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This page contains the technical documentation of the WordPress Widgets API (Application Programming Interface). The intended audience for this information includes WordPress theme authors, plug-in authors and anyone who would like to write a stand-alone widget. This document assumes a basic understanding of PHP scripting.
A widget is a PHP object that echoes string data to STDOUT when its widget() method is called.
The WordPress Widget API is located in wp-includes/widgets.php.
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The functions listed below are used to add functioning sidebars to a theme.
register_sidebars( $count, $args );
Registers one or more sidebars to be used in the current theme. Many themes have only one sidebar. For this reason, the count parameter is optional and defaults to one.
The $args parameter will be passed to register_sidebar() and follows its format, with the exception of the name, which is treated with sprintf() to insert or append a unique number to each sidebar if count is plural.
For example, the following line will create sidebars name "Foobar 1" and "Foobar 2":
register_sidebars(2, array('name'=>'Foobar %d'));
register_sidebar( $args );
The optional $args parameter is an associative array that will be passed as a first argument to every active widget callback. (If a string is passed instead of an array, it will be passed through parse_str() to generate an associative array.) The basic use for these arguments is to pass theme-specific HTML tags to wrap the widget and its title. Here are the default values:
'before_widget' => '<li id="%1$s" class="widget %2$s">', 'after_widget' => "</li>n", 'before_title' => '<h2 class="widgettitle">', 'after_title' => "</h2>n"
There are times you might need to call this function instead of register_sidebars. An example of this would be when you want to give unique names to the sidebars, such as "Right Sidebar" and "Left Sidebar", or when they should be marked up differently. The names appear in the admin interface and are used as an index for saving sidebar arrangement. Please note: sidebar arrangements can be reused and overwritten when another theme is chosen that uses the same sidebar names.
The default before/after values are intended for themes that generate a sidebar marked up as a list with "h2" titles. This is the recommended convention for themes. Themes built using this structure can simply register sidebars without issues in regard to the before/after tags. If a theme cannot be marked up in this way, these tags must be specified when registering sidebars. It is recommended to copy the id and class attributes verbatim so that an internal sprintf call can work and CSS styles can be applied to individual widgets.
dynamic_sidebar( $sidebar );
This function calls each of the active widget callbacks in order, which prints the markup for the sidebar. If you have more than one sidebar, you should give this function the name or number of the sidebar you want to print. This function returns true on success, false on failure.
The return value should be used to determine whether to display a static sidebar. This ensures your theme will look good when the Widgets plug-in is not active. Along with a sanity test to prevent fatal errors, below is the recommended use of this function:
<ul id="sidebar">
<?php if ( !dynamic_sidebar() ) : ?>
<li>{static sidebar item 1}</li>
<li>{static sidebar item 2}</li>
<?php endif; ?>
</ul>
If your sidebars were registered by number, they should be retrieved by number. If they had names when you registered them, you will use their assigned names to retrieve them.
To create a widget, you only need to extend the standard WP_Widget class and some of its functions.
That base class also contains information about the functions that must be extended to get a working widget.
The WP_Widget class is located in wp-includes/widgets.php.
You can access the code for widget creation on Github, here. This code also offers a quick widget creation function that you may find useful.
class My_Widget extends WP_Widget {
function My_Widget() {
// widget actual processes
}
function form($instance) {
// outputs the options form on admin
}
function update($new_instance, $old_instance) {
// processes widget options to be saved
}
function widget($args, $instance) {
// outputs the content of the widget
}
}
register_widget('My_Widget');
This sample code creates a Widget named Foo_Widget that has a settings form to change the display title.
/**
* Foo_Widget Class
*/
class Foo_Widget extends WP_Widget {
/** constructor */
function __construct() {
parent::WP_Widget( /* Base ID */'foo_widget', /* Name */'Foo_Widget', array( 'description' => 'A Foo Widget' ) );
}
/** @see WP_Widget::widget */
function widget( $args, $instance ) {
extract( $args );
$title = apply_filters( 'widget_title', $instance['title'] );
echo $before_widget;
if ( !empty( $title ) ) { echo $before_title . $title . $after_title; } ?>
Hello, World!
<?php echo $after_widget;
}
/** @see WP_Widget::update */
function update( $new_instance, $old_instance ) {
$instance = $old_instance;
$instance['title'] = strip_tags($new_instance['title']);
return $instance;
}
/** @see WP_Widget::form */
function form( $instance ) {
if ( $instance ) {
$title = esc_attr( $instance[ 'title' ] );
}
else {
$title = __( 'New title', 'text_domain' );
}
?>
<p>
<label for="<?php echo $this->get_field_id('title'); ?>"><?php _e('Title:'); ?></label>
<input class="widefat" id="<?php echo $this->get_field_id('title'); ?>" name="<?php echo $this->get_field_name('title'); ?>" type="text" value="<?php echo $title; ?>" />
</p>
<?php
}
} // class Foo_Widget
This sample widget can then be registered in the widgets_init hook:
// register Foo_Widget widget
add_action( 'widgets_init', create_function( '', 'register_widget("foo_widget");' ) );
If you use PHP 5.3. with namespaces you should call the constructor directly as in the following example:
namespace a\b\c;
class My_Widget_Class extends WP_Widget {
function __construct()
{
parent::__construct('name1', 'name2');
}
// ... rest of functions
}
and call the register widget with:
add_action('widgets_init',function(){
return register_widget('a\b\c\My_Widget_Class');
});
(see: http://stackoverflow.com/questions/5247302/php-namespace-5-3-and-wordpress-widget/5247436#5247436)
That's all. You will automatically get a multi-widget. No special tweaks needed any longer for that.
More information is available in the version 2.8 information.
