const DragTarget({Key key, @required DragTargetBuilder<T> builder, DragTargetWillAccept<T> onWillAccept, DragTargetAccept<T> onAccept })

Creates a widget that receives drags.

The builder argument must not be null.

Source 

const DragTarget({
  Key key,
  @required this.builder,
  this.onWillAccept,
  this.onAccept
}) : super(key: key);