Wordpress | Design an entire category (Not category page) - wordpress

Question

I'm creating my first wordpress theme, and I've looked around on google, and the wordpress codex for an answer to my question, but I can't seem to find exactly what I'm looking for, or couldn't get it working.
What I'm trying to do, or trying to figure out, is how I can make it so a certain category has a certain design.
So if I wanted to make an index.php for any music videos in "www.domain.com/music/trash/drake-song.mp4.html"
the trash category, it'd have its own design, but songs in
"www.domain.com/music/good-music/coldplay-viva-la-vida.mp4.html"
the good-music category, I want it to look pretty much completely different. I've tried using something similar inside my header.php to this;
<?php
if( is_tag( 'good-music' ) ):
$my_classes = array( 'good-class', 'good-class-two' );
else:
$my_classes = array( 'not-good-class' );
endif;_
?>
but it seemed to simply change the category page.
"www.domain.com/categories/good-music"
Anyone know what I could be doing wrong? I know basic html/css/php/javascript, new to creating a WordPress theme, and can't seem to get this working..
Also:
Using XAMPP to host locally, using Friendly URL's, properly configured

Answer 1

In order to generate category-specific markup for a single post layout, you can put code like the below in your single.php file after the call of get_header().
Please note that this checks for your category based upon category slug. So if your category slug (the url version of your category) does not match the first arguments in the in_array() function call below, then you should change the argument to match the slug for your category.
<?php
/* Start the Loop */
while ( have_posts() ) : the_post();
?>
<?php
$categories = get_the_category();
$catSlugs = array();
foreach ($categories as $category){
$catSlugs[] = $category->slug;
}
if (in_array('good-music',$catSlugs)){
$post_cat = 'good-music';
} else {
$post_cat = 'not-good-music';
}
get_template_part( 'template-parts/post/content', $post_cat );
?>
<?php
endwhile; // End of the loop.
?>
It is important that this code only appear where there is a query to loop against.
Specifically, the file single.php in your theme should be the default file for displaying a single post, regardless of category. When you navigate to the url of a single post, this layout should be triggered.
As part of that triggering, a wordpress query of just that post is returned to be looped through.
Then, the code from while ( have_posts() ) : the_post(); until endwhile; will run one time, because there is a single post to be processed.
If there were more than one post, such as on a category page or on your default post listing page, then the code inside of that while loop would run as many times as there are posts in the query for that layout.
If you were to place the code in the header, it won't work because the header is prepared independently of the loop that runs on this page.
You could run a custom WP_query() in the header, but that is rarely a good way to handle site content.
In this situation it would not be appropriate, because you are customizing content of existing posts, and only differentiating based upon category.
So, just use the standard layouts files with custom layout parts.
I stripped out the divs in the loop below, because you may or may not be using bootstrap.
After this code is placed on your page, you would create files called content-good-music.php and content-not-good-music.php in YOUR_THEME_DIR/template-parts/post/ directory. The key is that you would add whatever your category slug is to the end of your
These files will contain the unique markup for these kinds of posts. You can also use a similar logic in your post listing loop to give the listed posts for each category their own unique php files.
Here's some get_template_part() documentation.
https://developer.wordpress.org/reference/functions/get_template_part/