Beginning WordPress Plugin Development

Beginning WordPress Plugin Development Aizat Faiz aizat.faiz@gmail.com

Download and view at http://blog.aizatto.com/?p=3729

Creative Commons http://www.flickr.com/photos/kwl/4435490471/

By Attribution http://www.flickr.com/photos/balakov/4571468943/

Aizat Faiz http://www.flickr.com/photos/byte/3397174843/ [email_address]

Your Friends / Resources http://www.flickr.com/photos/balakov/4571468943/

WordPress Codex
http://codex.wordpress.org

WordPress Plugin Directory

Google
http://www.google.com.my

What is a Hook? http://www.flickr.com/photos/kwl/4247555680/

WordPress is the Base http://www.flickr.com/photos/kwl/4247555680/

Plugins are the Blocks http://www.flickr.com/photos/sixteen-miles/3757674953/

Hooks are the Pegs http://www.flickr.com/photos/linuxmatt/92802487/

Actions Filters 2 Kinds of WordPress Hooks

Actions

Actions Actions are the hooks that the WordPress core launches at specific points during execution, or when specific events occur. Your plugin can specify that one or more of its PHP functions are executed at these points, using the Action API.
http://codex.wordpress.org/Plugin_API#Actions
http://codex.wordpress.org/Plugin_API/Action_Reference

Actions Actions = “Do Something”

Filters

Filters Filters are functions that WordPress passes data through, at certain points in execution, just before taking some action with the data (such as adding it to the database or sending it to the browser screen). Filters sit between the database and the browser (when WordPress is generating pages), and between the browser and the database (when WordPress is adding new posts and comments to the database); most input and output in WordPress passes through at least one filter. WordPress does some filtering by default, and your plugin can add its own filtering http://codex.wordpress.org/Plugin_API#Filters http://codex.wordpress.org/Plugin_API/Filter_Reference

Filters Filters = Transform

Actions and Filters Actions = “Do Something” Filters = Transform

1133 hooks
* as of WordPress v2.9

Problem: Finding the Right Hook for the Right Job

Hard to Recommend
Look at the resources I gave you
WordPress Codex
WordPress Plugin Directory
Google
Action and Filter Reference
http://codex.wordpress.org/Plugin_API/Action_Reference
http://codex.wordpress.org/Plugin_API/Filter_Reference

Writing Your First Plugin

WordPress Directory Structure All Plugins are stored in: /wp-content/plugins/

Plugin Directory Structure
Your Plugin:
/wp-content/plugins/my-plugin
Inside “ my-plugin ”
readme.txt
screenshot-1.png
my-plugin.php
Always put it in a directory!
Uses 'dashes' and not 'underscores'
http://codex.wordpress.org/Writing_a_Plugin#Names.2C_Files.2C_and_Locations

readme.txt http://codex.wordpress.org/Writing_a_Plugin#Readme_File http://wordpress.org/extend/plugins/about/readme.txt Useful only for publishing to WordPress Plugin Directory Information about your plugin: Description, Installation, Changelog, Donation Links, Tags, etc...

screenshot-1.png Useful only for publishing to WordPress Plugin Directory

my-plugin.php Your Plugin Code
4 parts to a plugin
Plugin Header
Hooks
PHP Code
Template Code

File Structure

Plugin Headers http://codex.wordpress.org/Writing_a_Plugin#Standard_Plugin_Information

Plugin Headers http://codex.wordpress.org/Writing_a_Plugin#Standard_Plugin_Information
Always on top, no choice
Fill in with your own details

Hooks (Filters)

Hooks (Filters)
After plugin headers (my preferance)
Makes it easier to find

PHP Code

Plugin 1 Figure out what you want to do. I want to convert all instances of “WordPress” to “WORDPRESS” in a post's content.

the_content (filter) http://codex.wordpress.org/Plugin_API/Filter_Reference/the_content

add_filter http://codex.wordpress.org/Plugin_API/Filter_Reference/the_content

add_filter http://codex.wordpress.org/Plugin_API#Hook_to_WordPress ② ① Hook Name ② Callback ①

Hook Callback
Determines what PHP function to call
Callback can be either:
String; or
Array of 2 strings (my preference)

Hook Callback
String
Calls a function
Array of 2 strings
Calls a static function in a class

They do the same thing

I Prefer Array Callbacks
Allows me to segment my code
Lower chances of name conflicts
Easily tell which function belongs to which hook

Filters are Transformations filters have to return a transformation

Filter return Values
A filters return value, is the result of the transformation
② ① return ② transformation ① http://php.net/manual/en/function.preg-replace.php

Plugin 2 Figure out what you want to do. I want to BOLD all instances of “WORDPRESS” in a post's content.

Hook Priority http://codex.wordpress.org/Plugin_API#Hook_to_WordPress

Priority ② ② Callback ① ③ ② ② ③ Priority (optional) ① Hook Name http://codex.wordpress.org/Plugin_API#Hook_to_WordPress

Which one goes first? WordPress2WORDPRESS#the_content ABolderWordPress#the_content

Default Priority 10 smaller numbers = higher priority larger numbers = lower priority http://codex.wordpress.org/Plugin_API#Hook_to_WordPress

Therefore Order of execution: (10) WordPress2WORDPRESS#the_content (20) ABolderWordPress#the_content

Plugin 3 Figure out what you want to do. I want to add a class, to represent a post that has more than 10 comments

accepted_args http://codex.wordpress.org/Plugin_API#Hook_to_WordPress

accepted_args http://codex.wordpress.org/Plugin_API#Hook_to_WordPress ① ③ ② ④ accepted args (optional) ① Hook Name ② Callback ④ ③ Priority

accepted_args Number of arguments for the filter

Plugin 4 Figure out what you want to do. I want to add a custom stylesheet

init (action) http://codex.wordpress.org/Plugin_API#Hook_to_WordPress

wp_enqueue_style ① ③ ② ① WordPress function ② Style ID ③ Style URL http://codex.wordpress.org/Function_Reference/wp_enqueue_style

Actions “Do Something” Actions do not need to return anything

Actions Filters 2 Kinds of WordPress Hooks

Actions Actions = “Do Something”

Filters Filters = Transform

Actions and Filters Actions = “Do Something” Filters = Transform

MOAR KITTEHS

Beginning WordPress Plugin Development Aizat Faiz [email_address] http://blog.aizatto.com/?p=3729 kthxbai

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Beginning WordPress Plugin Development

by Aizat Faiz on May 10, 2010

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Beginning WordPress Plugin Development — Presentation Transcript