Machine Event Examples

Current API Minecraft 1.21.1 / MBD2 21.1.1

Events can select authored states; they do not create new states or renderers dynamically.

Empty-hand interaction and state changes

const InteractionResult = Java.loadClass('net.minecraft.world.InteractionResult')

MBDMachineEvents.onUseWithoutItem('example:crusher', wrapper => {
  const { machine, player } = wrapper.event
  const next = machine.machineStateName === 'idle' ? 'disabled' : 'idle'
  machine.setMachineState(next)
  player.sendSystemMessage(Component.literal(`Machine state: ${next}`))
  wrapper.event.setInteractionResult(InteractionResult.SUCCESS)
})

The state must already exist in the editor state machine. Unknown names are silently ignored.

Recipe lifecycle logging

MBDMachineEvents.onRecipeStatusChanged('example:crusher', wrapper => {
  const { machine, oldStatus, newStatus } = wrapper.event
  console.info(`${machine.pos}: ${oldStatus} -> ${newStatus}`)
})

MBDMachineEvents.onRecipeWorking('example:crusher', wrapper => {
  const { recipe, progress } = wrapper.event
  if (progress % 20 === 0) {
    console.debug(`${recipe.id}: ${progress}/${recipe.duration}`)
  }
})

Multiblock formation

MBDMachineEvents.onStructureFormed('example:blast_furnace', wrapper => {
  wrapper.event.machine.setMachineState('formed')
})

MBDMachineEvents.onStructureInvalid('example:blast_furnace', wrapper => {
  wrapper.event.machine.setMachineState('idle')
})

Block UI access and alter drops

MBDMachineEvents.onOpenUI('example:crusher', wrapper => {
  const { machine, player } = wrapper.event
  if (!player.hasPermissions(2) && machine.machineStateName === 'locked') {
    wrapper.event.setCanceled(true)
  }
})

MBDMachineEvents.onDrops('example:crusher', wrapper => {
  // drops is the underlying Java List<ItemStack>.
  wrapper.event.drops.add(Item.of('minecraft:iron_nugget', 3))
})

Placement, neighbors, and fuel

MBDMachineEvents.onPlaced('example:crusher', wrapper => {
  const { machine, itemStack } = wrapper.event
  const data = machine.customData.copy()
  data.putString('placed_from', `${itemStack.id}`)
  machine.setCustomData(data)
})

MBDMachineEvents.onNeighborChanged('example:crusher', wrapper => {
  console.debug(`Neighbor ${wrapper.event.block} changed at ${wrapper.event.fromPos}`)
})

MBDMachineEvents.onFuelRecipeModify('example:crusher', wrapper => {
  const fuelRecipe = wrapper.event.recipe
  console.debug(`Selected fuel: ${fuelRecipe.id}`)
})

Observe client synchronization

// kubejs/client_scripts/mbd2_visuals.js
MBDMachineEvents.onCustomDataUpdate('example:crusher', wrapper => {
  const { oldValue, newValue } = wrapper.event
  console.debug(`Client machine data changed: ${oldValue} -> ${newValue}`)
})

onClientTick and GeckoLib-only onCustomKeyframe are also client events; keep them visual-only.

Avoid world scans, JSON parsing, and UI reconstruction in onTick, onClientTick, and onRecipeWorking.

After a craft completes

MBDMachineEvents.onRecipeFinish('example:crusher', wrapper => {
  const { machine, recipe } = wrapper.event
  // The outputs already exist here; onAfterRecipeWorking runs before they do.
  console.info(`${recipe.id} finished at ${machine.pos}`)
})

MBDMachineEvents.onConsumeInputsAfterWorking('example:crusher', wrapper => {
  // Only fires when the machine defers input consumption to completion.
  console.debug(`deferred inputs taken for ${wrapper.event.recipe.id}`)
})

onFuelBurningFinish never fires

Its KubeJS name is registered, but MBDMachine#onFuelBurningFinish posts to the NeoForge bus without postCustomEvent(), so the handler is never called in 21.1.1. Watch machine.recipeLogic.fuelTime or the WAITING status instead.