A Deep Understanding of WordPress Actions and Filters

WordPress is known for its extensibility – the ability to change the behaviour of the software without breaking the core code. This is added through plugins and themes.

Understanding how to extend WordPress is essential if you want to develop solutions using WordPress. This talk will teach you how actions and filters work, with some practical and theoretical examples to illustrate their functionality.

Attendees should hopefully come away from this talk with a greater understanding on how actions and filters, or hooks as they are collectively known, can unlock the door to building greater things with WordPress, and as I worked out being able to say “Wow, you can do (almost) anything with WordPress!”.

Transcript

1. @wpmark
   https://highrise.digital
   A Deep Understanding of
   WordPress Actions and
   Filters
   Mark Wilkinson (@wpmark)
   WordCamp Edinburgh
   July 2017
   

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2. @wpmark
   https://highrise.digital
   Mark Wilkinson
   Using & building
   WordPress sites for over
   10 years as a WordPress
   developer
   Owner of Highrise
   Digital
   Follow me: @wpmark
   

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3. @wpmark
   https://highrise.digital
   What are actions/filters?
   How do they work?
   Examples
   Making your code
   extensible
   

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4. @wpmark
   https://highrise.digital
   What are actions/filters?
   How do they work?
   Examples
   Making your code
   extensible
   

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5. @wpmark
   https://highrise.digital
   What are actions/filters?
   How do they work?
   Examples
   Making your code
   extensible
   

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6. @wpmark
   https://highrise.digital
   What are actions/filters?
   How do they work?
   Examples
   Making your code
   extensible
   

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7. @wpmark
   https://highrise.digital
   Simply put, hooks are what give us
   the ability to customize, extend, and
   enhance WordPress through an API in
   our themes, plugins, and other
   custom development efforts.
   Tom McFarlin, 2012
   https://code.tutsplus.com/articles/the-beginners-guide-to-wordpress-actions-and-filters--wp-27373
   

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8. @wpmark
   https://highrise.digital
   Simply put, hooks are named events,
   run in the WordPress code that allow
   us (developers) to run our own code at
   these points in time.
   Mark Wilkinson, 2017
   

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9. @wpmark
   https://highrise.digital
   WordPress
   Page
   Life Cycle
   • Inspects the URL
   • Queries DB for that
   content
   • Queries DB for related
   data (taxonomies,
   images etc.)
   • Loads correct template
   file
   • Outputs the content
   within the theme
   template
   

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10. @wpmark
    https://highrise.digital
    @Rarst
    https://www.rarst.net/
    wordpress/wordpress-core-
    load/
    

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11. @wpmark
    https://highrise.digital
    How do they work?
    

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12. @wpmark
    https://highrise.digital
    They are a bit like a
    shopping list
    

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13. @wpmark
    https://highrise.digital
    Shopping List
    Bread
    Milk
    Cereal
    Biscuits
    

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14. @wpmark
    https://highrise.digital
    Shopping List
    Bread
    Milk
    Cereal
    Biscuits
    Beer
    

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15. @wpmark
    https://highrise.digital
    Shopping List
    Bread
    Milk
    Cereal
    Biscuits
    Beer
    Wine
    

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16. @wpmark
    https://highrise.digital
    Shopping List
    Bread
    Milk
    Biscuits
    Wine
    

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17. @wpmark
    https://highrise.digital
    Hooks
    Actions & Filters
    

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18. @wpmark
    https://highrise.digital
    Hooks
    Actions & Filters
    

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19. @wpmark
    https://highrise.digital
    do_action();
    add_action();
    remove_action();
    

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20. @wpmark
    https://highrise.digital
    do_action(
    'action_name',
    $args
    );
    

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21. @wpmark
    https://highrise.digital
    add_action(
    'action_name',
    $function,
    $priority,
    $accepted_args
    );
    

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22. @wpmark
    https://highrise.digital
    Action Example
    

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23. @wpmark
    https://highrise.digital
    save_post();
    save_post_{$post_type};
    

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24. @wpmark
    https://highrise.digital
    /wp-includes/post.php
    do_action( 'save_post', $post_ID, $post, $update );
    

