View

https://pub.dev/packages/table_calendar

import 'package:table_calendar/table_calendar.dart';

...

CalendarController _calendarController = CalendarController();
Map<DateTime, List<EventsModel>> _events;
DateTime _selectedDay;

...

  Widget _buildCalendarCustom() {
    return TableCalendar(
      locale: 'ko-KR',
      calendarController: _calendarController,
      events: _events,
      availableGestures: AvailableGestures.all,
      onDaySelected: _onDaySelected,
      builders: calendarBuilder(),
      headerVisible: false,
    );
  }

  void _onDaySelected(DateTime day, List e) {
    setState(() {
      _selectedDay = day;
      e.length == 0 ? _selectedEvents = [] : _selectedEvents = e;
    });
  }

Calendar Builders

Here, I have specified the values for the each builders to visualize their sections on the calender🤗

각 builder의 값들 눈에 띄게끔 적용해보았습니다🤗 (디자인 테러범)

calendarBuilder -> call

CalendarBuilders calendarBuilder() {
    return CalendarBuilders(
      selectedDayBuilder: (context, date, _) {
        return DaisyWidget().buildCalendarDay(
            day: date.day.toString(), backColor: DaisyColors.main4Color);
      },
      todayDayBuilder: (context, date, _) {
        return DaisyWidget().buildCalendarDay(
            day: date.day.toString(), backColor: DaisyColors.backgroundColor);
      },
      dayBuilder: (context, date, _) {
        return DaisyWidget().buildCalendarDay(
            day: date.day.toString(), backColor: Colors.white);
      },
      weekendDayBuilder: (context, date, _) {
        return DaisyWidget().buildCalendarDay(
            day: date.day.toString(),
            backColor: Colors.white,
            color: Colors.red);
      },
      outsideDayBuilder: (context, date, _) {
        return DaisyWidget().buildCalendarDay(
            day: date.day.toString(),
            backColor: Colors.blue,
            color: Colors.red);
      },
      outsideHolidayDayBuilder: (context, date, _) {
        return DaisyWidget().buildCalendarDay(
            day: date.day.toString(),
            backColor: Colors.deepOrange,
            color: Colors.red);
      },
      holidayDayBuilder: (context, date, _) {
        return DaisyWidget().buildCalendarDay(
            day: date.day.toString(),
            backColor: Colors.purple,
            color: Colors.red);
      },
      outsideWeekendDayBuilder: (context, date, _) {
        return DaisyWidget().buildCalendarDay(
            day: date.day.toString(),
            backColor: Colors.pinkAccent,
            color: Colors.black);
      },
      dowWeekdayBuilder: (context, date) {
        return DaisyWidget().buildCalendarDay(
            day: date.toString(), backColor: Colors.yellow, color: Colors.red);
      },
      dowWeekendBuilder: (context, date) {
        return DaisyWidget().buildCalendarDay(
            day: date.toString(), backColor: Colors.green, color: Colors.red);
      },
      unavailableDayBuilder: (context, date, _) {
        return DaisyWidget().buildCalendarDay(
            day: date.day.toString(),
            backColor: Colors.red,
            color: DaisyColors.serveColor);
      },
      markersBuilder: (context, date, events, holidays) {
        final children = <Widget>[];
        if (events.isNotEmpty) {
          children.add(
            Positioned(
              bottom: 1,
              child: _buildEventsMarkerNum(date),
            ),
          );
        }
        return children;
      },
    );
  }

MarkerBuilder -> call

Widget _buildEventsMarkerNum(List events) {
      return DaisyWidget().buildCalendarDayMarker(
          text: '${events.length}',
          backColor: privateLength == 0
              ? DaisyColors.main0Color
              : DaisyColors.serveColor);
    }

buildCalendarDay() , Marker()

Container buildCalendarDay({
    @required String day,
    @required Color backColor,
    Color color,
  }) {
    return Container(
      color: backColor,
      width: 53,
      height: 53,
      child: Center(
        child: Text(day,
            style: TextStyle(fontSize: 12, color: color ?? Colors.black)),
      ),
    );
  }

  AnimatedContainer buildCalendarDayMarker({
    @required String text,
    @required Color backColor,
  }) {
    return AnimatedContainer(
      duration: Duration(milliseconds: 300),
      decoration: BoxDecoration(
        shape: BoxShape.rectangle,
        color: backColor,
      ),
      width: 52,
      height: 13,
      child: Center(
        child: Text(
          text,
          style: TextStyle().copyWith(
            color: Colors.white,
            fontSize: 10.0,
          ),
        ),
      ),
    );
  }

Result

result calendar builder code

CalendarBuilders calendarBuilder() {
    return CalendarBuilders(
      selectedDayBuilder: (context, date, _) {
        return DaisyWidget().buildCalendarDay(
            day: date.day.toString(), backColor: DaisyColors.main4Color);
      },
      todayDayBuilder: (context, date, _) {
        return DaisyWidget().buildCalendarDay(
            day: date.day.toString(), backColor: DaisyColors.backgroundColor);
      },
      dayBuilder: (context, date, _) {
        return DaisyWidget().buildCalendarDay(
            day: date.day.toString(), backColor: Colors.white);
      },
      weekendDayBuilder: (context, date, _) {
        return DaisyWidget().buildCalendarDay(
            day: date.day.toString(),
            backColor: Colors.white,
            color: Colors.red);
      },
      outsideDayBuilder: (context, date, _) {
        return DaisyWidget().buildCalendarDay(
            day: date.day.toString(),
            backColor: Colors.white,
            color: Colors.black26);
      },
      outsideWeekendDayBuilder: (context, date, _) {
        return DaisyWidget().buildCalendarDay(
            day: date.day.toString(),
            backColor: Colors.white,
            color: Colors.red[100]);
      },
      dowWeekdayBuilder: (context, date) {
        return DaisyWidget().buildCalendarDay(
            day: date.toString(),
            backColor: Colors.white,
            color: Colors.black87);
      },
      dowWeekendBuilder: (context, date) {
        return DaisyWidget().buildCalendarDay(
            day: date.toString(),
            backColor: Colors.white,
            color: Colors.red[400]);
      },
      markersBuilder: (context, date, events, holidays) {
        final children = <Widget>[];
        if (events.isNotEmpty) {
          children.add(
            Positioned(
              bottom: 1,
              child: _buildEventsMarkerNum(date, events),
            ),
          );
        }
        return children;
      },
    );
  }