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Documentation Index

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Create fires NeoForge bus events at key lifecycle points so that addon mods can observe and extend its behaviour without modifying internal classes. All events in com.simibubi.create.api.event are stable public API and are posted on the NeoForge event bus (not the mod bus).

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BlockEntityBehaviourEvent

com.simibubi.create.api.event.BlockEntityBehaviourEvent This event fires just before a SmartBlockEntity is deserialised from NBT, and also when a fresh block entity is placed in the world. Use it to attach a new BlockEntityBehaviour to any of Create’s smart block entities, or to replace an existing one. Because the event fires before NBT is read, any behaviours you attach here will have full access to the block entity’s saved data through BlockEntityBehaviour#read().

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Methods

MethodDescription
forType(BlockEntityType<T> type, Consumer<T> action)Run action only if the block entity matches type. Safely casts the entity for you.
attach(BlockEntityBehaviour behaviour)Add (or replace) a behaviour on the block entity, keyed by behaviour.getType().
remove(BehaviourType<?> type)Remove a previously registered behaviour of the given type, returning it.

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Example

// Subscribe on the NeoForge event bus:
neoForgeEventBus.addListener((BlockEntityBehaviourEvent event) -> {
    event.forType(AllBlockEntityTypes.FUNNEL.get(), be -> {
        event.attach(new FunFunnelBehaviour(be));
    });
});
Behaviours attached via this event are available during BlockEntityBehaviour#initialize() and have access to the initial NBT during BlockEntityBehaviour#read(). If the block entity was just placed (not loaded from disk), blockEntityData will be empty.
Use event.remove(SomeBehaviourType.TYPE) with caution — removing a behaviour that Create relies on internally can cause unexpected crashes or block entity failures.

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PipeCollisionEvent

com.simibubi.create.api.event.PipeCollisionEvent This event fires when two fluids meet inside a pipe network or when a pipe fluid encounters a fluid already present in the world. By default, Create produces cobblestone (water + lava) or obsidian, but you can override the result for any fluid combination. The event has two subtypes:

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PipeCollisionEvent.Flow

Fires when two fluids collide inside a pipe (both are flowing through the network). 
neoForgeEventBus.addListener((PipeCollisionEvent.Flow event) -> {
    Fluid first = event.getFirstFluid();
    Fluid second = event.getSecondFluid();
    Level level = event.getLevel();
    BlockPos pos = event.getPos();

    // Override the result block placed at the collision point
    if (first == Fluids.WATER && second == MyFluids.ACID.get()) {
        event.setState(Blocks.GLASS.defaultBlockState());
    }
});
MethodDescription
getFirstFluid()The first fluid in the collision
getSecondFluid()The second fluid in the collision
getLevel()The world in which the collision occurs
getPos()The block position of the collision
getState()The current result BlockState to be placed (may be null)
setState(BlockState)Override the block placed at the collision point; pass null to place nothing

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PipeCollisionEvent.Spill

Fires when a pipe fluid meets a fluid already present in the world (e.g., a pipe opening into a lava lake). 
neoForgeEventBus.addListener((PipeCollisionEvent.Spill event) -> {
    Fluid worldFluid = event.getWorldFluid();
    Fluid pipeFluid = event.getPipeFluid();
    // Suppress cobblestone formation for a specific combination
    if (worldFluid == MyFluids.COOLANT.get()) {
        event.setState(null);
    }
});
MethodDescription
getWorldFluid()The fluid already present in the world
getPipeFluid()The fluid travelling through the pipe
getLevel()The world in which the spill occurs
getPos()The block position of the spill
getState() / setState(BlockState)Get or override the result block
If setState(null) is called (or if no subscriber sets a state), no block is placed and the event produces no world change.

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TrackGraphMergeEvent

com.simibubi.create.api.event.TrackGraphMergeEvent Fires when two separate train track networks (TrackGraph instances) are connected — for example, when a player lays a rail that bridges a gap between two existing networks. Create merges the smaller graph into the larger one and fires this event immediately after. This is particularly useful for addon mods that maintain per-network state (e.g., a custom train scheduling system that stores data per-graph UUID).

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Methods

MethodDescription
getGraphMergedInto()The surviving TrackGraph that absorbed the other
getGraphMergedFrom()The TrackGraph that was merged away (it will no longer be active after this event)

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Example

neoForgeEventBus.addListener((TrackGraphMergeEvent event) -> {
    TrackGraph surviving = event.getGraphMergedInto();
    TrackGraph dissolved = event.getGraphMergedFrom();

    // Migrate any addon state keyed by graph ID
    MyAddonData.migrateGraph(dissolved.id, surviving.id);
});
The mergedFrom graph is effectively destroyed after this event. Do not retain strong references to it — use getGraphMergedInto() going forward for any network-level operations.

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Subscribing to events

All three events are posted on the NeoForge event bus, not the mod-loading bus. Use either the annotation approach or the programmatic approach: 
// Option A — annotation-based (static methods)
// @EventBusSubscriber defaults to the NeoForge game event bus
@EventBusSubscriber(modid = "mymod")
public class MyEventHandlers {
    @SubscribeEvent
    public static void onBehaviourEvent(BlockEntityBehaviourEvent event) {
        // ...
    }
}

// Option B — programmatic (instance methods, registered in mod constructor)
NeoForge.EVENT_BUS.addListener(this::onBehaviourEvent);
Events in com.simibubi.create.api.event are stable public API. Events in other Create packages (such as com.simibubi.create.content) are internal and may be removed or changed without notice.

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