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Getting Started with Forms in Drupal 8

Form basics

There are two key elements to crafting forms.  The workflow a form goes through, including how Drupal locates the form to display on a page, handling validation when someone submits a form, and ultimately doing something with the collected data. And the definition of the form itself, in which one determines if your form will have checkboxes, textfields, upload widgets, and/or any user-facing text.

Form definition

The way that forms are defined in Drupal hasn’t changed that much between Drupal 7 and Drupal 8, and I’m not going to go into too much detail here. Form definitions are still a Drupal render array made up of Form API elements that are ultimately parsed down to the HTML that is presented to the browser. The biggest change to crafting forms is the addition of some new HTML5 elements that can be defined in the Form API array, like tel number date.

Watch our Drupal 7 Module Developement series for a few lessons about using the Form API and form arrays in Drupal 7.

Form workflow

Truth be told, form workflow hasn’t changed that much at a high level  either. We still have the concepts of building, validation, and submission. And they’re still all available for us to hook into by simply conforming to a specific pattern. It’s really just the pattern that has changed. So lets take a look at that.

With the move to more modern PHP usage and Object Oriented Progamming patterns in Drupal 8,  we now have the concept of form objects defined by a form class. All form classes implement the Drupal\Core\Form\FormInterface interface, which states that any form object should have getFormId, buildForm, validateForm, and submitForm methods. It turns out that this matches up nicely with the build, validate, and submit workflow. By conforming to this interface, we ensure that Drupal knows how to process each step of the workflow for the form in question, given any form object. Before we look at some sample code, however, lets talk just a little bit more about a typical form workflow.

When a user visits a URL on a site,  /contact for example, Drupal needs to return the HTML representation of the required form so that it can be displayed in the user’s browser. In order to get that form definition, Drupal loads the required form object. Then Drupal calls the buildForm() method on that object. This returns a Form API array that Drupal can turn into HTML. Likely this HTML includes also a button that a user can click. Clicking the button generates an HTTP Post request to the URL defined as the action of the form. In Drupal, this is the same URl in which the form is displayed (i.e., /contact).

Once you know how it works, the entire process is actually quite simple and beautiful. And it hasn’t changed all that much, even since the Drupal 4.7 era. Many people love to hate it, but it’s easy to argue that Form API is one of the strongest features in Drupal.

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