silverstripe-userforms/code/model/editableformfields/EditableCheckbox.php

<?php
/**
 * EditableCheckbox
 *
 * A user modifiable checkbox on a UserDefinedForm
 *
 * @package userforms
 */

class EditableCheckbox extends EditableFormField {

	private static $singular_name = 'Checkbox Field';

	private static $plural_name = 'Checkboxes';

	private static $db = array(
		'CheckedDefault' => 'Boolean' // from CustomSettings
	);

	/**
	 * @return FieldList
	 */
	public function getCMSFields() {
		$fields = parent::getCMSFields();

		$fields->replaceField('Default', CheckboxField::create(
			"CheckedDefault",
			_t('EditableFormField.CHECKEDBYDEFAULT', 'Checked by Default?')
		));

		return $fields;
	}

	public function getFormField() {
		$field = CheckboxField::create($this->Name, $this->EscapedTitle, $this->CheckedDefault)
			->setFieldHolderTemplate('UserFormsCheckboxField_holder')
			->setTemplate('UserFormsCheckboxField');

		$this->doUpdateFormField($field);

		return $field;
	}

	public function getValueFromData($data) {
		$value = (isset($data[$this->Name])) ? $data[$this->Name] : false;

		return ($value) ? _t('EditableFormField.YES', 'Yes') : _t('EditableFormField.NO', 'No');
	}

	public function migrateSettings($data) {
		// Migrate 'Default' setting to 'CheckedDefault'
		if(isset($data['Default'])) {
			$this->CheckedDefault = (bool)$data['Default'];
			unset($data['Default']);
		}

		parent::migrateSettings($data);
	}
}