A peek into the world of WordPress plugin development

r3df.com
Rick Radko
“A Peek into the World of
WordPress Plugin
Development”
WordCamp Toronto
October 5th, 2013
Slides: http://www.slideshare.net/r3df

© 2013 Rick Radko, r3df.com
A little bit about me
Rick Radko – R-Cubed Design Forge
 Software, web and app designer/developer.
 Creating web sites since 1996.
 WordPress enthusiast.
 Co-organizer of WordCamp Ottawa 2013 & 2014
 Co-organizer of: The Ottawa WordPress Group.
http://wpottawa.org
Slides are posted at:
 http://www.slideshare.net/r3df
1

About this presentation
In this presentation I will run through the
construction of a simple plugin.
 The example I will use is a plugin I have published on
wordpress.org.
 The intent of this session is
exposure to concepts and
ideas, not complete
understanding.
- No instant code ninjas!
 There is tons of material on
the net, in books and other
resources to learn more at a
more leisurely pace.
2Image Credit: Derivative of CC Image by Dani Latorre on Flickr

What is a plugin?
Plugins are blocks of code added to WordPress to
extend, or change the functionality of:
 WordPress
 Other plugins
 Themes
You can create a custom plugin to do just about
anything you want.
 1000's of plugins available to add to your site.
3

This is a plugin
4

More about plugins…
WordPress plugins:
 Are written in PHP. (That gobbledygook on the
previous slide was PHP.)
 Can be a couple lines of code.
 Or 60,000 lines of code.
PHP Help:
 Online PHP Manual:
www.php.net/manual/en/index.php
 W3schools: www.w3schools.com/php/default.asp
 + Google of course…
5

Plugins also:
WordPress plugins also:
 Make use of WordPress API‟s.
 The Codex - learn about all things WordPress
 codex.wordpress.org/Writing_a_Plugin
 Will likely have some HTML and CSS.
 www.w3schools.com + many other resources.
 May access the database (MySQL).
 www.mysql.com + many other resources.
 May use some JavaScript.
 www.w3schools.com again + many other resources.
6

Tools to use for programming
Programming editors:
 Code completion
 Syntax highlighting
 Bracket matching
 “Light” and fast
7
 Windows: Notepad++, Sublime Text $$
 Mac: TextWrangler, Coda $$, Sublime Text $$

More tools
IDE – Integrated Development Environment
 NetBeans, Eclipse, Aptana, PhpStorm $,
Komodo $, + more
 Do a lot more than a programming editor
 “Heavier”
Jeremy Clarke - WordCamp Montreal: Code Faster
and Smarter PHP with IDE‟s Like NetBeans
8

A place to work
Development “Dev” site:
 Safe place to work that won‟t disturb a live site.
 Does not matter if you WSOD the site.
 2 Common options:
 Sub-domain on your hosted site.
 “Local” web server on your pc/laptop.
Requires some set-up – lots of tutorials on net.
No internet connection needed.
Fast, no internet lag, no FTP.
BitNami, XAMPP, Wamp, Mamp.
9

The header – the only required part of a plugin
10
Plugin header details:
codex.wordpress.org/Writing_a_Plugin#File_Headers
Creates this plugin information on the Plugins page in the Dashboard

Where do we put the header?
Simplest plugin is a file only:
 site-plugin.php
 in the WordPress plugins folder: wp-content/plugins/
11

Better plugin structure
A better structure for your plugin: folder + file
12

Empty plugin template
We now have an empty plugin that could be used
as a template to:
 Make your own plugin. (a blank template)
 Change the file name, folder name and the header
info: name, description, author, etc.
 Make a “Site Plugin” to add code to run on your
site that is often put into functions.php. See:
Don‟t: “Just paste this code in your functions.php”
or
ottopress.com/2011/creating-a-site-specific-
snippets-plugin/
13

Meetup widget on wordpress.org
14
wordpress.org/extend/plugins/r3df-meetup-widget

Edit the site-plugin template
Revised plugin header:
15

Change the file names
Name the file: r3df-meetup-widget.php
And the folder: r3df-meetup-widget
16

WordPress widget outline
Basic widget outline:
codex.wordpress.org/Widgets_API
17

Lets add a widget!
We add this code to the plugin:
 The "class" creates a new object that lets us
“extend” the WordPress WP_Widget class.
 The WP_Widget class does all the heavy lifting in
creating a widget.
 Use the codex example, change the class name.
Codex: codex.wordpress.org/Widgets_API
API – Application Programming Interface
18

Getting into the “action”
 Tells WordPress to register our widget at the time
it is setting up widgets - 'widgets_init'.
 When you create a widget, the only thing you need
to change in the action is the widget name.
Actions are very important to WordPress plugins.
19

WordPress actions
Actions are one of 2 types of WordPress “Hooks”.
 Specific events (100‟s) trigger them, for example:
 Publishing a post or page
 Displaying a post, page or admin page.
 Displaying a menu.
 Displaying the page content.
 codex.wordpress.org/Plugin_API/Action_Reference
 To use an action, your plugin defines a function for
WordPress to execute at that action event.
 Generally actions “do” things.
 Filters, which we will see later “change” things
20

Getting hooked on actions
WP Native Dashboard Fix
 Moving the menu item was accomplished by hooking
into the action „admin_bar_menu‟.
 10 lines of code and you have a maintainable fix
instead of hacked plugin.
21

The widget “constructor function”
Add the constructor function:
 Sets up the widget with an id, name and description.
 Note: the name and description have been internationalized
 __( ) is a function to assist in showing other languages
 codex.wordpress.org/I18n_for_WordPress_Developers
 Just change the ID the description and the name to
reuse this block of code from the codex. 22

