data_grid_jank_example

main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.light(
        useMaterial3: true,
      ),
      darkTheme: ThemeData.dark(
        useMaterial3: true,
      ),
      themeMode: ThemeMode.system,
      home: const Home(),
    );
  }
}

class Home extends StatefulWidget {
  const Home({Key? key}) : super(key: key);

  @override
  State<Home> createState() => _HomeState();
}

const int pages = 10000;

class _HomeState extends State<Home> {
  late PageController _controller;

  // This points always to the mid-element in _list
  late int _initialIndex;

  @override
  void initState() {
    super.initState();
    // Calculate mid.
    _controller =
        PageController(initialPage: pages ~/ 2, viewportFraction: 1);
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  List months = [
    'jan',
    'feb',
    'mar',
    'apr',
    'may',
    'jun',
    'jul',
    'aug',
    'sep',
    'oct',
    'nov',
    'dec'
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        elevation: 2,
        title: const Text("Data Grid"),
      ),
      body: PageView.builder(
          controller: _controller,
          itemCount: pages,
          itemBuilder: (BuildContext context, int index) {
            int relIndex = index - (pages ~/ 2);
            return Column(
              children: [
                Text(months[DateTime(2022, 8 + relIndex, 1).month - 1] +
                    " " +
                    DateTime(2022, 8 + relIndex, 1).year.toString()),
                GridView.builder(
                  gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(
                    childAspectRatio: 1,
                    crossAxisCount: 7,
                    mainAxisExtent: 40,
                  ),
                  itemCount: 42,
                  physics: const NeverScrollableScrollPhysics(),
                  shrinkWrap: true,
                  itemBuilder: (context, i) {
                    return DataWidget(
                      dataIndex: getDatesForACalendarMonthAsUTC(
                          dateTime: DateTime(2022, 8 + relIndex, 1))[i],
                      gridIndex: DateTime(2022, 8 + relIndex, 1),
                    );
                  },
                ),
              ],
            );
          }),
    );
  }
}

class DataWidget extends StatelessWidget {
  const DataWidget({Key? key, required this.dataIndex, required this.gridIndex})
      : super(key: key);

  final DateTime dataIndex;
  final DateTime gridIndex;

  @override
  Widget build(BuildContext context) {
    return Row(
      children: [
        const Expanded(
          child: SizedBox(),
        ),
        OutlinedButton(
          style: OutlinedButton.styleFrom(
            minimumSize: Size.zero,
            padding: EdgeInsets.zero,
            foregroundColor: Theme.of(context).colorScheme.onSurface,
            tapTargetSize: MaterialTapTargetSize.shrinkWrap,
            side: BorderSide.none,
            shape: const RoundedRectangleBorder(
              borderRadius: BorderRadius.all(Radius.circular(12)),
            ),
          ).copyWith(elevation: ButtonStyleButton.allOrNull(0.0)),
          onPressed: dataIndex.month == gridIndex.month
              ? () {
                  //do something
                }
              : null,
          child: SizedBox(
            width: 40,
            child: Container(
              margin: const EdgeInsets.all(4.0),
              child: Ink(
                decoration: BoxDecoration(
                  border: Border.all(
                      color: Theme.of(context).dividerColor, width: 1),
                  borderRadius: const BorderRadius.all(Radius.circular(12)),
                ),
                child: Center(
                  child: Text(
                    dataIndex.day.toString(),
                    style: const TextStyle(),
                  ),
                ),
              ),
            ),
          ),
        ),
        const Expanded(
          child: SizedBox(),
        ),
      ],
    );
  }
}

List<DateTime> getDatesForACalendarMonthAsUTC({required DateTime dateTime}) {
  List<DateTime> calendarMonthDaysAsUTC = [];

  DateTime currentDateTime = DateTime.utc(dateTime.year, dateTime.month, 1);

  DateTime firstDayOfMonthAsUTC =
      DateTime.utc(currentDateTime.year, currentDateTime.month, 1);
  DateTime lastDayOfMonthAsUTC =
      getLastDayOfAMonth(currentDateTime: currentDateTime);

