Prevent multiple add_to_head() calls

Question

In function display_field(), if a fieldtype needs to use ee()->cp->add_to_head('/path/to/foo.css') and ee()->cp->add_to_foot('/path/to/bar.js'), how can I get it to do so only once, even when the Publish page may have multiple instances of that field?

Answer 1

Use the session cache:

if (ee()->session->cache(__CLASS__, __FUNCTION__) === FALSE)
{
  ee()->cp->add_to_head('/path/to/foo.css');

  ee()->session->set_cache(__CLASS__, __FUNCTION__, TRUE);
}

Your code will only run once per page load.