Module Development

Overview: Drupal's Form API for Drupal 8, 9, and 10

Drupal's Form API (FAPI) is a comprehensive framework for managing forms within Drupal. The Form API extends the Render API, providing a structured approach to form creation, validation, and submission. It offers an abstraction layer over HTML forms and HTTP form handling, simplifying the process of capturing and processing user input securely and efficiently. Forms are integral to content management systems like Drupal, enabling user interactions ranging from content creation to configuration settings. For module developers, using the Form API is essential for building interactive and dynamic websites.

In this tutorial, we'll:

  • Discuss the relationship between the Form API and the Render API.
  • Highlight the significance of forms in Drupal and the role of the Form API in managing them.
  • Outline the life cycle of a Drupal form, from definition to processing, including the role of form controllers.

By the end of this tutorial, you should grasp the fundamentals of the Form API and be prepared to construct and manage forms in Drupal modules.

Goal

Understand the role of Drupal's Form API in creating, validating, and processing forms.

Prerequisites

The importance of forms in Drupal

Forms are prevalent in Drupal, enabling users to create content, configure module settings, and more. The Form API facilitates these interactions through secure standardized methods for form management.

Form API: render arrays for forms

The Form API extends the Render API, providing form-related render elements (#type) to handle all kinds of user input in a consistent manner. It uses render arrays to define, display, validate, and process forms in a Drupal site.

Example form field definition:

 $form['name'] = [
   '#type' => 'textfield',
   '#title' => $this->t('Username'),
   '#size' => 60,
   '#maxlength' => UserInterface::USERNAME_MAX_LENGTH,
   '#description' => $this->t('Enter your @s username.', ['@s' => $config->get('name')]),
   '#required' => TRUE,
   '#attributes' => [
     'autocorrect' => 'none',
     'autocapitalize' => 'none',
     'spellcheck' => 'false',
     'autofocus' => 'autofocus',
   ],
 ];

Life cycle of a Drupal form

Form controllers centralize form logic, overseeing the form's journey from definition to processing. They are responsible for:

  1. Definition: Forms are defined as arrays, with the Form API providing a range of field types and properties to capture various kinds of input.
  2. Display: The Form API generates the HTML output for the form, handling field rendering, theme application, and client-side validation.
  3. Validation: Before processing submissions, the Form API validates input against defined criteria, safeguarding against invalid or malicious data.
  4. Submission and processing: Upon successful validation, the Form API processes the form, executing defined actions such as storing data or redirecting the user.

Read more about the life cycle of a form in Concept: Form Controllers and the Form Life Cycle.

Advantages of using the Form API

The benefits that you get from Drupal's Form API (FAPI) include:

  • Security: FAPI automatically applies security measures, such as CSRF tokens and input sanitization, reducing the risk of common vulnerabilities.
  • Reusability: Custom form components for complex widgets like a date picker or file upload field can be defined once and reused across multiple forms.
  • Extensibility: Forms can be altered by other modules through the use of hooks, allowing for one module to alter and enhance the forms provided by another.

This guide introduces the Form API and common use cases.

Learn more about advanced features of the Form API.

Recap

The Form API is essential for Drupal developers, enabling the creation of secure, user-friendly forms critical to site interaction and functionality.

Further your understanding

  • What do you think are the advantages of defining form fields as a $form array?
  • Consider the impact of the Form API on site security and developer productivity.

Additional resources

On this page

Drupal Module Developer Guide