  List<DateTime> datesFirstToLastDayOfMonthAsUTC =
      getDaysInBetweenIncludingStartEndDate(
          startDateTime: firstDayOfMonthAsUTC,
          endDateTime: lastDayOfMonthAsUTC);

  calendarMonthDaysAsUTC = List.generate(datesFirstToLastDayOfMonthAsUTC.length,
      (index) => datesFirstToLastDayOfMonthAsUTC[index]);

  int firstDayOfMonthWeekDay = firstDayOfMonthAsUTC.weekday;

  for (int i = 1;
      i <= firstDayOfMonthWeekDay && firstDayOfMonthWeekDay != 7;
      i++) {
    calendarMonthDaysAsUTC.insert(
        0, firstDayOfMonthAsUTC.subtract(Duration(days: i)));
  }

  int daysLeftAfterMonthEndDate = 42 - calendarMonthDaysAsUTC.length;

  for (int i = 1; i <= daysLeftAfterMonthEndDate; i++) {
    calendarMonthDaysAsUTC.add(lastDayOfMonthAsUTC.add(Duration(days: i)));
  }

  return calendarMonthDaysAsUTC;
}

List<DateTime> getDaysInBetweenIncludingStartEndDate(
    {required DateTime startDateTime, required DateTime endDateTime}) {
  // Converting dates provided to UTC
  // So that all things like DST don't affect subtraction and addition on dates
  DateTime startDateInUTC =
      DateTime.utc(startDateTime.year, startDateTime.month, startDateTime.day);
  DateTime endDateInUTC =
      DateTime.utc(endDateTime.year, endDateTime.month, endDateTime.day);

  // Created a list to hold all dates
  List<DateTime> daysInFormat = [];

  // Starting a loop with the initial value as the Start Date
  // With an increment of 1 day on each loop
  // With condition current value of loop is smaller than or same as end date
  for (DateTime i = startDateInUTC;
      i.isBefore(endDateInUTC) || i.isAtSameMomentAs(endDateInUTC);
      i = i.add(const Duration(days: 1))) {
    // Converting back UTC date to Local date before inserting in list
    // You can keep in UTC format depending on your case

    if (startDateTime.isUtc) {
      daysInFormat.add(i);
    } else {
      daysInFormat.add(DateTime(i.year, i.month, i.day));
    }
  }
  return daysInFormat;
}

DateTime getLastDayOfAMonth({required DateTime currentDateTime}) {
  // Getting the 15th-day date of the month for the date provided
  DateTime fifteenthDayOfMonth =
      DateTime(currentDateTime.year, currentDateTime.month, 15);

  // Converting the 15th-day date to UTC
  // So that all things like DST don't affect subtraction and addition on date
  DateTime twentiethDayOfMonthInUTC = fifteenthDayOfMonth.toUtc();

  // Getting a random date of next month by adding 20 days to twentiethDayOfMonthInUTC
  // Adding number 20 to any month 15th-day will definitely give a next month date
  DateTime nextMonthRandomDateInUTC =
      twentiethDayOfMonthInUTC.add(const Duration(days: 20));

  DateTime nextMonthRandomDateZeroDayInUTC = DateTime.utc(
      nextMonthRandomDateInUTC.year, nextMonthRandomDateInUTC.month, 0);

  // Now getting the 0th day date of the next month
  // This will give us the current month last date
  DateTime nextMonthRandomDateZeroDayInLocal = DateTime(
      nextMonthRandomDateInUTC.year, nextMonthRandomDateInUTC.month, 0);

  DateTime lastDayOfAMonth;
  if (currentDateTime.isUtc) {
    lastDayOfAMonth = nextMonthRandomDateZeroDayInUTC;
  } else {
    lastDayOfAMonth = nextMonthRandomDateZeroDayInLocal;
  }

  return lastDayOfAMonth;
}