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I'm using the Advanced Custom Fields plugin to create a metabox with a list of all posts of specific post type, for the user to be able to select related posts for a page. You can see a simple documentation of this functionality here: http://www.advancedcustomfields.com/docs/field-types/post-object/

It's supposed to return a post object. However, I noticed when I try to query it to get any data (title, content, thumbnail etc.) nothing happens. I'm using a foreach loop like in the example (for multiple post chosen) and it returns the following error:

Warning: Invalid argument supplied for foreach()

I thought maybe the option didn't return any post objects, so I've done a var_dump expecting it to spit out null, but instead it showed bool(false).

Now, I'm not a PHP expert by any means, so I'm not sure what that bool(false) means exactly and why would it be what the function returns.

Does anyone have any idea what could be causing the problem? I should add that I get the same result with a very similar function of ACF described here: http://www.advancedcustomfields.com/docs/field-types/repeater/

Thanks in advance!

EDIT: Added code that I'm using:

<div class="insights-features group">

    <?php $featured_articles = get_field('featured_articles'); ?>

    <?php foreach ($featured_articles as $post_object): ?>
        <?php $category = get_the_category($post_object->ID); ?>
        <div class="col2">
            <a href="<?php echo get_permalink($post_object->ID); ?>">
                <?php echo get_the_post_thumbnail($post_object->ID, array(320,302)); ?>
                <p class="descr"><?php echo get_the_title($post_object->ID) ?> by <?php echo get_the_author($post_object->ID) ?> <span>Read In <?php echo $category[0]->cat_name; ?></span></p>
    <?php endforeach; ?>    

</div><!-- /insights-features -->

<div class="main col4 group">

    <?php if ( have_posts() ) while ( have_posts() ) : the_post(); ?>

        <div class="post group">
            <div class="post-head">
                <h5 class="category"><?php the_category(', '); ?></h5>
                <h2><a href="<?php the_permalink(); ?>"><?php the_title();?></a></h2>
                <p class="meta"><span class="location">Shanghai</span> <span class="date"><?php the_time('m.d.y, h:iA'); ?></span> by <?php the_author_link(); ?></p>
            </div><!-- /post-head -->
            <?php the_excerpt();?>
        </div><!-- /post -->

    <?php endwhile; ?>

</div><!-- /main -->

This is a snippet from the index.php template – it's supposed to display 3 posts chosen via ACF in insights-features section and then a normal archive loop for the normal flow of posts. As you can tell, I'm using ACF fields outside of the loop.

Also worth mentioning: the custom fields are on a page that is setup to display blog posts in WordPress' settings. Hope that clears things out.

EDIT: Figured it out.

It seems like this didn't work because the page where the custom fields were set up was used as "Posts Page" in WordPress (using index.php file). I copied the code from index.php and created a new page template, set up the page to use this template and removed its selection from "Posts Page" in Reading settings. This seems to have done the trick.

Not sure why it was causing a conflict but it does seem reasonable that it did...

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Are you using the_field/get_field inside or outside The Loop? - please add a summary of your code to the question –  brasofilo Apr 26 '12 at 12:15
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2 Answers

Did you purchase and activate the repeater field portion of the plugin? That's the only portion that would return an array to use foreach with outside The Loop (that I'm aware of). Either way, the code calling the ACF fields needs to live inside The Loop as @brasofilo said if you're wanting two different chunks like this, you'll find it easier with two loops (with two different queries) on the page, the first to call the 3 posts for the first section, the second to call the normal loop.

If you're stumped, I would start by adding a print_r($featured_articles); after you set that variable on the second line. That will let you know if there's anything in there, and if it's an array that you can actually use foreach with.

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The Post Object and Relationships modules of ACF also return arrays when there are multiple posts selected: "The API will return either a single post object or an array of post objects. This example shows use of multiple post objects" – I will definitely try making a loops to use the ACF code there. –  Justine Apr 26 '12 at 18:41
I think I figured it out, see latest edit. –  Justine Apr 26 '12 at 18:57
That would make sense, since the posts page isn't designed to output any content of its own. Glad you got it working again! –  SickHippie Apr 26 '12 at 20:34
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The problem was (you have solved, I see) that get_field with no second param is designed to get the meta values from the current post.

On the contrary, you called get_field in the index.php, outside and before the loop, so there is no current post, and for this reason get_field return false: function doesn't know in which page search for the required field.

Once you removed the "Posts Page" option now the page use its own page template and in this way get_field can recognize the id of the current page and correctly return the value.

Another solution was, if you wanted leave code in index.php, and leave the "Posts Page" option, get the id of the page setted as "Posts Page" and use this id with get_field to retrieve the featured articles, something like this:

  $homepageid = get_option('page_for_posts') ? : false;
  $featured_articles = $homepageid ? get_field('featured_articles', $homepageid) : '';
  if ( ! empty($featured_articles) ) {

    echo '<div class="insights-features group">';

    foreach ( (array)$featured_articles as $post_object) :
        $category = get_the_category($post_object->ID);

        <div class="col2">

     <?php endforeach; ?>

    echo '</div>';

Note that this code can work not only in index.php, but in every template file: page, single, taxonomy archive, and so on... even in the header.php or footer.php, the only condition to work is that a page is selected in "Posts Page" in Reading settings and the featured articles are selected using ACF in this page.

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