Module Development

Validate a Form via the Form Controller for Drupal 8, 9, and 10

When your module defines the form and the form controller, you can add your validation logic as part of the form controller. This is done via the implementation of a validateForm() method. The FormBuilder service will automatically invoke this method at the appropriate time during the process of submitting a form. While the validateForm() method is required by \Drupal\Core\Form\FormInterface, an empty method will fulfill that requirement. It's up to you to provide appropriate validation code inside the method.

In this tutorial we'll:

  • Use the validateForm() method of a form controller to verify user input
  • Demonstrate how to raise errors on a form element when it doesn't pass validation

By the end of this tutorial you should know how to validate your custom forms.