Passing List<Events> back to eventLoader property from function in flutter app gives error

Question

I am trying to populate events on a table_calendar widget in my Flutter app but I am having trouble working with the events and the eventsLoader: property of the table_calendar widget.

I have figured out that if I use 2 for loops I can populate a list of type Events, List, and pass it back to eventsLoader but I am getting an error I don't understand.

Here is the code I am using:

      eventLoader: (day) {
        return _getEventsForDay(day, events);  <<< ERROR HERE
      },

  List<Events>? _getEventsForDay(DateTime day, [List<Events>? events]) {
    final int today = day.day;
    final int nbrEvents = events!.length;

    for (Events allEvent in events) {
      if (day.year == allEvent.eventDate!.year &&
          day.month == allEvent.eventDate!.month &&
          day.day == allEvent.eventDate!.day) {
        // fill this list with all the events associated
        //with the given day and pass the list back
        late final List<Events> listDayEvents = [];
        for (Events dayEvents in events) {
          if (day.year == allEvent.eventDate!.year &&
              day.month == allEvent.eventDate!.month &&
              day.day == allEvent.eventDate!.day) {
            listDayEvents.add(allEvent);
          }
        }
        return listDayEvents;
      }
      List<Events> emptyList = [];
      return emptyList;
    }
  }

The error I am getting on the eventsLoader: property is this:

The return type 'List<Events>?' isn't a 'List<_>', as required by the closure's context.dartreturn_of_invalid_type_from_closure
List<Events>? _getEventsForDay(DateTime day, [List<Events>? events])
Type: List<Events>? Function(DateTime, [List<Events>?])

package:deal_diligence/screens/appointment_calendar.dart

I don't understand this error message since I am returning a List type.

Here is the Events class. I am getting the events from a Firebase collection and each event has the data element in the Events class so am I passing the wrong type of data?

class Events {
  String? id;
  String? eventName;
  DateTime? eventStartTime;
  String? eventDuration;
  DateTime? eventDate;
  String? eventDescription;
  String? userId;
  String? companyId;

Here is the link to the documentation for table_calendar widget

What am I doing wrong? Please help. Thanks

Answer 1

1.The issue might be due to the return types and the way you're handling the function _getEventsForDay.

2.The error specifically points to the closure's context, stating that the return type isn't of the correct type _, which is expected by the closure.

Let's address the issues:

Null Safety: It's important to handle null safety properly, especially when dealing with Firebase data that might contain nullable values.

Function Return Type: Ensure that the function _getEventsForDay returns the correct type according to the expected signature of the eventsLoader.

Try to update like this,

List<Events> _getEventsForDay(DateTime day, List<Events>? events) {
  List<Events> listDayEvents = [];

  if (events == null) {
    return listDayEvents; // Return an empty list if events is null
  }

  for (Events event in events) {
    if (event.eventDate != null &&
        day.year == event.eventDate!.year &&
        day.month == event.eventDate!.month &&
        day.day == event.eventDate!.day) {
      listDayEvents.add(event);
    }
  }

  return listDayEvents;
}

3.Ensure that you're providing a list of Events to this function, and it will return a list of events corresponding to the given day. Make sure to handle null events appropriately.

In your eventLoader property, use the modified function like this,

eventLoader: (day) {
  return _getEventsForDay(day, events ?? []); // Pass an empty list if events is null
},

4.This ensures that you're passing a list to _getEventsForDay and handling cases where the events might be null. Also, make sure to handle null values in the eventDate property within the Events class, as I assumed it might be nullable based on your class definition.