In the first article of the Drupal 8 Field API series, we saw how field formatters are written in Drupal 8. Now it’s time for widgets. You might get a déjà vu when reading as a lot resemble to formatters.
Plugins
Creating field widgets in Drupal 7 was done by implementing four hooks. In Drupal 8, widgets are now plugins using the new Plugin API. Hooks are replaced by methods in classes, which means that your module file will be empty if you only provide a widget, unless you also implement one of the (new) widget alter hooks. Being classes, this means that field widgets can now extend on each other. A good example in core is the image field widget extending the file field widget class. Discovery and class instantiation is managed by the new widget plugin manager.
Create a file like ‘{your_module}/lib/Drupal/{your_module}/Plugin/field/FieldWidget/{NameOfYourWidget}.php. That’s a lot of directories right ? Welcome to the world of PSR-0, namespaces and plugins in D8. This is most likely going to change, feel free to read, or even help along in https://drupal.org/node/1971198. Also, plugin managers can control where plugins reside, see https://drupal.org/node/2043379, so we’ll probably change this at some point.
In most cases, you will want to extend the WidgetBase class which does most of the heavy lifting for you (holds the code that was in the field_default_*() functions in Drupal 7). Following classes will usually be imported at the top of your file depending on which methods you override:
<?php
// WidgetBase class.
use Drupal\Core\Field\WidgetBase;
// FieldItemListInterface
use Drupal\Core\Field\FieldItemListInterface;
// Symfone violation interface
use Symfony\Component\Validator\ConstraintViolationInterface;
?>1. hook_field_widget_info() are now annotations
hook_field_widget_info() is replaced by annotation-based plugin discovery, using the \Drupal\field\Annotation\FieldWidget annotation class. As for other plugin types, the accepted properties are documented in the annotation class. Other modules can extend this by implementing hook_field_widget_info_alter(). Note that some property names have changed since Drupal 7 (spaces replaces by underscores). This is how an annotation looks like, which is placed right above the class keyword.
<?php
/**
* Plugin implementation of the 'foo_widget' widget
*
* @FieldWidget(
* id = "foo_widget",
* label = @Translation("Foo widget"),
* field_types = {
* "text",
* "text_long"
* },
* settings = {
* "size" = "600",
* }
* )
*/
class FooWidget extends WidgetBase { }
?>2. hook_field_widget_settings_form() becomes WidgetInterface::settingsForm()
Next up is to create a settingsForm() method. If you have an old settings form, you can simply move the code to this method. The calling code (typically Field UI) takes care of saving the settings on form submit. Remember to always start with an empty $elements array and not with the $form argument from the function arguments.
Side note: in all methods in the widget class:
- the settings values currently configured for the widget can be accessed with
$this->getSetting('settings_key'), or$this->getSettings() - the settings values currently configured for the field on which the widget is being used can be accessed with
$this->getSetting('settings_key'), or$this->getSettings(). Those methods return both field level settings and instance level settings, merged. - If access to field properties other than field settings is needed, the field definition can be accessed with
$this->getFieldDefinition(). This returns an object implementing \Drupal\Core\Entity\Field\FieldDefinitionInterface, which unifies the separate $field and $instance structures D7 coders are familiar with. More details on this will come in a following post.
<?php
/**
* {@inheritdoc}
*/
public function settingsForm(array $form, array &$form_state) {
$element = array();‘#type’ => ‘number’,
‘#title’ => t(‘Size of textfield’),
‘#default_value’ => $this->getSetting(‘size’),
‘#required’ => TRUE,
‘#min’ => 1,
);
}
?>
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