Nextcloud Syntax Events

nextcloud-syntax-events

Quick Reference

Core Interfaces

IEventDispatcher Methods

IEventListener Interface

interface IEventListener {
    public function handle(Event $event): void;
}

Event Naming Conventions

ALWAYS end event class names with Event.

Frontend Event Bus (@nextcloud/event-bus)

Frontend event naming convention: app-id:object:verb (e.g., files:node:uploaded)

Critical Warnings

NEVER use deprecated hooks ($userManager->listen(...)) -- ALWAYS use typed events with IEventDispatcher or IRegistrationContext::registerEventListener().

NEVER use GenericEvent -- deprecated since NC 22. ALWAYS create typed event classes extending OCP\EventDispatcher\Event.

NEVER skip the instanceof check in handle() -- the interface types the parameter as base Event, not your specific event class.

NEVER dispatch events in constructors -- services may not be fully initialized during construction.

NEVER forget to call parent::__construct() in custom event classes.

NEVER register event listeners in boot() -- ALWAYS use register() method via IRegistrationContext::registerEventListener() for lazy resolution.

ALWAYS register listeners via IRegistrationContext::registerEventListener() in Application::register() -- this is the recommended NC 28+ approach.

ALWAYS use dispatchTyped() for dispatching events -- NEVER use string-based event names with typed event objects.

ALWAYS use @nextcloud/event-bus for frontend cross-component communication -- NEVER use custom DOM events or global variables.

ALWAYS unsubscribe frontend event handlers when the component is destroyed -- failure to do so causes memory leaks.

Decision Tree: Choosing Your Event Pattern

Need to react to something happening in Nextcloud?
|
+-- Is it a PHP backend event?
|   |
|   +-- Is there a built-in event for this? (see references/methods.md)
|   |   |
|   |   +-- YES --> Register listener for that event class
|   |   +-- NO  --> Create a custom event class extending Event
|   |
|   +-- How to register the listener?
|       |
|       +-- In an app (recommended) --> IRegistrationContext::registerEventListener()
|       +-- Quick inline logic        --> IEventDispatcher::addListener() with closure
|       +-- DI-resolved class         --> IEventDispatcher::addServiceListener()
|
+-- Is it a frontend (JavaScript/TypeScript) event?
    |
    +-- Cross-component communication --> @nextcloud/event-bus (subscribe/emit)
    +-- Reacting to Files app actions --> subscribe to 'files:node:*' events

Essential Patterns

Pattern 1: Register a Listener in Application (Recommended)

namespace OCA\MyApp\AppInfo;

use OCA\MyApp\Listener\NodeCreatedListener;
use OCP\AppFramework\App;
use OCP\AppFramework\Bootstrap\IBootstrap;
use OCP\AppFramework\Bootstrap\IBootContext;
use OCP\AppFramework\Bootstrap\IRegistrationContext;
use OCP\Files\Events\Node\NodeCreatedEvent;

class Application extends App implements IBootstrap {
    public const APP_ID = 'myapp';

    public function __construct() {
        parent::__construct(self::APP_ID);
    }

    public function register(IRegistrationContext $context): void {
        $context->registerEventListener(
            NodeCreatedEvent::class,
            NodeCreatedListener::class
        );
    }

    public function boot(IBootContext $context): void {
    }
}

Pattern 2: Implement IEventListener

namespace OCA\MyApp\Listener;

use OCP\EventDispatcher\Event;
use OCP\EventDispatcher\IEventListener;
use OCP\Files\Events\Node\NodeCreatedEvent;
use Psr\Log\LoggerInterface;

class NodeCreatedListener implements IEventListener {
    public function __construct(
        private LoggerInterface $logger,
    ) {
    }

    public function handle(Event $event): void {
        if (!($event instanceof NodeCreatedEvent)) {
            return;
        }

        $node = $event->getNode();
        $this->logger->info('File created: ' . $node->getPath());
    }
}

Pattern 3: Create and Dispatch a Custom Event

// lib/Event/ItemCreatedEvent.php
namespace OCA\MyApp\Event;

use OCP\EventDispatcher\Event;

class ItemCreatedEvent extends Event {
    public function __construct(
        private string $itemId,
        private string $userId,
        private array $data,
    ) {
        parent::__construct();
    }

    public function getItemId(): string {
        return $this->itemId;
    }

    public function getUserId(): string {
        return $this->userId;
    }

    public function getData(): array {
        return $this->data;
    }
}

// lib/Service/ItemService.php
namespace OCA\MyApp\Service;

use OCA\MyApp\Event\ItemCreatedEvent;
use OCP\EventDispatcher\IEventDispatcher;

class ItemService {
    public function __construct(
        private IEventDispatcher $dispatcher,
    ) {
    }

    public function createItem(string $userId, array $data): void {
        // ... create the item ...

        $this->dispatcher->dispatchTyped(
            new ItemCreatedEvent($itemId, $userId, $data)
        );
    }
}

Pattern 4: Inline Callback Listener (Simple Cases Only)

use OCP\EventDispatcher\IEventDispatcher;
use OCP\Files\Events\Node\NodeDeletedEvent;

$dispatcher = $container->get(IEventDispatcher::class);
$dispatcher->addListener(
    NodeDeletedEvent::class,
    function (NodeDeletedEvent $event) {
        // Quick inline handling
        $path = $event->getNode()->getPath();
    }
);

Pattern 5: Frontend Event Bus

import { emit, subscribe, unsubscribe } from '@nextcloud/event-bus'

// Subscribe to a built-in event
const handler = (node: Node) => {
    console.log('File uploaded:', node.path)
}
subscribe('files:node:uploaded', handler)

// Emit a custom event
emit('myapp:item:created', { id: 42, name: 'New Item' })

// ALWAYS unsubscribe on component teardown
// In Vue Options API:
beforeDestroy() {
    unsubscribe('files:node:uploaded', handler)
}

// In Vue Composition API:
onBeforeUnmount(() => {
    unsubscribe('files:node:uploaded', handler)
})

Pattern 6: TypeScript Typed Frontend Events

// In a .d.ts file (e.g., src/events.d.ts)
declare module '@nextcloud/event-bus' {
    interface NextcloudEvents {
        'myapp:item:created': { id: number; name: string }
        'myapp:item:deleted': { id: number }
        'myapp:settings:changed': { key: string; value: unknown }
    }
}
export {}

// Usage -- TypeScript infers event payload types automatically
subscribe('myapp:item:created', (event) => {
    console.log(event.id)   // TypeScript knows: number
    console.log(event.name) // TypeScript knows: string
})

emit('myapp:item:created', { id: 1, name: 'Test' })

Built-In Events (Summary)

See references/methods.md for the complete catalog.

Reference Links

• references/methods.md -- Complete built-in events catalog, IEventDispatcher API, IEventListener interface
• references/examples.md -- Custom events, listeners, dispatching, frontend event-bus patterns
• references/anti-patterns.md -- Common event system mistakes

Official Sources

• https://docs.nextcloud.com/server/latest/developer_manual/basics/events.html
• https://github.com/nextcloud-libraries/nextcloud-event-bus