ACF PRO taxonomy term field in WordPress submenu - wordpress

Question

I have a question that I can't seem to find the right approach to.
I'm currently developing a WordPress site whereby a custom submenu is required. In said submenu, a list of category terms is displayed (incidentally, a list of years – 2003-2017). For each of these years, I have created an image field using the brilliant Advanced Custom Fields PRO plugin. The idea is that an image can be uploaded for a year in the “Edit Category” page. So far, so good. This image would then be shown in the submenu alongside the year, and here's where I am stumped.
What I am having trouble with is figuring out how I am going to check for that field in the submenu and fetch it.
I'll include the code for the custom nav walker below. Any help would be greatly appreciated!
class Nav_Header_Walker extends Walker_Nav_Menu {
public function display_element( $element, &$children_elements, $max_depth, $depth, $args, &$output ) {
if ( ! $element ) {
return;
}
$id_field = $this->db_fields['id'];
$id = $element->$id_field;
// Display this element.
$this->has_children = ! empty( $children_elements[ $id ] );
if ( isset( $args[0] ) && is_array( $args[0] ) ) {
$args[0]['has_children'] = $this->has_children; // Backwards compatibility.
}
$cb_args = array_merge( array( &$output, $element, $depth ), $args );
call_user_func_array( array( $this, 'start_el' ), $cb_args );
// Descend only when the depth is right and there are children for this element.
if ( ( 0 === $max_depth || $max_depth > $depth + 1 ) && isset( $children_elements[ $id ] ) ) {
foreach ( $children_elements[ $id ] as $child ) {
if ( ! isset( $newlevel ) ) {
$newlevel = true;
// Start the child delimiter.
$cb_args = array_merge( array( &$output, $depth ), $args );
/** Additional check for custom addition of id to sub-level */
if ( $element->post_name = 'Megatron' ) {
$cb_args['sub_menu_id'] = 'megatron';
}
/** End custom check */
call_user_func_array( array( $this, 'start_lvl' ), $cb_args );
}
$this->display_element( $child, $children_elements, $max_depth, $depth + 1, $args, $output );
}
unset( $children_elements[ $id ] );
}
if ( isset( $newlevel ) && $newlevel ) {
// End the child delimiter.
$cb_args = array_merge( array( &$output, $depth ), $args );
call_user_func_array( array( $this, 'end_lvl' ), $cb_args );
}
// End this element.
$cb_args = array_merge( array( &$output, $element, $depth ), $args );
call_user_func_array( array( $this, 'end_el' ), $cb_args );
}
public function start_lvl( &$output, $depth = 0, $args = array(), $sub_menu_div = null ) {
$indent = str_repeat( "\t", $depth );
if ( $sub_menu_div ) {
$output .= "\n$indent<div id=\"$sub_menu_div\"><ul class=\"sub-menu\">\n";
} else {
$output .= "\n$indent<ul class=\"sub-menu\">\n";
}
}
function end_lvl( &$output, $depth = 0, $args = array() ) {
$indent = str_repeat( "\t", $depth );
$output .= "$indent</ul></div>\n";
}
}

Answer 1

In case anybody ever comes across this rather niche issue in the future, I figured out what I approach I needed.
Adding the following block of code to the end of what I included in my original question did the trick.
Pay close attention to how I retrieve the ACF image field (standard way to get a taxonomy field, if you're not familiar with it), using $item->object and $item->object_id.
It’s then just a case of altering the output to include the background image for each menu item, using the conditional to check whether said item is a category link and is the correct depth (i.e. if it is a submenu item). If it isn't both of those, it doesn't bother with the background image.
function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ) {
if ( in_array( 'menu-item-object-category', $item->classes ) && $depth > 0 ) {
// Get the ACF PRO image field (I have replaced my field with 'field_name', change this to your field)
$thumb = get_field( 'field_name', $item->object . '_' . $item->object_id );
$before = '<li class="' . implode( ' ', $item->classes ) . '">';
$after = '</li>';
// Attributes
$attributes = ! empty( $item->attr_title ) ? ' title="' . esc_attr( $item->attr_title ) .'"' : '';
$attributes .= ! empty( $item->target ) ? ' target="' . esc_attr( $item->target ) .'"' : '';
$attributes .= ! empty( $item->xfn ) ? ' rel="' . esc_attr( $item->xfn ) .'"' : '';
$attributes .= ! empty( $item->url ) ? ' href="' . esc_attr( $item->url ) .'"' : '';
$attributes .= ' style="background-image: url(' . $thumb['url'] . ')"';
$item_output = sprintf( '%1$s<a%2$s>%3$s%4$s%5$s</a>%6$s',
$before,
$attributes,
$args->link_before,
apply_filters( 'the_title', $item->title, $item->ID ),
$args->link_after,
$after
);
$output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );
} else {
$before = '<li class="' . implode( ' ', $item->classes ) . '">';
// link attributes
$attributes = ! empty( $item->attr_title ) ? ' title="' . esc_attr( $item->attr_title ) .'"' : '';
$attributes .= ! empty( $item->target ) ? ' target="' . esc_attr( $item->target ) .'"' : '';
$attributes .= ! empty( $item->xfn ) ? ' rel="' . esc_attr( $item->xfn ) .'"' : '';
$attributes .= ! empty( $item->url ) ? ' href="' . esc_attr( $item->url ) .'"' : '';
$item_output = sprintf( '%1$s<a%2$s>%3$s%4$s%5$s</a>%6$s',
$before,
$attributes,
$args->link_before,
apply_filters( 'the_title', $item->title, $item->ID ),
$args->link_after,
$args->after
);
$output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );
}
}
function end_el( &$output, $item, $depth = 0, $args = array() ) {
$output .= "</li>\n";
}