use Symfony\Component\Form\Extension\Core\Type\TextType; use Symfony\Component\Form\FormBuilderInterface; use Symfony\Component\Form\DataTransformerInterface; use Symfony\Component\Form\Extension\Core\DataTransformer\CallbackTransformer; class CreditCardFormType extends AbstractType { public function buildForm(FormBuilderInterface $builder, array $options) { // Add a text field for the credit card number $builder->add('creditCardNumber', TextType::class); // Add a view transformer to the creditCardNumber field $builder->get('creditCardNumber')->addViewTransformer(new CallbackTransformer( // Transform data displayed in form field function ($originalCreditCardNumber) { // Transform credit card number into visually appealing format $formattedCreditCardNumber = // Code to format credit card number return $formattedCreditCardNumber; }, // Transform data submitted by user function ($submittedCreditCardNumber) { // Convert visually formatted credit card number back to original format $originalCreditCardNumber = // Code to convert number back return $originalCreditCardNumber; } )); } }In this example, the `creditCardNumber` field is transformed using a `CallbackTransformer`, which allows for simultaneous transformation of displayed data and user-submitted data. The first anonymous function is used to format the credit card number for display in the form field, while the second function is used to convert the formatted number back to its original format when submitted by the user. Overall, the `addViewTransformer()` method is a powerful tool for customizing form behavior in Symfony applications. Its flexibility and ease of use make it a popular choice among developers working with Symfony's form builder.