掛勾Hooks(動作Actions and 過濾器Filters), 短碼Shortcodes, and 小工具Widgets

WordPress功能開發(外掛、主題、短碼、小工具)透過核心定義的各種hooks在適當的程式位置與時機加入或擴充功能，hooks分為動作與過濾器，動作掛勾(acion hook)的主要目的是在一個特定的程式動作發時執行客制的功能，而過濾器掛勾則是過濾出特定的內容後進行客制修改，也就是可以任意變更WordPress的輸出內容，例如一篇文章可以加上/變更/去除一段特定的文字或格式…。

Actions

A WordPress action refers to a specific activity that is going to happen at a particular time. With actions, you can add or change the functionality of your plugin. The functions that are attached to an action will be executed once that action is triggered. An example of a WordPress action is save_post. Actions are defined by the do_action function. They require the $tag parameter (the name of the action), and in some cases $args (additional arguments expanding what the action does). WordPress core comes with dozens of predefined actions. However, you can also create your own. Either way, when developing your WordPress plugin, you’ll use do_action to set values for your hooked function. The add_action function will then be used to connect that function up to a specific action.

Filters

WordPress filters are hooks that accept a single variable or a series of variables, and then sends them back after they’ve been modified. In a nutshell, filters let you change the content that is displayed to users. WordPress filters are created using the apply_filters function, and are defined inside of that function. They require the $tag (the filter name) and $value (the filtered value or variable) arguments, with the option of using $var for extra function values. You can create your own filter by using the apply_filters hook. Then to execute it, you can use the add_filter function. This will let you hook a specific function to the filter, so you can manipulate the variable and return it.

Shortcodes

Put simply, shortcodes are user-facing bits of code that give users a quick and easy way to create and display custom functionality to their sites’ visitors. Shortcodes can be placed in posts and pages via the editor, in menus and widgets, and so on. Many plugins make use of shortcodes. You can create your own shortcode by using the add_shortcode function. The name of your shortcode will be the first variable, and the second variable will be the output function. The output function consists of three values: attributes, content, and name.

Widgets

Another way to enable plugin functionality through a simple interface is by using WordPress widgets. You can create a widget by extending the WP_Widget class. WordPress uses an object-oriented design approach to widgets, meaning that the functions and values are stored in the single entity of a class. Before you begin your WordPress plugin development, we recommend reading up on these topics to further understand how plugins work. Here are some helpful WordPress plugin development tools and resources you can use:

• WordPress的Hook機制與原理
• WordPress Code Reference
• WordPress Codex: Writing a Plugin
• WordPress Developer Plugin Handbook