  be  a  pirate.  
  57. 57. THANK YOU. A big thank you to Constant Contact for making this presentation possible @mikegstowe @ctct_api visit  for  more  on  PHP  and  Web  Development  
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