Hook added to the_content seems to be called multiple times

Question

I have the following code running in a plugin:

 add_filter('the_content','thousand_pay');

//Callback function
function thousand_pay($content)
{
    echo $content;

    if( !in_category( 'Stories') )

    {
        return;
    }
    ?>
<hr></hr>
[Some HTML]
<?php

    return
}

For some reason, on individual posts' pages the HTML gets printed multiple times:

Can anyone think of why this would be? I read here that I might have to add to the conditional to check is_singular() and is_main_query(), so it would look like if(!in_category('Stories') || !is_singular() || !is_main_query(), but that just seems to stop the HTML getting printed at all on a post page. Any ideas?

Answer 1

It is normal for content to be accessed multiple times. For example SEO plugins need to do this to access it and generate meta data from.

Also it is a filter hook. Filters should never echo anything to the page, they are meant to modify passed value and return it.

If you do want to do something at that point, but only within the loop then in_the_loop() is condition you need.

Answer 2

I was having the same issue. My the_content filter was being called multiple times and this was slowing down page load as my the_content filter was calling an external API. So in my case, the API was being queried multiple times for the same data.

I tried using in_the_loop(), is_singular() and is_main_query() but sometimes, depending on the theme, those failed to limit calls to my filter to one time.

So I added a constant to my filter and that seems to have fixed the issue.

Here's an example of how to limit your calls to the the_content filter to one time:

add_filter( 'the_content', 'se225721_the_content' );

function se225721_the_content( $content ) {

    if ( ! in_the_loop() ) {
        return $content;
    }

    if ( ! is_singular() ) {
        return $content;
    }

    if ( ! is_main_query() ) {
        return $content;
    }

    $content = ucwords( $content );

    remove_filter( 'the_content', 'se225721_the_content' );

    return $content;
}

Hope that helps!

Eric

Answer 3

I have found another way to achieve this by using the did_action() function and a custom action hook.

Here is the solution:

$custom_hook = 'my_plugin_prefix_a_custom_action_hook';
function my_plugin_prefi_my_filter_callback($content){
  if(did_action($custom_hook) == 0){
    do_action($custom_hook);
    //your filter action code goes here: modification of $content
  }
  return $content;
}

function my_plugin_prefix_custom_action_hook_callback(){
  //do nothing
}
add_action($custom_hook, 'my_plugin_prefix_custom_action_hook_callback');

At first the run count of action hook $custom_hook will be 0 and do_action($custom_hook); statement will make the run count of $custom_hook to 1 and this will prevent subsequent execution of the body of the if statement.