Example of using the gform_pre_render filter hook to perform calculations, returning results in dynamically populated fields. See documentation links for more info. http://www.gravityhelp.com/documentation/page/Gform_pre_render http://www.gravityhelp.com/documentation/page/Using_Dynamic_Population

gistfile1.php

<?php

/**
* excerpt from compound classroom field, for example purposes only
* the real class is over 700 lines
*/
class OlpcGfClassroomField {

    /**
    * hook into Gravity Forms
    */
    public function __construct() {
        add_filter('gform_pre_render', array($this, 'gformPreRender'));
    }

    /**
    * count the students and training participants in the classroom fields
    * @param array $form
    * @return array
    */
    public function gformPreRender($form) {
        $students = 0;
        $participants = 0;
        $studentsField = false;
        $participantsField = false;

        // search fields to find classroom fields, and our dynamically populated fields
        foreach ($form['fields'] as $field) {
            // check for our custom field type
            if ($field['type'] == OLPCGF_FIELD_CLASSROOM) {
                $values = $this->getPost($field['id']);

                if (is_numeric($values['students']) && $values['students'] > 0) {
                    $students += $values['students'];
                }

                if ($values['trainingparticipant']) {
                    $participants++;
                }
            }

            // check for dynamically populated fields with our special keys
            elseif ($field['inputName'] == 'olpcgf_total_class_students') {
                $studentsField = $field;
            }
            elseif ($field['inputName'] == 'olpcgf_total_class_training') {
                $participantsField = $field;
            }
        }

        // set total students field
        if ($studentsField) {
            $_POST['input_' . $studentsField['id']] = $students;
        }

        // set total participant laptops field
        if ($participantsField) {
            $_POST['input_' . $participantsField['id']] = $participants;
        }

        return $form;
    }

    /**
    * get input values for compound field
    * @param integer $field_id
    * @return array
    */
    protected static function getPost($field_id) {
        $values = rgpost('olpcgf_' . $field_id);

        if (is_array($values)) {
            $values = array (
                'fname' => $values[1],
                'lname' => $values[2],
                'email' => $values[3],
                'mobile' => $values[4],
                'role' => isset($values[5]) ? $values[5] : array(),
                'level' => isset($values[6]) ? $values[6] : array(),
                'students' => GFCommon::to_number($values[7]),
                // checkbox, may not be present:
                'trainingparticipant' => isset($values[8]) ? $values[8] : '',
            );
        }
        else {
            $values = false;
        }

        return $values;
    }

}

// create an instance of the class, which hooks into Gravity Forms
// (references to the class keep it alive, no need to store in a variable)
new OlpcGfClassroomField();