Start a drag from a widget

Request drag detection

DetectDragIfPressed examines the supplied pointer event and prepares a drag-detection reply when the chosen key is pressed. Call it from OnMouseButtonDown and return its FEventReply. Choose the widget that should detect the drag; the Blueprint helper normally defaults that target to the current widget.

OnMouseButtonDown(MouseEvent)
  Reply = Detect Drag if Pressed(
    Pointer Event: MouseEvent,
    Drag Key: Left Mouse Button
  )
  Return Reply

Create the operation when dragging starts

OnDragDetected supplies an Operation output. Create the desired DragDropOperation and return it through that output. For the inventory example, set its item data and source-slot information, and give it a separate preview widget.

Debug the handoff

Check the two stages separately: confirm that the mouse override receives the press, then confirm that OnDragDetected runs. A button inside your item widget can change which element handles the press, so inspect the actual input path in your widget hierarchy.