The widget function
Add the widget function:
 The <a … /a> part is the content we want to show, the rest is
required for a standard widget.
 The extract($args) expands an array (group) of variables into
individual variables: $before_widget, $after_widget,
$before_title, $after_title.
23

Filtering the title
 The filter lets other plugins or code, add functions
to change the title content.
 It‟s important to have this code in the widget.
 If a theme were to rely on this filter to affect the way
widget titles are shown, the site wouldn‟t render
correctly without it.
24

Filters
“Filters” are the other “hook” type in WordPress.
Like actions:
 Specific events (100‟s) trigger them.
 codex.wordpress.org/Plugin_API/Filter_Reference
 Your plugin defines a function for WordPress to
execute at the time of the trigger.
Unlike actions:
 Filters change things, content passes through a
filter function and must be returned, either
updated/altered or unchanged.
25

The form function
Add the form function:
 This function creates the widget box you see in your
dashboard in admin.
 The <p … /p> part defines the HTML for your fields in
the admin widget. These can be copied from
examples.
26

The update function
Add the update function:
 This function saves the option data from the
widget box you see in admin.
 It also is used to “clean” input that is provided.
 strip_tags removes HTML and PHP from the title.
27

The plugin code
28

The plugin code continued…
29

Activation error
 Debugging errors can be tricky, the line indicated for
the error may be misleading, the error could be one or
more lines above.
30

The resulting widget on the site
You now have a Meetup widget.
 But it's not yet quite what we were expecting…
31

We have a widget that works, but…
Our widget plugin:
 has all the required elements for a widget.
 could build used as a base to create new widgets.
But, it‟s not a great plugin:
 You need to edit the code to change the URL or
the displayed text.
 It‟s not very nice looking.
 We need to add an image for the logo and CSS.
 It would not be very good to give to other users.
This starts to make things a bit more complicated.
32

Lets add the options to admin
This is what we want to get to:
 A box for text to
display so you can
choose what is shown
for the link text.
 A box for the URL we
want.
 And in the final
version on .org there
is also a selector to
adjust the text
position. 33

Update the form function
 The first 4 lines get the current saved value for
each setting to a variable that is used in the form
sections.
 The next 4 blocks of code starting with <p> each
represent the html for the form item for each
setting.
34

The first 3 blocks of code
 The code is similar and repetitive.
35

The last block of code
 A lot of this code can be copied from examples
and then modified to suit your plugin.
 Look at other plugins in the repository.
 Check for examples in the codex.
36

Add the new options to the update function
The update function for all of the added options.
 The wp_parse_args sets defaults for values that
don't exist in the input value array.
 In this case the array in $new_instance.
37

Update the widget to use the new options
38

The extended output block
The content area has been changed:
 to allow for CSS styling,
 to add the image,
 To add the option „middle‟ for single line display.
39

Load a css file
 Added section in the constructor to load css.
40

Add style function
 This function has been added after the update
function.
 It loads a CSS file "the WordPress way"
 codex.wordpress.org/Function_Reference/wp_enqueue_style
NOTE: There is a similar process for loading scripts.
 codex.wordpress.org/Function_Reference/wp_enqueue_script
41

The added style sheet
The link to load
this CSS style
sheet is added into
the web page
header.
42

Wrapping up the plugin…
We need 2 more additions to the plugin to round it
out for public use:
 A function to take care of loading the text domain.
 Needed to enable the display of translated text for
the plugin.
 A function to clean up on uninstall.
43

Text domain
 A function to load the text domain:
 The action to call it in the constructor:
44

And finally: uninstall.php
This added file runs if the plugin is uninstalled.
 It removes the settings that were saved in the
database for the widget.
 Plugins should clean up after themselves.
45

The files now in the plugin
 The CSS is in the /inc folder.
 The /lang folder is for translations of the plugin.
 readme .txt & screenshots are needed for the
repository.
46

The new widget
Once you‟ve hit save, take a look at your site:
 That‟s more like it!
47

Other possible plugin functions
Plugins can have:
 activation/deactivation routines
 menu items
 options pages
48

What next?
 Read some books
 Watch some WordCamp talks – next couple of
slides.
 Read the codex:
 http://codex.wordpress.org/Writing_a_Plugin
 http://codex.wordpress.org/Plugin_Resources
 http://codex.wordpress.org/Developer_Documentation
Try some experements.
49

WordPress plugin books 1
Professional WordPress Plugin
Development
by: Brad Williams, Ozh Richard, Justin
Tadlock
Related WordCamp Presentations:
 http://www.slideshare.net/williams
ba/create-your-first-wordpress-
plugin
50

WordPress Plugin Development
Cookbook
by: Yannick Lefebvre
Related WordCamp videos:
 http://wordpress.tv/2011/08/16
/yannick-lefebvre-plugin-
development-demystified/
 http://wordpress.tv/2012/09/10
/yannick-lefebvre-wordpress-
plugin-development-201/
51

WordPress 3 Plugin Development
Essentials
by: Brian Bondari, Everett Griffiths
52

PHP books 1
Programming PHP
by: Kevin Tatroe, Peter MacIntyre,
Rasmus Lerdorf
53

PHP books 2
Learning PHP, MySQL,
JavaScript, and CSS
by: Robin Nixon
54

Contact
Rick Radko
 email: wpinfo@r3df.com
 twitter: @r3designforge
Slides at:
 www.slideshare.net/r3df
55

A peek into the world of WordPress plugin development

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