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How do WordPress themes work?

From: WordPress: Building Themes from Scratch Using Underscores

Video: How do WordPress themes work?

When you create a WordPress theme, it's Once you have the ID, it's sent to the database,

How do WordPress themes work?

When you create a WordPress theme, it's important to understand how a theme actually works. Rather than provide a single template for each individual scenario, WordPress uses a distributed templating system based on dry-development principles. To make sense of all this, let's first look at what happens when you enter an address to a WordPress post into your browser. So let's assume your WordPress site is set up with custom permalinks, so they have these nice, human-readable permalinks like mor10.com/test-drive.

The first thing that happens here is WordPress will translate that human-readable permalink into a machine-readible permalink. And you end up with mor10.com/?p=2726. And this last component here, p equals 2726, is what's important, because each entry in WordPress, whether it be a post, a page, a category, a menu item, or anything else, has a custom ID that you can target when you want to bring it into your page. Once you have the ID, it's sent to the database, and the database immediately checks what kind of content is this.

In the case of 2726, it's a post, and this information is sent back to the file server and the correct template is retrieved. For a post, that template is single.php, and you'd think that single.php would contain all the necessary code to display all the content, but that's not the case. In WordPress we have a distributed system, so single.php sets up the scaffolding for the post, and then calls in a bunch of other template files. So the content may be displayed by content.php or content-single.php.

The header is displayed by header.php, the sidebar by sidebar.php, and the footer by footer.php. And this means we can easily swap out one or all of these components without having to worry about any of the other ones. You can see the value of this when you then go to an index.php template. So this will be the front page, or any of the other blog index pages. Here we're using the same header.php, the same sidebar.php, and the same footer.php to display the overall content around.

But since we are now showing an index and we have to loop through multiple different posts, we keep running content.php over and over again, one time for each post. And that way we're reusing the same file over and over again instead of repeating the same code in the same template multiple different times. But WordPress is not just restricted to just posts. You also have pages and pages, like posts, have ID numbers. When you find a page you can then also apply a custom page template to that page, so pages can be displayed completely differently from other content.

You could, for example, choose to add a custom header. In that case, the file would be called something like header-custom and you could call it in to display in place of the regular header. You can also choose to display the regular footer, even though you have a custom header. And you could choose to eliminate the sidebar and just display the page content from content-page.php across the width of the entire screen. This distributed structure is what I referred to when I said that WordPress is based on DRY development principles.

DRY is an acronym that stands for Don't Repeat Yourself. And that's a good mantra to follow when you're writing code, because you don't want to repeat the same code over and over. Instead, you want to separate all repeatable elements into either separate files or separate functions, so that if you want to repeat the header in multiple different templates, then you just put it in a header file. If you want to repeat content several times in different templates, or maybe even several times within one template, then you put it in a content file.

If you want a custom header but you still want to be able to display the regular footer, then you split them out, so that you can call one or the other when you want to. And if you have a function within the content template, for instance, displaying the author name and the publishing date, and you know that you'll repeat that, also, in another content template, or somewhere else on the site, then you break that out into a separate function that is then called in and then used whenever necessary. Having a clear understanding of the distributed nature of WordPress themes allows you to quickly identify and navigate between different sections of your theme.

The main thing to remember here is that every major piece of content usually has its own template file. Sidebars are found in sidebar.php, headers in header.php, content in content.php, or a variety of different content files, and so on, and so on.

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This video is part of

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  1. 10m 55s
    1. Welcome
      1m 4s
    2. What to know before you start this course
      2m 40s
    3. How this course and the lesson files work
      3m 12s
    4. Introducing Simone: A preview of the final project
      3m 59s
  2. 21m 28s
    1. Installing and running WordPress on your computer
      3m 53s
    2. Getting and installing Underscores
      4m 11s
    3. Installing WordPress Theme Unit Test data
      4m 18s
    4. Installing the Developer plugin
      2m 58s
    5. Installing and setting up NetBeans or another IDE
      6m 8s
  3. 16m 15s
    1. Designing for mobile, content, and style
      4m 52s
    2. How do WordPress themes work?
      4m 48s
    3. Understanding the WordPress template hierarchy
      2m 19s
    4. Underscores: An overview
      4m 16s
  4. 37m 5s
    1. Setting up style.css
      4m 47s
    2. Configuring baseline settings and functions
      6m 6s
    3. Enabling custom fonts and font icons
      5m 44s
    4. Applying global styles
      5m 11s
    5. Styling basic layout components
      6m 19s
    6. Making the site layout responsive
      8m 58s
  5. 23m 18s
    1. Styling the default header
      6m 25s
    2. Hiding the site title and tagline
      5m 32s
    3. Adding an optional header image function
      5m 23s
    4. Placing the header image behind the site title
      5m 58s
  6. 40m 55s
    1. Setting up menus
      3m 12s
    2. Styling the menu
      7m 42s
    3. Using Superfish for accessible menus
      8m 0s
    4. Making the menu responsive
      7m 3s
    5. Creating a custom social media menu
      5m 51s
    6. Styling the menu with icons from Font Awesome
      9m 7s
  7. 18m 9s
    1. Adding the search form
      6m 27s
    2. Adding the search icon
      6m 55s
    3. Adding show/hide functionality to the search form with jQuery
      4m 47s
  8. 33m 20s
    1. Adding a widgetized area to the footer
      7m 10s
    2. Using the Monster widget plugin to test all widgets
      2m 11s
    3. Styling the footer
      3m 6s
    4. General widget styling
      5m 33s
    5. Adding custom styles to specific widgets
      7m 34s
    6. Using Masonry to make footer widgets responsive
      7m 46s
  9. 54m 49s
    1. Changing the Single Post Template content structure
      5m 54s
    2. Changing the output of meta elements
      7m 2s
    3. Styling the Single Post Template
      7m 57s
    4. Making post meta responsive
      6m 21s
    5. Styling blockquotes
      5m 39s
    6. Creating pull quotes and pull images
      5m 1s
    7. Working with image captions
      4m 27s
    8. Working with image galleries
      4m 57s
    9. Single-post navigation
      7m 31s
  10. 30m 23s
    1. Working with the comments template
      8m 42s
    2. Using Gravatars in comments
      2m 42s
    3. Styling comments
      7m 26s
    4. Highlighting post author comments
      3m 36s
    5. Styling the comment form and messages
      7m 57s
  11. 18m 43s
    1. How do featured images (post thumbnails) work?
      2m 57s
    2. Defining featured image sizes
      3m 30s
    3. Generating new featured images with a plugin
      1m 46s
    4. Adding featured images to a template
      5m 7s
    5. Styling the featured image
      5m 23s
  12. 1h 2m
    1. The index template hierarchy
      2m 21s
    2. Customizing and styling index templates
      10m 10s
    3. Displaying excerpts or full content on index pages
      3m 6s
    4. Adding a custom Read More link
      3m 48s
    5. Adding featured images
      4m 0s
    6. Creating custom pagination navigation
      6m 4s
    7. Highlighting Sticky Posts
      2m 55s
    8. Creating custom post format templates
      5m 30s
    9. Highlighting the most recent post in the index template
      7m 22s
    10. Embracing modular design
      2m 29s
    11. Working with archive.php
      5m 54s
    12. Customizing the search results and the 404 template
      8m 28s
  13. 9m 7s
    1. Styling pages
      3m 4s
    2. Creating custom page templates
      6m 3s
  14. 4m 30s
    1. Adding editor styles to match front-end styles
      4m 30s
  15. 2m 20s
    1. Further learning
      2m 20s

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