Events Reference

Global drag / drop / auto-transfer / swap events live in UDNDEvents. Content-change events for a specific inventory live in UniversalInventory.

Short Version

If you need to...	Listen to
Know when the player starts or ends a drag	`UDNDEvents.OnDragStarted`, `UDNDEvents.OnDragEnded`
React to a successful drop	`UDNDEvents.OnDropCompleted`
Show a cancellation reason	`UDNDEvents.OnDragCancelled`
Track quick-click transfer	`UDNDEvents.OnAutoTransferCompleted`, `UDNDEvents.OnAutoTransferFailed`
Track inventory content changes	`UniversalInventory.OnItemAdded`, `UniversalInventory.OnItemRemoved`
Block swap before it runs	`UDNDEvents.OnSwapAttempting`

Normal Drag / Drop

Typical successful order:

OnDragAttempting
OnDragStarted
OnDragEnterSlot / OnDragExitSlot while hovering
OnDropAttempting
OnDropCompleted
OnDragEnded

If drag or drop is cancelled, OnDragCancelled runs instead of OnDropCompleted, and OnDragEnded still runs after it.

OnDragEnded is the safest place for cleaning up temporary UI because it runs at the end of both successful and failed flows.

Global Events (`UDNDEvents`)

These are static events. Subscribe with UDNDEvents.OnX += handler; unsubscribe in OnDisable or another teardown method.

DragAndDropManager clears subscribers from the previous Play session at the start of a new Play session. This matters for Fast Enter Play Mode.

Drag

Event	When it runs	Note
`OnDragAttempting`	Before drag starts	Rules can cancel the operation
`OnDragStarted`	Drag is confirmed	`DragContext` is available
`OnDragEnterSlot`	Pointer enters a slot	Useful for hover UI
`OnDragExitSlot`	Pointer leaves a slot	Useful for clearing hover UI
`OnDropAttempting`	Before drop processing	Target is already known
`OnDropCompleted`	Drop succeeded	Changes are already applied
`OnDragCancelled`	Drag or drop was cancelled	Use for error messages or UI cleanup
`OnDragStackChanged`	Drag stack amount changed	For example after split drop
`OnDragEnded`	Drag cycle ended	Always runs at the end

Auto-Transfer

Event	When it runs
`OnAutoTransferAttempting`	Before quick-click transfer
`OnAutoTransferCompleted`	Quick-click transfer succeeded
`OnAutoTransferFailed`	Quick-click transfer failed

Swap

Event	When it runs	Note
`OnSwapAttempting`	Before swap	Set `Cancel = true` to block swap
`OnSwapCompleted`	Swap succeeded	Slots already contain the resulting stacks

Inventory Events

UniversalInventory sends events when its content actually changed.

Event	When it runs	Context
`OnItemAdded`	Item was added to the inventory	`InventoryItemEventContext`
`OnItemRemoved`	Item was removed from the inventory	`InventoryItemEventContext`

`InventoryItemEventContext` Fields

Field	Type	Description
`Stack`	`ItemStack`	Stack that was added or removed
`SlotIndex`	`int`	Slot index
`SourceInventory`	`IInventory`	Where the item came from, if known
`TargetInventory`	`IInventory`	Where the item went, if known
`SourceSlot`	`BaseSlot`	Source slot, if known
`TargetSlot`	`BaseSlot`	Target slot, if known

In practice:

context.Stack.PrimaryAdapter gives the main item adapter
context.Stack.Count gives the amount
for transfers between different inventory types, remove usually contains the item before conversion, and add contains the item after conversion

Swap Context

`InventorySwapContext` Fields

Field	Type	Description
`SourceStack`	`ItemStack`	Stack in the source slot before swap
`TargetStack`	`ItemStack`	Stack in the target slot before swap
`SourceSlot`	`BaseSlot`	Slot where dragging started
`TargetSlot`	`BaseSlot`	Slot where the item was dropped
`SourceInventory`	`IInventory`	Source inventory
`TargetInventory`	`IInventory`	Target inventory
`Cancel`	`bool`	Set `true` to cancel swap

For swap between different inventory types, the final adapter objects in slots may differ from the ones in SourceStack and TargetStack before execution. That is expected: items are converted for the target inventory.

When Events Are Sent

Events are sent only after the inventory was changed successfully.

If transfer validation fails, there is no space, or the operation is cancelled, add/remove events are not sent. Subscribers do not see temporary state that the system later rolled back.

For group transfer, each item is processed separately:

a successful item sends its own events
a failed item stays where it was and sends no events
failure of one item does not cancel events from items that were already transferred successfully