Time for Action – Implement a Digg link

Let's create a function to display a Digg submit link using information from the post.

Then we will implement this function into our theme, to show the link just after the post content.

Well done! You have created your first working WordPress plugin!

What just happened?

When WordPress loads a post, the single.php template file from the currently active WordPress theme is ran. We added a line to this file that calls our plugin function WPDiggThis_Link() just after the content of the post is displayed:

<?php the_content('<p class="serif">Read the rest of this entry &raquo;</p>'); ?>

<?php if (function_exists(WPDiggThis_Link)) echo WPDiggThis_Link(); ?>

We use function_exists()to check our function because it exists only if our plugin is installed and activated. PHP will generate an error if we try to run a nonexistent function. But if we deactivate the plugin later, we don't want to cause errors with our theme. So, we make sure that the function exists before we attempt to run it.

Assuming that the plugin is present and activated, the WPDiggThis_Link() function from our plugin is ran. The first part of the following function gets information about our post and assigns it to variables:

/* Show a Digg This link */
function WPDiggThis_Link()
{
    global $post;
    
    // get the URL to the post
    $link=urlencode(get_permalink($post->ID));
    
    // get the post title
    $title=urlencode($post->post_title);
    
    // get first 350 characters of post and strip it off HTML tags
    $text=urlencode(substr(strip_tags($post->post_content), 0, 350));

We use the urlencode() PHP function for all the parameters that we will pass to the final link. This will ensure that all the values are formatted properly.

The second part uses this information to construct a Digg submit link:

    // create a Digg link and return it    
    return '<a >Digg This</a>';

}

It returns this HTML text so that it gets added to the WordPress output at the point where the function is called – just after the post is displayed. Therefore, the link appears right after each post—which is convenient for the user who has just finished reading the post.

Using the Digg API

Usually, when using the functionalities of third-party sites, as we are doing in our example with Digg, we would search for the API documentation first. Almost all the major sites have extensive documentation available to help developers use their services in an effective way.

Digg is no exception, and if you search the Internet for the digg button api you will find a page at http://digg.com/tools/integrate that will have all the details we need in order to implement our Digg functionality.

Digg allows us to use several different ways of using their service.

For the start, we will display just a Digg link. Later, we will expand it and also display a normal button.

Here is what the Digg documentation says about formatting a submit link.

Acquiring post information

WordPress provides a number of ways to get information about the current post.

One of them involves using the global variable $post, which stores all the relevant information for the current post. We have used it in our example to extract the post title and content, but it can also be used to get other information such as post category, status and so on.

WordPress also offers an array of functions we could have used to access post information such as get_the_title() and get_the_content().

The main difference between using these functions and accessing post data directly using $post variable is in the end information we get. The $post variable contains raw information about the post, just as the user wrote it. The functions mentioned above take the same raw information as a starting point, but could have the final output modified by external factors such as other active plugins.

Editing the theme files

In our example, we had to edit our theme in order to place the Digg link under the post content. WordPress allows for easy theme editing through the built-in Theme Editor panel.

After selecting the theme you want to edit, you will be presented with a number of options. Every theme consists of various PHP template files, each covering different blog functionalities.

Here is a reference table detailing the most commonly used template files.

Always be careful when editing the theme files as any kind of mistake in your syntax can cause an error in displaying the page. It is therefore good practice to first backup theme files, so you can safely revert to them afterwards.

Have a go Hero

Our plugin already has useful functionality. Try to customize it by: