In this series, I introduce:

• Assign categories and taxonomies to attachments,
• Query media files by category so you can output them in a custom loop,
• Use the image classification query to display it on the archive page,
• Add an image to a category or taxonomy term as a "featured image" for the category or term

In Part 1, I demonstrated how to create a new taxonomy for attachments. In Part 2 I showed you how to create a custom template file for your documents and add a loop to display links to media files for each document, and in Part 3 I showed you how to create a custom template file for your documents and in Part 3 I showed you how to create a custom template file for your documents. # Created a custom template file taxonomy that displays all images with a given term as a gallery style archive page. In this final part, I'll demonstrate something slightly different: how to assign a category to an image, and then edit the category's archive template to display that image as a "Featured Image" for that category. You can also do this with tags or taxonomy terms using a very similar technique.

In this tutorial, I will create a theme that will be a child theme of Twenty Four. The theme will include a function file and a custom template file for the category archive. You can download the theme in a code package.

What do you need

To follow this tutorial, you need the following:

Development Installation of WordPress

• FTP access (or MAMP or similar if you're working locally)
• Code Editor

1.

Apply categories to attachments By default, WordPress does not allow you to assign categories and tags to attachments, which you will need to be able to do for this tutorial. Fortunately, this problem is easy to fix, as I demonstrated in my previous tutorial on assigning categories and tags to attachments.

Note: This technique works with tags and categories, if you do this with your own taxonomy you will need to specify the attachment as the post type to which your taxonomy applies when registering. You can do this by following part one of this series.

In your theme, create a file called

functions.php

and add the following code to it: <pre class='brush:php;toolbar:false;'>&lt;?php // add categories to attachments function wptp_add_categories_to_attachments() { register_taxonomy_for_object_type( 'category', 'attachment' ); } add_action( 'init' , 'wptp_add_categories_to_attachments' ); ?&gt; </pre> This uses the

register_taxonomy_for_object_type()

function to add a category to the attachment. Now, when you view the Media Library screen, you will see that categories are enabled. The next step is to add some images - just one image per category. You'll also want to add another category called "Featured" and make sure every image you want to use in this way falls into that category as well.

Below you can see a sample media editing screen showing the categories:

You can also view all images that I assigned the correct category:

Finally, I'm going to add some dummy posts to my site and put them into relevant categories to have some content to show up in my archive pages:

2.創(chuàng)建類別模板

下一步是創(chuàng)建自定義類別模板。由于我的主題是二十四的子主題，我將復(fù)制該主題的 category.php 文件并將其復(fù)制到我的子主題，并對開頭注釋進行一些更改：

<?php  
/**   
 * The template for displaying Category pages   
 * Custom template which displays a featured image first.   
 * Supports Part 4 of tutorial series on Advanced Use of Images in WordPress for WPTutsplus   
 */ get_header();  ?>
<section class="content-area" id="primary">
  <div class="site-content" id="content" role="main"><?php if ( have_posts() ) : ?>
    <header class="archive-header">
      <h1 class="archive-title"></h1>
        <?php 
          // Show an optional term description.
          $term_description = term_description();
          if ( ! empty( $term_description ) ) :
            printf( '<div class="taxonomy-description">%s</div>', $term_description );
          endif;
        ?>
    </header><!-- .archive-header -->

<?php   
// Start the Loop. 					   
while ( have_posts() ) : the_post(); 					     
      /* 					       
       * Include the post format-specific template for the content. If you want to 					            
       * use this in a child theme, then include a file called called content-___.php 					            
       * (where ___ is the post format) and that will be used instead. 					       
       */ 					     
      get_template_part( 'content', get_post_format() ); 					   
    endwhile; 			
		   
    // Previous/next page navigation. 					   
    twentyfourteen_paging_nav();			   
  else : 					     
    // If no content, include the "No posts found" template. 					              
    get_template_part( 'content', 'none' ); 				   
  endif;    
  ?></div><!-- #content -->
</section><!-- #primary -->

<?php  get_sidebar( 'content' ); get_sidebar(); get_footer(); ?>

3.向類別模板添加自定義查詢

在主循環(huán)上方，使用 WP_Query 添加自定義循環(huán)。在結(jié)束 </h1> 標(biāo)記后插入以下內(nèi)容：

<?php  
// display a featured image for the category  
// identify the current category  
$currentcat = get_queried_object(); 
$currentcatname = $currentcat->slug;
?>

使用 get_queried_object() 標(biāo)識當(dāng)前顯示的類別。

下面，使用 WP_Query 定義自定義查詢的參數(shù)：

<?php    
// define query arguments for the featured image    
$args = array( 	     
    'post_type' => 'attachment',
    'post_status' => 'inherit',
    'category_name' => $currentcatname,
  );
  $query = new WP_Query( $args );
?>

這標(biāo)識當(dāng)前類別以及“特色”類別中的所有附件。請注意，由于 WordPress 設(shè)置附件帖子狀態(tài)的方式，您需要包含 'post_status' => 'inherit' 作為參數(shù)。

現(xiàn)在在此下方添加循環(huán)：

<?php  
  // The Loop  while ( $query->have_posts() ) : $query->the_post();
  // define attributes for image display
  $imgattr = array(
		'alt'   => trim( strip_tags( get_post_meta( $attachment_id, '_wp_attachment_image_alt', true ) ) ),
	);

  // output the image ?>
  <div class="category-image"></div>
<?php 
endwhile;  
// reset the query so the default query can be run  
wp_reset_postdata(); ?>

確保您不要錯過最后的 wp_reset_postdata() ，否則類別存檔的主查詢將無法工作。

添加完所有這些后，保存您的類別模板并查看您的類別存檔頁面之一。它應(yīng)該類似于本教程開頭的屏幕截圖。

摘要

在這個由四個教程組成的系列中，我演示了一些在 WordPress 中處理圖像的高級技術(shù)。其中包括：

• 注冊專門用于附件的分類
• 使用自定義模板創(chuàng)建 dosucmtn 列表頁面
• 再次使用自定義模板創(chuàng)建圖庫頁面以顯示給定類別中的圖像
• 為每個類別創(chuàng)建“特色圖片”并將其顯示在類別存檔頁面上。

正如您所見，您可以在 WordPress 中對圖像和媒體執(zhí)行更多操作，而不僅僅是將它們附加到帖子或?qū)⑺鼈冇米魈厣珗D像。只要發(fā)揮一點想象力，您就可以像任何其他帖子類型一樣查詢它們，并輸出文檔或顯示圖像的鏈接。

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