events.md

---
title: Events
description: A guide for using events provided by the Fabric API.
authors:
  - dicedpixels
  - mkpoli
  - daomephsta
  - solidblock
  - draylar
  - jamieswhiteshirt
  - PhoenixVX
  - Juuxel
  - YanisBft
  - liach
  - natanfudge
authors-nogithub:
  - stormyfabric
---

# Events {#events}

Fabric API provides a system that allows mods to react to actions or occurrences, also defined as _events_ that occur in the game.

Events are hooks that satisfy common use cases and/or provide enhanced compatibility and performance between mods that hook into the same areas of the code. The use of events often substitutes the use of mixins.

Fabric API provides events for important areas in the Minecraft codebase that multiple modders may be interested in hooking into.

Events are represented by instances of `net.fabricmc.fabric.api.event.Event` which stores and calls _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 as well. For example, `ClientTickEvents` groups several related events together.

## Callbacks {#callbacks}

Callbacks are a piece of code that is passed as an argument to an event. When the event is triggered by the game, the passed piece of code will be executed.

### Callback Interfaces {#callback-interfaces}

Each event has a corresponding callback interface, conventionally named `<EventName>Callback`. Callbacks are registered by calling `register()` method 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.

## Listening to Events {#listening-to-events}

This example registers an `AttackBlockCallback` to damage the player when they hit blocks that don't drop an item when hand-mined.

@[code lang=java transcludeWith=:::1](@/reference/latest/src/main/java/com/example/docs/event/FabricDocsReferenceEvents.java)

### Adding Items to Existing Loot Tables {#adding-items-to-existing-loot-tables}

Sometimes you may want to add items to loot tables. For example, adding your drops to a vanilla block or entity.

The simplest solution, replacing the loot table file, can break other mods. What if they want to change them as well? We'll take a look at how you can add items to loot tables without overriding the table.

We'll be adding eggs to the coal ore loot table.

#### Listening to Loot Table Loading {#listening-to-loot-table-loading}

Fabric API has an event that is fired when loot tables are loaded, `LootTableEvents.MODIFY`. You can register a callback for it in your [mod's initializer](./getting-started/project-structure#entrypoints). Let's also check that the current loot table is the coal ore loot table.

@[code lang=java transclude={38-40}](@/reference/latest/src/main/java/com/example/docs/event/FabricDocsReferenceEvents.java)

#### Adding Items to the Loot Table {#adding-items-to-the-loot-table}

In loot tables, items are stored in _loot pool entries_, and entries are stored in _loot pools_. To add an item, we'll need to add a pool with an item entry to the loot table.

We can make a pool with `LootPool#builder`, and add it to the loot table.

Our pool doesn't have any items either, so we'll make an item entry using `ItemEntry#builder` and add it to the pool.

@[code highlight={6-7} transcludeWith=:::2](@/reference/latest/src/main/java/com/example/docs/event/FabricDocsReferenceEvents.java)

## Custom Events {#custom-events}

Some areas of the game do not have hooks provided by the Fabric API, so you can either use a mixin or create your own event.

We'll look at creating an event that is triggered when sheep are sheared. The process of creating an event is:

- Creating the event callback interface
- Triggering the event from a mixin
- Creating a test implementation

### Creating the Event Callback Interface {#creating-the-event-callback-interface}

The callback interface describes what must be implemented by event listeners that will listen to your event. The callback interface also describes how the event will be called from our mixin. It is conventional to place an `Event` object as a field in the callback interface, which will identify our actual event.

For our `Event` implementation, we will choose to use an array-backed event. The array will contain all event listeners that are listening to the event.

Our implementation will call the event listeners in order until one of them does not return `ActionResult.PASS`. This means that a listener can say "_cancel this_", "_approve this_" or "_don't care, leave it to the next event listener_" using its return value.

Using `ActionResult` as a return value is a conventional way to make event handlers cooperate in this fashion.

You'll need to create an interface that has an `Event` instance and method for response implementation. A basic setup for our sheep shear callback is:

@[code lang=java transcludeWith=:::](@/reference/latest/src/main/java/com/example/docs/event/SheepShearCallback.java)

Let's look at this more in-depth. When the invoker is called, we iterate over all listeners:

@[code lang=java transclude={21-22}](@/reference/latest/src/main/java/com/example/docs/event/SheepShearCallback.java)

We then call our method (in this case, `interact`) on the listener to get its response:

@[code lang=java transclude={33-33}](@/reference/latest/src/main/java/com/example/docs/event/SheepShearCallback.java)

If the listener says we have to cancel (`ActionResult.FAIL`) or fully finish (`ActionResult.SUCCESS`), the callback returns the result and finishes the loop. `ActionResult.PASS` moves on to the next listener, and in most cases should result in success if there are no more listeners registered:

@[code lang=java transclude={25-30}](@/reference/latest/src/main/java/com/example/docs/event/SheepShearCallback.java)

We can add Javadoc comments to the top of callback classes to document what each `ActionResult` does. In our case, it might be:

@[code lang=java transclude={9-16}](@/reference/latest/src/main/java/com/example/docs/event/SheepShearCallback.java)

### Triggering the Event From a Mixin {#triggering-the-event-from-a-mixin}

We now have the basic event skeleton, but we need to trigger it. Because we want to have the event called when a player attempts to shear a sheep, we call the event `invoker` in `SheepEntity#interactMob` when `sheared()` is called (i.e. sheep can be sheared, and the player is holding shears):

@[code lang=java transcludeWith=:::](@/reference/latest/src/main/java/com/example/docs/mixin/event/SheepEntityMixin.java)

### Creating a Test Implementation {#creating-a-test-implementation}

Now we need to test our event. You can register a listener in your initialization method (or another area, if you prefer) and add custom logic there. Here's an example that drops a diamond instead of wool at the sheep's feet:

@[code lang=java transcludeWith=:::3](@/reference/latest/src/main/java/com/example/docs/event/FabricDocsReferenceEvents.java)

If you enter into your game and shear a sheep, a diamond should drop instead of wool.