I'd like to change the form that opens when adding an Activity to a Case (depending on activity type). Specifically, I'd like to add a field. I tried finding the fields I want to change in sites/all/modules/civicrm/CRM/Case/Form/Activity.php but couldn't find them. It seems like the buildQuickForm() function is only creating some of the visible fields but not all. I also thought about writing an extension based on the hook_civicrm_buildForm function. I want to start checking if $formName == 'CRM_Case_Form_Activity' but after that I don't really know where to start. Can anyone give me a hint?

Edit: I found an extension changing the same location looking like this (How can I set "Assigned To" for an Activity to default to the logged-in user name?):

function myextension_civicrm_buildForm($formName, &$form) {
  if ($formName == 'CRM_Activity_Form_Activity' && $form->getAction() == CRM_Core_Action::ADD) {
    $form->setDefaults(array('assignee_contact_id' => $form->_currentUserId));

Is there anything like $form->addField or something?

  • Did you look at custom fields? (Admin - Customize - Custom Fields) You can create them for activities for either all types or just some types.
    – Demerit
    Oct 20, 2020 at 11:22
  • I tried that now, but the field doesn't appear. I think this is because the activity where I want to add a field is not a normal activity but a "create email" activity
    – emma
    Oct 20, 2020 at 11:46
  • Ok yes emails are a bit different.
    – Demerit
    Oct 20, 2020 at 11:48

1 Answer 1


you need to create an extension and use the buildForm hook.

More information on creating an extension can be found here: https://docs.civicrm.org/dev/en/latest/extensions/

More information on the buildForm hook: https://docs.civicrm.org/dev/en/latest/hooks/hook_civicrm_buildForm/ This contains an example of adding a field.

Another example of adding a field with the buildForm hook:

if ($studyNumber) {
  $form->addElement('text', 'study_number', "Study Number", ['readonly' => 'readonly']);
  $form->setDefaults(['study_number' => $studyNumber]);
  CRM_Core_Region::instance('page-body')->add(['template' => 'CRM/Nihrbackbone/nbr_study_number.tpl',]);

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