main.dart

DragTarget(
              builder: (context, List<String> candidateData, rejectedData) {
                return Center(
                  child: isSuccessful
                      ? Padding(
                          padding: EdgeInsets.only(top: 100.0),
                          child: Container(
                            color: Colors.yellow,
                            height: 200.0,
                            width: 200.0,
                            child: Center(
                                child: FlutterLogo(
                              size: 100.0,
                            )),
                          ),
                        )
                      : Container(
                          height: 200.0,
                          width: 200.0,
                          color: Colors.yellow,
                        ),
                );
              },
              onWillAccept: (data) {
                return true;
              },
              onAccept: (data) {
                setState(() {
                  isSuccessful = true;
                });
              },
            ),