hey.dart

 GroupedListView<NewMessageModel, String>(
                            elements: allMessages,
                            reverse: true,
                            controller: _scrollController,
                            groupBy: (element) =>
                                (element.createdAt ~/ 86400000).toString(),
                            groupSeparatorBuilder: (String groupByValue) => Row(
                              mainAxisAlignment: MainAxisAlignment.center,
                              children: [
                                Container(
                                  padding: EdgeInsets.symmetric(
                                      horizontal: 40.h, vertical: 10.h),
                                  decoration: BoxDecoration(
                                      color: AppColors.black,
                                      borderRadius: BorderRadius.circular(8)),
                                  child: regularText(
                                    DateFormat('MMMM dd, yyyy').format(
                                        DateTime.fromMillisecondsSinceEpoch(
                                            int.parse(groupByValue) * 86400000)),
                                    fontSize: 14,
                                    color: AppColors.white,
                                  ),
                                )
                              ],
                            ),
                            itemBuilder: (context, dynamic element) =>
                                MessageBubble(
                                  text: element.text,
                                  isSender: element.from == AppCache.getUser.uid,
                                  isRead: element.isRead,
                                  timeSent: DateFormat('hh:mm a').format(
                                      DateTime.fromMillisecondsSinceEpoch(
                                          element.createdAt)),
                                ),
                            itemComparator: (a,b) =>
                                a.createdAt.compareTo(b.createdAt),
                            useStickyGroupSeparators: true,
                            floatingHeader: true,
                            order: GroupedListOrder.DESC,
                          )