Drupal 8: Creating a custom field - Part 2: Field drupal widget

This is part 2 in my series of articles about Drupal widgets, and specifically creating a custom field. I recommend reading Part 1: Field type first, if you have not done so already.

After creating the field type it is now time to create the field widget.

##a) Create the file
The field widget must be located as follows:
<module_name>/lib/Drupal/<module_name>/Plugin/field/widget/<field_widget_name>.php
N.B. The field widget name should be in CamelCase.

##b) Add Contains, namespace and use
In the newly created field type file add a brief comment to explain what it consists of:

/**
 * @file
 * Contains \Drupal\<module_name>\Plugin\field\widget\<field_widget_name>.
 */

N.B. The "Contains..." line should match the location and name of this file.

Then add the namespace as follows:

namespace Drupal\<module_name>\Plugin\field\widget;

N.B. I cannot emphasise enough: it is vital that the namespace matches the location of the file otherwise it will not work.

Then add the following uses:

use Drupal\Core\Entity\Field\FieldItemListInterface;

This provides a variable type required within the field widget class.

use Drupal\field\Plugin\Type\Widget\WidgetBase;

This provides the class that the field widget will extend.

##c) Add widget details annotation
The annotation should appear as follows:

/**
 * Plugin implementation of the '<field_widget_id>' widget.
 *
 * @FieldWidget(
 *   id = "<field_widget_id>",
 *   label = @Translation("<field_widget_label>"),
 *   field_types = {
 *     "<field_type_id>"
 *   }
 * )
 */

N.B. All text represented by a <placeholder> should be appropriately replaced according to requirements. The field_type_id must match the id of a field type and the field_widget_id should match the default widget specified in the field type (see Part 1 of this article).

##d) Add field widget class
Create the field widget class as follows:

class <field_widget_name> extends WidgetBase {

}

N.B. The <field_widget_name> must match the name of this file (case-sensitive).

The field widget class needs to contain the formElement() function that defines how the field will appear on data input forms:

 /**
   * {@inheritdoc}
   */
  public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, array &$form_state) {

    $element['forename'] = array(
      '#title' => t('Forename'),
      '#type' => 'textfield',
      '#default_value' => isset($items[$delta]->forename) ? $items[$delta]->forename : NULL,
    );
    $element['surname'] = array(
      '#title' => t('Surname'),
      '#type' => 'textfield',
      '#default_value' => isset($items[$delta]->surname) ? $items[$delta]->surname : NULL,
    );
    $element['age'] = array(
      '#title' => t('Age'),
      '#type' => 'number',
      '#default_value' => isset($items[$delta]->age) ? $items[$delta]->age : NULL,
    );
    return $element;
  }

The above example includes element types of textfield and number, other element types include:

• radios
• checkboxes
• email
• url

I intend to delve into other element types in a future article.

And there we have it: a complete (basic) field widget. Here is a simple example, similar to that described above.

Click Part 3: Field formatter to continue creating a custom field.