How to Build Multi-step Forms in Drupal 8

This article demonstrates building a multi-step form in Drupal 8 using two separate forms and Drupal's core temporary data storage. Let's streamline the explanation and improve the flow.

Key Concepts:

• Two Independent Forms: The multi-step form is constructed from two distinct forms, each handling a subset of the user input.
• Abstract Base Class (MultistepFormBase): Common functionality, such as dependency injection, form scaffolding, and data processing, is centralized in an abstract base class. This promotes code reusability and maintainability.
• PrivateTempStore: Drupal's PrivateTempStore ensures data persistence across multiple requests, enabling the multi-step process.
• Route Definitions: Separate routes are defined for each form, allowing navigation between steps.

Implementation Details:

The solution involves:

1. MultistepFormBase.php: This abstract base class handles common tasks:

   • Dependency Injection: Injects PrivateTempStoreFactory, SessionManagerInterface, and AccountInterface.
   • Session Management: Ensures a session exists for anonymous users.
   • Data Storage: Uses PrivateTempStore to store form data (multistep_data key).
   • Data Saving (saveData()): A placeholder for the actual data saving logic (implementation depends on your specific needs).
   • Data Deletion (deleteStore()): Removes stored data after successful submission.

2. MultistepOneForm.php: The first form:

   • Extends MultistepFormBase.
   • Contains two fields: name and email.
   • Retrieves previously entered values from PrivateTempStore for pre-population.
   • Redirects to demo.multistep_two upon submission.

3. MultistepTwoForm.php: The second form:

   • Extends MultistepFormBase.
   • Contains two fields: age and location.
   • Retrieves previously entered values from PrivateTempStore.
   • Includes a "Previous" link redirecting to demo.multistep_one.
   • Calls saveData() from the base class upon submission and then redirects.

4. demo.routing.yml: Defines routes for demo.multistep_one and demo.multistep_two, associating them with the respective form classes.

Illustrative Screenshots:

Code Snippets (Illustrative):

(MultistepFormBase.php - Excerpt):

protected function saveData() {
  //  Save data (e.g., create a configuration entity)
  $this->deleteStore();
  drupal_set_message($this->t('Form saved!'));
}

(MultistepOneForm.php - Excerpt):

$form['name'] = [
  '#type' => 'textfield',
  '#title' => $this->t('Your name'),
  '#default_value' => $this->store->get('name') ?: '',
];

Conclusion:

This approach provides a clean and efficient way to create multi-step forms in Drupal 8, leveraging the power of the PrivateTempStore for cross-request data management. The use of an abstract base class promotes code organization and reusability. This structure can easily be extended to accommodate more steps. The FAQ section is omitted here for brevity, as the article body already covers the essential aspects.

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