Gravity Forms - Checkbox Dynamic Population

functions.php

// When true, the form will be saved to DB after dynamic population
define('EO_SAVE_FORM_ON_PRE_RENDER', true);

// Adds a filter to form id 7. Replace 26 with your actual form id
add_filter('gform_pre_render_7', 'eo_populate_checkbox');
add_filter('gform_admin_pre_render_7', 'eo_populate_checkbox');

function eo_populate_checkbox($form) {

    if (EO_SAVE_FORM_ON_PRE_RENDER)
      $the_form = RGFormsModel::get_form_meta($form['id']);
    else
      $the_form = &$form;

    // Creating choices
    $choices = array(
      array('text' => 'Choice 1', 'value' => 'choice1'),
      array('text' => 'Choice 2', 'value' => 'choice2'),
      array('text' => 'Choice 3', 'value' => 'choice3'),
    );

    $inputs = array(
      array('label' => 'Choice 1', 'id' => '2.1'), // replace 2 in 2.1 with your field id
      array('label' => 'Choice 2', 'id' => '2.2'), // replace 2 in 2.2 with your field id
      array('label' => 'Choice 3', 'id' => '2.3'), // replace 2 in 2.3 with your field id
    );

    // Adding items to field id 2. Replace 2 with your actual field id.
    // You can get the field id by looking at the input name in the markup.
    foreach ($the_form['fields'] as &$field) {
        // replace 2 with your checkbox field id
        if ($field['id'] == 2) {
            $field['choices'] = $choices;
            $field['inputs'] = $inputs;
        }
    }

    // Save form to database, if constant is set to true
    if (EO_SAVE_FORM_ON_PRE_RENDER)
      RGFormsModel::update_form_meta($form['id'], $the_form);

  return $the_form;
}