builder property
final
Called to build the contents of this widget.
The builder can build different widgets depending on what is being dragged into this drag target.
onWillAccept or onWillAcceptWithDetails is called when a draggable
enters the target. If true, then the data will appear in candidateData,
else in rejectedData.
Typically the builder will check candidateData and rejectedData and
build a widget that indicates the result of dropping the candidateData
onto this target.
The candidateData and rejectedData are List types to support multiple
simultaneous drags.
If unexpected null values in candidateData or rejectedData, ensure
that the data argument of the Draggable is not null.
Implementation
final DragTargetBuilder<T> builder;