Key Takeaways
- WordPress plugins, which extend the functionality of the blogging software, can be created by users when they can’t find an existing plugin that meets their needs. The creation process involves creating a new subdirectory in the wp-content/plugins directory and providing a descriptor in the PHP file comments to identify the plugin.
- WordPress provides a WP_Widget class that can be extended to create custom widgets. The WP_Widget class has four methods that should be overridden: __construct(), form(), update(), and widget(). These methods initialize the widget, display a form for customization, update widget properties, and display the widget on the blog, respectively.
- When creating a WordPress plugin, it’s important to follow best practices such as using proper naming conventions, ensuring security by validating and sanitizing user input, and making the plugin translatable to reach a wider audience. Compatibility with all themes can be achieved by adhering to WordPress coding standards and testing the plugin with different themes.
- Debugging a WordPress plugin involves using the built-in debugging system or a PHP IDE with a debugger. Ensuring the plugin’s security involves validating and sanitizing user input, using nonces to verify request sources, setting proper file permissions, and using WordPress API functions for data manipulation. Regular updates and testing can help identify potential security vulnerabilities.
The Main Plugin File
Plugins are detected automatically from the wp-content/plugins directory within your WordPress installation directory. When creating a new plugin, you should create a new subdirectory there. The name of the subdirectory can be anything you want; a sensible option would be to call it the name of your plugin. Try to avoid generic names such as “textwidget” or “shoppingcart” as this may have already been used with another plugin and will cause problems should you wish to distribute it to other users of WordPress. For this example, create a subdirectory named phpmaster_examplewidget. WordPress detects that a plugin is available from a descriptor placed in the comments of a PHP file. The descriptor must provide the basic information about what the plugin does, who created it, and its license information. This is what WordPress uses to identify that a plugin is present and ready to be activated. This example plugin will contain the definition at the top a file placed in your newly created phpmaster_examplewidget directory. The name of the file is also arbitrary but it’s advisable to provide a meaning name. This example will call the file widget_init.php.<span><span><?php </span></span><span><span>/* </span></span><span><span>Plugin Name: Simple Text Plugin </span></span><span><span>Plugin URI: http://www.example.com/textwidget </span></span><span><span>Description: An example plugin to demonstrate the basics of putting together a plugin in WordPress </span></span><span><span>Version: 0.1 </span></span><span><span>Author: Tim Smith </span></span><span><span>Author URI: http://www.example.com </span></span><span><span>License: GPL2 </span></span><span><span> </span></span><span><span> Copyright 2011 Tim Smith </span></span><span><span> </span></span><span><span> This program is free software; you can redistribute it and/or </span></span><span><span> modify it under the terms of the GNU General Public License, </span></span><span><span> version 2, as published by the Free Software Foundation. </span></span><span><span> </span></span><span><span> This program is distributed in the hope that it will be useful, </span></span><span><span> but WITHOUT ANY WARRANTY; without even the implied warranty of </span></span><span><span> MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the </span></span><span><span> GNU General Public License for more details. </span></span><span><span> </span></span><span><span> You should have received a copy of the GNU General Public License </span></span><span><span> along with this program; if not, write to the Free Software </span></span><span><span> Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA </span></span><span><span> 02110-1301 USA </span></span><span><span>*/</span></span>This is the required structure for any plugin you’ll create for WordPress. Now when you log in and look at the plugin administration screen in WordPress you’ll see the new plugin is ready for activation.
WordPress Widgets
WordPress provides a class which you can extend named WP_Widget. When you extend it, your own widget will be available to any sidebar that your theme offers. WordPress ships with a number of default widgets such as “Recent Posts” and “Archives” which extend WP_Widget. The WP_Widget class provides four methods which should be overridden:- __construct() – call the parent constructor and initialize any class variables
- form() – display a form for the widget in the admin view to customize the widget’s properties
- update() – update the widget’s properties specified in the form in the admin view
- widget() – display the widget on the blog
The Constructor
The constructor is like any other constructor you’ve probably written. The important thing to remember here is to call the parent constructor which can take three arguments: an identifier for the widget, the friendly name of the widget (this will appear as the title of the widget in the admin widget screen), and an array detailing the properties of the widget (which only needs a “description” value).<span><span><?php </span></span><span><span>/* </span></span><span><span>Plugin Name: Simple Text Plugin </span></span><span><span>Plugin URI: http://www.example.com/textwidget </span></span><span><span>Description: An example plugin to demonstrate the basics of putting together a plugin in WordPress </span></span><span><span>Version: 0.1 </span></span><span><span>Author: Tim Smith </span></span><span><span>Author URI: http://www.example.com </span></span><span><span>License: GPL2 </span></span><span><span> </span></span><span><span> Copyright 2011 Tim Smith </span></span><span><span> </span></span><span><span> This program is free software; you can redistribute it and/or </span></span><span><span> modify it under the terms of the GNU General Public License, </span></span><span><span> version 2, as published by the Free Software Foundation. </span></span><span><span> </span></span><span><span> This program is distributed in the hope that it will be useful, </span></span><span><span> but WITHOUT ANY WARRANTY; without even the implied warranty of </span></span><span><span> MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the </span></span><span><span> GNU General Public License for more details. </span></span><span><span> </span></span><span><span> You should have received a copy of the GNU General Public License </span></span><span><span> along with this program; if not, write to the Free Software </span></span><span><span> Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA </span></span><span><span> 02110-1301 USA </span></span><span><span>*/</span></span>With the basic widget structure in place, you’ll want to register the widget and make sure this is done at a time when all the other widgets are being initialized. Registering a widget is done through the register_widget() function which takes a single argument, the name of the class which extends WP_Widget. This call to register the widget must be called at an appropriate time, so the particular WordPress hook you’ll want to use is called “widgets_init”. To associate registering the widget with the hook, you use add_action() which takes the name of the hook as the first argument and a function to execute as the second. (The second argument can either be the string name of a function or closure.) This code should go directly under the descriptor of the plugin that was created in widget_init.php.
<span><span><?php
</span></span><span><span>class TextWidget extends WP_Widget
</span></span><span><span>{
</span></span><span> <span>public function __construct() {
</span></span><span> <span><span>parent::</span>__construct("text_widget", "Simple Text Widget",
</span></span><span> <span>array("description" => "A simple widget to show how WP Plugins work"));
</span></span><span> <span>}
</span></span><span><span>}</span></span>
Now that it has been registered and initialized, you’ll be able to see your widget available for use.
The form() method
The example widget here should let you enter a title and some text to be displayed when viewed on the blog, so in order to be able to amend these two aspects of the widget you need to create a form to prompt for these values. The form() method is used in the widget administration screen to display fields which you can later use to alter the functionality of the widget on the site itself. The method takes one argument, an $instance array of variables associated with the widget. When the form is submitted, the widget will call the update() method which allows you to update the fields in $instance with new values. Later, widget() will be called and will make use of $instance to display the values.<span><span><?php
</span></span><span><span>add_action("widgets_init",
</span></span><span> <span>function () { register_widget("TextWidget"); });
</span></span><span><span>?></span></span>
You use WP_Widget‘s get_field_id() method and get_field_name() method to create IDs and names for the form fields respectively. WordPress will generate unique identifiers for you so as not to clash with other widgets in use, and when the form is submitted the values will update the relevant $instance array items. You can use the passed $instance argument to populate the form fields with values should they already be set.
This is what the form looks like in the admin view:
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