Listeners

Listeners are registered with a single call and run on both loaders. Register them from the common module's init() method so the subscription is active on both NeoForge and Fabric.

Registering a listener

Call register with an implementation of the listener interface. Because listener interfaces are functional interfaces, you almost always pass a lambda:

BlockEvent.BREAK.register((level, pos, state, player, xp) -> {
    System.out.println(player.getName().getString() + " broke a block at " + pos);
    return EventResult.pass();
});

The lambda's parameters match the listener method (breakBlock), and its return type matches too. Some events return nothing (void), some return an EventResult so you can influence the outcome.

Register your listeners during mod initialization - typically from the init() method in your common module, so the subscription applies on both loaders.

What your listener returns

The listener method's return type tells you whether you can affect the outcome:

• Some events return void - they're pure notifications. Every listener is called and none can cancel anything (for example, BlockEvent.FALLING_LAND).
• Some events return an EventResult - your listener can let the event continue or interrupt it and override the outcome, for example to cancel a block break.

The next page explains event results in detail.

note

If you create your own events for other code to listen to, see Creating Your Own Events.