Managing Plugins
After you install a plugin in WordPress, you can manage it, along with all other plugins, on the Plugins ➪ Installed Plugins screen. Here you can find a list of all plugins, active or not, available in your WordPress installation. You can easily activate, deactivate, edit, update, and delete plugins from this screen.
The Plugin screen also features bulk actions for activating, deactivating, updating, and deleting plugins. Check all the plugins you want to manage and then select the appropriate bulk action from the drop‐down menu. This process makes managing multiple plugins a breeze!
Editing Plugins
WordPress features a built‐in plugin editor on the Plugins ➪ Plugin Editor screen. The plugin editor enables you to view and edit the source code of any plugin installed in WordPress. Keep in mind you can edit the source code only if the plugin file is writable by the web server; otherwise, you can only view the code.
To use the editor, select the plugin from the drop‐down menu on the top‐right portion of the Edit Plugins page. The editor lists all files associated with the selected plugin. There is also a documentation lookup feature that makes it easy to research a specific function's purpose in the plugin you are reviewing.
WARNING A word of caution when using the built‐in plugin editor: a browser doesn't have an Undo button. There is also no code revision history, so one bad code edit can crash your entire website with no way to revert the changes. It's best to use the code editor for reference only and never use it to edit your plugin files.
Plugin Directories
A lesser known fact is that WordPress actually features two plugin directories. The primary directory is located at wp‐content/plugins in a standard WordPress installation. The second, lesser known plugin directory is at wp‐content/mu‐plugins. The mu‐plugins directory, which stands for Must‐Use, is not automatically created by WordPress, so it must be manually created to be used.
The primary difference between the two is that the mu‐plugins directory is for plugins that are always executed. This means any plugin included in this directory will automatically be loaded in WordPress and across all sites in the network if you run Multisite. Mu‐plugins are always on and cannot be deactivated.
NOTE The mu‐plugins directory will not read plugins in a subfolder, so all plugins must be individual files or must include additional files that exist in a subdirectory. Any plugin files in a subfolder will be ignored unless included in the primary plugin file.
Types of Plugins
WordPress features a few different types and statuses for plugins, as shown in Figure 1‐4. You need to understand the difference when administering and creating plugins for WordPress.
FIGURE 1‐4: Types and statuses for plugins
Active: Plugin is active and running in WordPress.
Inactive: Plugin is installed but not active. No code from the plugin is executed.
Recently Active: A temporary status given to any plugin that has been recently deactivated.
Must‐Use: All plugins installed in the wp‐content/mu‐plugins directory. All Must‐Use, or MU, plugins are loaded automatically. The only way to deactivate an MU plugin is to remove it completely from the directory.
Drop‐ins: Core functionality of WordPress can be replaced by Drop‐in plugins. These plugins are specifically named PHP files located in the wp‐content directory. If WordPress detects one of these files, it will be automatically loaded and listed under the Drop‐in filter on the Plugin screen. Currently ten Drop‐in plugins are available.advanced‐cache.php: Advanced caching plugindb.php: Custom database classdb‐error.php: Custom database error messageinstall.php: Custom installation scriptmaintenance.php: Custom maintenance messageobject‐cache.php: External object cachesunrise.php: Advanced domain mappingblog‐deleted.php: Custom blog deleted messageblog‐inactive.php: Custom blog inactive messageblog‐suspended.php: Custom blog suspended message
The last four Drop‐in plugins are specific to the WordPress Multisite feature. A standard WordPress installation will have no use for these plugins.
When developing a new plugin, determine what type of plugin you want to create before you start the development process. Most plugins will be standard WordPress plugins, but occasionally you might need to create a Must‐Use or Drop‐in plugin.
SUMMARY
In this chapter, you learned about plugins and how they can interact with WordPress using the available APIs. The major advantages to using plugins and why plugin functionality shouldn't always be included in a theme were discussed. Installing and managing plugins in the WordPress Dashboard was covered.
Now that you understand how plugins work in WordPress, it's time to create the plugin foundation!
2 Plugin Framework
WHAT'S IN THIS CHAPTER?
Creating a solid plugin foundation
Determining directory and URL paths
Creating activation and deactivation functions
Cleaning up during the uninstall process
Writing code following coding standards
Properly documenting plugin code
CODE DOWNLOADS FOR THIS CHAPTER
The code downloads for this chapter are found at www.wiley.com/go/prowordpressdev2e on the Downloads tab.
When creating a plugin for WordPress, it's important to start with a solid foundation. This means getting your plugin folders and files organized and coming up with a naming scheme that you can use consistently throughout the plugin. The setup is the most essential piece of the puzzle. By nailing down these basics, you'll be well on your way to building your first WordPress plugin.
REQUIREMENTS FOR PLUGINS
The WordPress plugin system is flexible and allows for plugins to be either a single file or a folder with many files. In this section, you'll learn the basics of creating a plugin.
Naming Your Plugin
The most
