Symfony2: How to validate an input field is not-blank, only when checkbox is true?

Question

Within Symfony2 how to validate an inputfield is not-blank, only when the value of a checkbox is 1 (True) - otherwise blank is allowed?

To be more precise, I have a

Answer 1

could you do something like this ?

/**
 * @Assert\True()
 */
public function customValidate()
{
    return (!$this->checkboxField) or (strlen($this->inputField) > 0);
}