ACF Importing Children XML Into Custom Fields

example.xml

<page>
	<post>
		<Panel>
			<Name>Gemma</Name>
			<PanelImage>
				http://unsplash.it/400/500
			</PanelImage>
			<ID>1</ID>
		</Panel>
		<Panel>
			<Name>Walle</Name>
			<PanelImage>
				http://unsplash.it/400/500
			</PanelImage>
			<ID>1</ID>
		</Panel>
	</post>
	<post>
		<Panel>
			<Name>Finnick</Name>
			<PanelImage>
				http://unsplash.it/400/500
			</PanelImage>
			<ID>2</ID>
		</Panel>
		<Panel>
			<Name>Emily</Name>
			<PanelImage>
				http://unsplash.it/400/500
			</PanelImage>
			<ID>2</ID>
		</Panel>
	</post>
</page>

functions.php

<?php

  add_action('pmxi_update_post_meta', 'update_panels', 10, 3);

  function update_panels($pid, $m_key, $m_value) {
      if ( $m_key == 'import_unprocessed') {

          $arr = preg_split('/\n|\r\n?/', $m_value);
          update_post_meta($pid, 'test', count($arr));
          for ($i = 0; $i < (count($arr) - 1); $i++) {
            $col = explode(',', $arr[$i]);
            update_post_meta($pid, 'name_'.$i, $col[0]);
            update_post_meta($pid, 'image_'.$i, $col[1]);
          }
      }
  }

  // Alternative Example For Flexible Content
  add_action('pmxi_update_post_meta', 'update_panels', 10, 3);
    function update_panels($pid, $m_key, $m_value) {
        $updatable_actions = [];

        if ( $m_key == 'import_panels') {
            $panelarr = [];

            $arr = explode('***LINE***', $m_value);

            update_post_meta($pid, 'test', count($arr));

            for ($i = 0; $i < (count($arr) - 1); $i++) {
              $col = explode('***,***', $arr[$i]);
              $panelarr[] = 'field_btm_panel';

              array_push($updatable_actions, [ 'key' => 'field_btm_content_layout_'.$i.'_field_btm_panel_image', 'value' => $col[0] ]);
              array_push($updatable_actions, [ 'key' => '_field_btm_content_layout_'.$i.'_field_btm_panel_image', 'value' => 'field_btm_panel_image' ]);

              array_push($updatable_actions, [ 'key' => 'field_btm_content_layout_'.$i.'_field_btm_panel_content', 'value' => $col[1] ]);
              array_push($updatable_actions, [ 'key' => '_field_btm_content_layout_'.$i.'_field_btm_panel_content', 'value' => 'field_btm_panel_content' ]);
            }

            array_push($updatable_actions, [ 'key' => 'field_btm_content_layout', 'value' => serialize($panelarr) ]);
            array_push($updatable_actions, [ 'key' => '_field_btm_content_layout', 'value' => 'field_btm_content_layout' ]);

        }

        foreach ($updatable_actions as $action) {
          update_post_meta($pid, $action['key'], $action['value']);
        }
    }

wp_all_import_field.md

Add the following to a custom field that you use just for importing. You can call it whatever you like. Then, once the import is complete, you can hook into the pmxi_update_post_meta action - and process the imports as you like.

It is a bit reminiscent of what you would do in hackerrank.

[FOREACH({Panel})]
{Name},{PanelImage}
[ENDFOREACH]

[FOREACH({Panel})]
{Name}***,***{PanelImage}***LINE***
[ENDFOREACH]