ModifyTcaSelectFieldItemsEvent 

When it is dispatched 

Two item providers of this extension dispatch the event, after they added their own items to the ones the field declares:

The event is dispatched each time the backend form renders the field, not when the record is saved.

What this extension passes in 

getParameters() returns the parameters of the item provider, the ones TYPO3 hands an itemsProcFunc , and setParameters() replaces them. What a listener of these fields finds in them:

• table and field name the field. For a FlexForm field, table is tt_content and field the name of the FlexForm element, for example settings.showFields.
• items holds the items the field declares, followed by the ones of the provider. The shown fields offer profile.image, contracts.position, contracts.functionType, contracts.organisationalUnit, contracts.room, contracts.officeHours, contracts.physicalAddresses, contracts.emailAddresses, contracts.phoneNumbers and contracts.location, each in the group profile or contracts. The contract selects offer one item per contract, its uid as the value, sorted by the last and first name of the profile.
• The contract selects are already restricted to the storage folders page TSconfig names for the field, see Restrict the backend contract selects. A contract the record references is offered all the same.
• row is the record being edited, and for a FlexForm field the values of the FlexForm. flexParentDatabaseRow is the content element then.

In the backend form, TYPO3 v13 hands the static items of a field to the item provider as \TYPO3\CMS\Core\Schema\Struct\SelectItem objects, TYPO3 v14 as arrays, and the items a provider adds are arrays on both versions. A SelectItem implements \ArrayAccess , so a closure typed array|SelectItem that reads $item['value'] works on both.

Example 

A site does not show rooms, so editors are not offered the room in Show only selected Fields of the persons plugins:

<?php

declare(strict_types=1);

namespace MyVendor\MyExtension\EventListener;

use FGTCLB\AcademicBase\Event\ModifyTcaSelectFieldItemsEvent;
use TYPO3\CMS\Core\Attribute\AsEventListener;
use TYPO3\CMS\Core\Schema\Struct\SelectItem;

final class RemoveRoomFromShownFields
{
    #[AsEventListener(identifier: 'my-extension/remove-room-from-shown-fields')]
    public function __invoke(ModifyTcaSelectFieldItemsEvent $event): void
    {
        $parameters = $event->getParameters();
        if ($parameters['table'] !== 'tt_content' || $parameters['field'] !== 'settings.showFields') {
            return;
        }
        $parameters['items'] = array_values(array_filter(
            $parameters['items'],
            static fn(array|SelectItem $item): bool => ($item['value'] ?? null) !== 'contracts.room',
        ));
        $event->setParameters($parameters);
    }
}

Rules and pitfalls 

• Check the table and the field. The event is shared: the item providers of academic_jobs and academic_contacts4pages dispatch it as well, and the same listener is called for all of them.
• A value that is not among the items is lost on the next save. The fields of this page store plain values, so the backend form drops a stored value the listener removed from the items, and saving the record writes it away. Remove only items no record uses, or keep the ones the record in row references.
• The event decides what the backend offers. What the plugins render is decided by what the content element stored.

Introduced in 

• Feature: Dispatch ModifyTcaSelectFieldItemsEvent in itemsProcFunc handlers (2.4) made the item providers of this extension dispatch the event.
• Breaking: Renamed itemsProcFunc handler classes to FormEngine namespace (2.4) moved the item providers to the \Backend\FormEngine namespace.
• Feature: Restrict the backend contract selects (2.4) restricts the contract selects before the event.