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Backward compatibility issues

From: WordPress: Creating Custom Widgets and Plugins with PHP

Video: Backward compatibility issues

WordPress has been through many iterations. There have been a number of different versions. Interestingly enough, they all have code names of jazz musicians, like version 2.7 was code named John Coltrane, and the most recent 3.0 was code named Thelonious Monk. What's great about having these different versions is over the time WordPress contributors are constantly making this a better and better environment to work with. However, because there are always changes to this environment, it's really important that we pay attention to the API and do some certain practices that make sure that we can account for these different versions.

Backward compatibility issues

WordPress has been through many iterations. There have been a number of different versions. Interestingly enough, they all have code names of jazz musicians, like version 2.7 was code named John Coltrane, and the most recent 3.0 was code named Thelonious Monk. What's great about having these different versions is over the time WordPress contributors are constantly making this a better and better environment to work with. However, because there are always changes to this environment, it's really important that we pay attention to the API and do some certain practices that make sure that we can account for these different versions.

If you go to the WordPress web site, there's a page dedicated specifically to WordPress versions. You can see when the versions were released, and you can read change logs for each of them. Note you can also see their code names. There have been quite a number of versions, and as they go from version to version, they can change the structure of the database. They can change the functions that exist, actions and hooks changes, and there can be all kinds of changes in the user interface. So there are a few things that can go wrong with our code because of this.

One is an old version of WordPress can break when they install your plugin because your plugin doesn't work. Remember, every time you have a plugin, it gets included in every request, which means that code is always going to execute. So if there's a problem in that code, it's literally going to hold production and throw an error. Another thing that can happen is a new version of WordPress is installed, and it breaks because your plugin doesn't have compatibility. It's extremely difficult, and a lot of it is just keeping up with the API, but there are a few things that you can know about.

One is there's a special page dedicated to deprecated functions. These are functions that no longer exist or are no longer popularly used in the WordPress system. If you need to use them, they're located in a number of different files, and this page will tell you where to find them. You can always include them in your script, if it's necessary, and you don't want to rewrite your code. However, it's best to use whatever they are replaced with, and usually there will be some new solution. Another way to get around this is to use the function exists function, to test and see if functions are there.

Let's go into our cc_comment plugin that we worked on earlier. One of the things that we did recently was we registered an uninstall hook. Well, this particular function register_uninstall_hook didn't exist until WordPress 2.7. So if you try to run this in a previous version, it would actually throw an error. We don't have to worry about adding actions and filters. If you try and add an action to a filter that doesn't exist in a version of WordPress that they're running, it'll basically just get ignored.

However, because this is a function that's actually being executed, it will throw an error. So what you want to do in instances like this, if you know you're going to run a function that may not work with the version of WordPress someone's using, you simply wrap it in if function_exists, and then just put the name of the function: register_uninstall_hook. If that exists then it will execute whatever is in this code block, in which case it'll run that function; otherwise it won't happen, which means they won't be able to uninstall prior to 2.7, but that's okay, because it wouldn't have worked.

So long story short, keeping track of WordPress versions becomes of utmost importance as a plugin developer, so you know what exists and what doesn't. The good news is that the Codex provide a lot of information about functions, their availability, and what version they do and don't exist in. The bad news is it's all up to you.

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Image for WordPress: Creating Custom Widgets and Plugins with PHP
 
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  1. 1m 49s
    1. Welcome
      1m 16s
    2. Using the exercise files
      33s
  2. 23m 29s
    1. WordPress overview
      2m 32s
    2. Installing WPI for Windows
      3m 42s
    3. Installing MAMP for the Mac
      3m 25s
    4. Installing and configuring WordPress
      5m 51s
    5. Comparing WordPress 3.0 with previous versions
      2m 57s
    6. Setting up a PHP/WordPress development environment
      5m 2s
  3. 14m 47s
    1. Exploring WordPress plugins
      3m 42s
    2. Administering plugins from the WordPress admin
      5m 23s
    3. Exploring where plugins reside
      2m 51s
    4. Introduction to hooks
      2m 51s
  4. 39m 28s
    1. Creating the plugin PHP file(s)
      3m 12s
    2. More on hooks: Actions and filters
      3m 15s
    3. Installation and activation
      4m 6s
    4. Writing activation code
      3m 45s
    5. Writing an action
      5m 12s
    6. Writing a filter
      4m 15s
    7. About pluggable functions
      2m 1s
    8. Writing a pluggable function
      5m 30s
    9. Using template tags
      2m 46s
    10. Introducing shortcode
      5m 26s
  5. 26m 2s
    1. Widgets and the WordPress Widgets SubPanel
      2m 54s
    2. Comparing widgets and plugins
      1m 8s
    3. Using and customizing built-in widgets
      3m 18s
    4. Creating a new widget
      7m 21s
    5. Writing the constructor and registering widgets
      5m 20s
    6. Enabling configuration of widgets
      6m 1s
  6. 44m 59s
    1. Creating an admin interface
      5m 25s
    2. Saving data to the database
      5m 39s
    3. Securing form submission with nonces
      2m 25s
    4. Options editing post-WordPress 2.7
      4m 8s
    5. Integrating with the WordPress admin menus
      3m 34s
    6. WordPress admin dashboard API
      4m 5s
    7. Using existing options and option editing pages in WordPress
      5m 19s
    8. Using jQuery and AJAX for administration
      14m 24s
  7. 27m 13s
    1. Accessing the WordPress database
      5m 45s
    2. Using the built-in schema
      2m 21s
    3. Accessing data using $wpdb
      5m 15s
    4. Creating new tables
      7m 18s
    5. Inserting data
      6m 34s
  8. 26m 27s
    1. Introducing the Loop
      6m 22s
    2. Using WP_Query()
      3m 11s
    3. Custom filtering and sticky posts
      4m 58s
    4. Using jQuery and AJAX for posts and pages
      11m 56s
  9. 12m 9s
    1. Registering and promoting plugins
      2m 28s
    2. Creating an uninstall function
      5m 53s
    3. Backward compatibility issues
      3m 48s
  10. 15m 3s
    1. Understanding security issues
      11m 20s
    2. Internationalizing your plugin
      3m 43s
  11. 18s
    1. Goodbye
      18s

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