In this tutorial you will learn to:

1. Understand Events and Callbacks
2. Register a callback for an existing Event

Events are represented by instances of net.fabricmc.fabric.api.event.Event which store and call callbacks. Often there is a single event instance for a callback, which is stored in a static field EVENT of the callback interface, but there are other patterns. For example ClientTickEvents groups several related events together.

Each event has a corresponding callback interface, conventionally named EventNameCallback. Callbacks are registered by calling register() on an event instance with an instance of the callback interface as the argument.

All event callback interfaces provided by Fabric API can be found in the net.fabricmc.fabric.api.event package. A partial list of existing callbacks is provided at the bottom of this tutorial.

Although there are plenty of events already provided by Fabric API, you can still make your own events. Please refer to events.

This example registers an AttackBlockCallback to damage players when they hit blocks that don't drop when hand-mined. It returns ActionResult.PASS as other callbacks should still be called. See the AttackBlockCallback JavaDoc in your IDE for the meaning of other values.

public class ExampleMod implements ModInitializer
{
    [...]
 
    @Override
    public void onInitialize() 
    {
        AttackBlockCallback.EVENT.register((player, world, hand, pos, direction) -> 
        {
            BlockState state = world.getBlockState(pos);
            /* Manual spectator check is necessary because AttackBlockCallbacks
               fire before the spectator check */
            if (state.isToolRequired() && !player.isSpectator() && 
                player.getMainHandStack().isEmpty()) 
            {
                player.damage(DamageSource.GENERIC, 1.0F);
            } 
            return ActionResult.PASS;
        });
    }
}

Player: AttackBlockCallback / AttackEntityCallback / UseBlockCallback / UseEntityCallback / UseItemCallback

Player (Client): ClientPickBlockApplyCallback / ClientPickBlockCallback / ClientPickBlockGatherCallback

BlockConstructedCallback / ItemConstructedCallback

RegistryEntryAddedCallback / RegistryEntryRemovedCallback / RegistryIdRemapCallback

LootTableLoadingCallback

There is an example of using LootTableLoadingCallback here.

WorldTickCallback

ServerStartCallback / ServerStopCallback / ServerTickCallback

C2SPacketTypeCallback / S2CPacketTypeCallback