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25. @wpmark
    https://highrise.digital
    /wp-includes/post.php
    do_action( 'save_post', $post_ID, $post, $update );
    function wpmark_on_save_post( $post_ID, $post, $update ) {
    update_post_meta( $post_ID, ‘meta_key’, ‘meta_value’ );
    }
    add_action( ‘save_post', ‘wpmark_on_post_save’, 10, 3 );
    

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26. @wpmark
    https://highrise.digital
    /wp-includes/post.php
    do_action( 'save_post', $post_ID, $post, $update );
    function wpmark_on_save_post( $post_ID, $post, $update ) {
    update_post_meta( $post_ID, ‘meta_key’, ‘meta_value’ );
    }
    add_action( ‘save_post', ‘wpmark_on_post_save’, 10, 3 );
    do_action( ‘save_post_product’, $post_ID, $post, $update );
    

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27. @wpmark
    https://highrise.digital
    Hooks
    Actions & Filters
    

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28. @wpmark
    https://highrise.digital
    apply_filters();
    add_filter();
    remove_filter();
    

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29. @wpmark
    https://highrise.digital
    apply_filters(
    'filter_name',
    'filterable_thing',
    $args
    );
    

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30. @wpmark
    https://highrise.digital
    add_filter(
    'filter_name',
    $function,
    $priority,
    $accepted_args
    );
    

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31. @wpmark
    https://highrise.digital
    Filter Example
    

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32. @wpmark
    https://highrise.digital
    

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33. @wpmark
    https://highrise.digital
    /wp-admin/edit-form-advanced.php
    apply_filters( 'enter_title_here', __( 'Enter title here' ), $post );
    

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34. @wpmark
    https://highrise.digital
    function wpmark_title_here( $title, $post ) {
    if ( 'post' === get_post_type( $post ) ) {
    $title = __( 'Article Title' );
    }
    return $title;
    }
    add_action( 'enter_title_here', ‘wpmark_title_here’,10, 2 );
    apply_filters( 'enter_title_here', __( 'Enter title here' ), $post );
    /wp-admin/edit-form-advanced.php
    

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35. @wpmark
    https://highrise.digital
    function wpmark_title_here( $title, $post ) {
    if ( 'post' === get_post_type( $post ) ) {
    $title = __( 'Article Title' );
    }
    return $title;
    }
    add_action( 'enter_title_here', ‘wpmark_title_here’, 10, 2 );
    apply_filters( 'enter_title_here', __( 'Enter title here' ), $post );
    /wp-admin/edit-form-advanced.php
    

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36. @wpmark
    https://highrise.digital
    Making your own
    code extensible
    

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37. @wpmark
    https://highrise.digital
    Setting up arrays
    $job_posts = new WP_Query(
    array(
    ‘post_type’ => ‘wpmark_job’,
    ‘posts_per_page => 12
    )
    );
    

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38. @wpmark
    https://highrise.digital
    Setting up arrays
    $job_posts = new WP_Query(
    apply_filters(
    ‘wpmark_job_post_query_args’,
    array(
    ‘post_type’ => ‘wpmark_job’,
    ‘posts_per_page => 12
    )
    )
    );
    

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39. @wpmark
    https://highrise.digital
    In Loops
    while ( $job_posts->have_posts() ) : $job_posts->the_post();
    do_action( ‘wpmark_job_post’, $post );
    endwhile;
    

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40. @wpmark
    https://highrise.digital
    Function returns
    function wpmark_sub_title( $post_id = 0 ) {
    return get_post_meta( $post_id, ‘subtitle’, true );
    }
    

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41. @wpmark
    https://highrise.digital
    Function returns
    function wpmark_sub_title( $post_id = 0 ) {
    return apply_filters(
    ‘wpmark_sub_title’,
    get_post_meta( $post_id, ‘subtitle, true ),
    $post_id
    );
    }
    

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42. @wpmark
    https://highrise.digital
    Recap
    

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43. @wpmark
    https://highrise.digital
    do_action();
    apply_filters();
    

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44. @wpmark
    https://highrise.digital
    add_action();
    add_filter();
    

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45. @wpmark
    https://highrise.digital
    Remember
    Filters - always return
    the ‘filterable thing’!
    

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46. @wpmark
    https://highrise.digital
    Try to make your own
    code extensible
    Using do_action() &
    apply_filters()
    

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47. @wpmark
    https://highrise.digital
    Thank you for
    listening
    Questions?
    @wpmark
    

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