add event to TableCalender flutter-CodePudding

I am new in create calender in flutter. I try to create table_calendar, and add event to the calender but I got an error.

The code I did:

Map<DateTime, List> _events = {};
DateTime _focusedDay = DateTime.now();
DateTime _selectedDate;
@override
void initState() {
_selectedDate = _focusedDay;
DateTime d = DateTime.utc(DateTime.now().year, DateTime.now().month, DateTime.now().day, 12);
_events[d] = [];
_events[d].add("Event A");
super.initState();
}

@override
Widget build(BuildContext context) {
return Column(
children: [
 TableCalendar(
  focusedDay: _focusedDay,
    onDaySelected: (selectedDay, focusedDay) {
      if (!isSameDay(_selectedDate, selectedDay)) {
        setState(() {
          _selectedDate = selectedDay;
          _focusedDay = focusedDay;
        });
      }
    },
    eventLoader: (day) {
      return _events.keys.contains(day) ? _events[day] : [];
    },
  )
],
);

The error I got is: The following NoSuchMethodError was thrown building Calender(dirty, state: _CalenderState#3429f): The getter 'year' was called on null. Receiver: null Tried calling: year

CodePudding user response：

It looks like your main problem is this line in your initState():

DateTime d = DateTime.utc(DateTime.now().year, DateTime.now().month, DateTime.now().day, 12);

The eventLoader is passed DateTimes at midnight (at 00:00:00.000). When you add "Event A" to your event map, the key you give it is a DateTime for today at noon since you give it an hour parameter of 12. In the event loader, you check if there's a value in your event map with a key of today at midnight. Since there isn't, it thinks there's no event today.

You're also missing the firstDay and lastDay parameter for your TableCalendar, which are both required.

It seems like the error you mentioned is coming from code outside of the snippet you posted. Your only use of the 'year' getter is DateTime.now().year, which is perfectly valid.

Below is an example of the calendar widget with those two fixes applied. I also added several other small improvements to your code with comments explaining those improvements. Here's a link to an image showing the resulting calendar, which properly shows the event you added to today's date:

The resulting calendar running in an iOS simulator

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

  @override
  State<Calendar> createState() => _CalendarState();
}

class _CalendarState extends State<Calendar> {
  final Map<DateTime, List> _events = {};

  DateTime _focusedDay = DateTime.now();

  // Instead of initializing in initState, just add the "late" modifier.
  late DateTime _selectedDate = _focusedDay;

  @override
  void initState() {
    // This is where your problem is. The event loader is passed DateTimes with
    // the time component set to zero (midnight). d is set to noon. Just delete
    // the argument of "12" for hours.
    DateTime d = DateTime.utc(
      DateTime.now().year,
      DateTime.now().month,
      DateTime.now().day,
    );
    // Just add "Event A" to the list on this line
    _events[d] = ["Event A"];
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        TableCalendar(
          // Make sure you add the required arguments "firstDay" and "lastDay"
          firstDay: DateTime(1970),
          lastDay: DateTime.now(),
          focusedDay: _focusedDay,
          onDaySelected: (selectedDay, focusedDay) {
            if (!isSameDay(_selectedDate, selectedDay)) {
              setState(() {
                _selectedDate = selectedDay;
                _focusedDay = focusedDay;
              });
            }
          },
          eventLoader: (day) {
            // Use a null aware operator "??" to make this line simpler. If
            // _events[day] is null, return the empty list instead.
            return _events[day] ?? [];
          },
        )
      ],
    );
  }
}