Unhandled Exception: LateInitializationError: Field '_deviceCalendarPlugin#332335403' has not been initialized - flutter

Question

I am getting the error:
Unhandled Exception: LateInitializationError: Field '_deviceCalendarPlugin#332335403' has not been initialized.late DeviceCalendarPlugin _deviceCalendarPlugin
This statement getting error I am adding ? sign but in console the error is showing null string is not supporting.
I am creating doctor appointment event
class DoctorCalendarsPage extends StatefulWidget {
const DoctorCalendarsPage({Key? key, required String calendarName, required void Function() opendrawer, required double animationtime})
: super(key: key);
#override
_DoctorCalendarsPageState createState() {
return _DoctorCalendarsPageState();
}
}
class _DoctorCalendarsPageState extends State<DoctorCalendarsPage> {
late DeviceCalendarPlugin _deviceCalendarPlugin;
List<Calendar> _calendar = [];
List<Calendar> get _writableCalendars =>
_calendar.where((c) => c.isReadOnly == false).toList();
List<Calendar> get _readOnlyCalendars =>
_calendar.where((c) => c.isReadOnly == true).toList();
_CalendarsPageState() {
_deviceCalendarPlugin = DeviceCalendarPlugin();
}
#override
void initState() {
super.initState();
_retrieveCalendars();
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: Column(
children: [
Expanded(
flex: 1,
child: ListView.builder(
itemCount: _calendar.length,
itemBuilder: (BuildContext context, int index) {
return GestureDetector(
key: Key(_calendar[index].isReadOnly == true
? 'readOnlyCalendar${_readOnlyCalendars.indexWhere((c) => c.id == _calendar[index].id)}'
: 'writableCalendar${_writableCalendars.indexWhere((c) => c.id == _calendar[index].id)}'),
onTap: () async {
await Navigator.push(context,
MaterialPageRoute(builder: (BuildContext context) {
return DoctorEventsPage(_calendar[index],
key: const Key('calendarEventsPage'));
}));
},
child: Padding(
padding: const EdgeInsets.all(10.0),
child: Container(
height: 22,
child: Row(
children: [
Expanded(
flex: 1,
child: Text(
_calendar[index].name!,
style: Theme.of(context).textTheme.subtitle1,
),
),
Container(
width: 15,
height: 15,
decoration: BoxDecoration(
shape: BoxShape.circle,
color: Color(_calendar[index].color!)),
),
const SizedBox(width: 10),
// Container(
// margin: const EdgeInsets.fromLTRB(0, 0, 5.0, 0),
// padding: const EdgeInsets.all(3.0),
// decoration: BoxDecoration(
// border: Border.all(color: Colors.blueAccent)),
// // child: const Text('Default'),
// ),
Icon(_calendar[index].isReadOnly == true
? Icons.lock
: Icons.lock_open)
],
),
),
),
);
},
),
),
],
),
floatingActionButton: FloatingActionButton(
onPressed: () async {
final createCalendar = await Navigator.push(context,
MaterialPageRoute(builder: (BuildContext context) {
return DoctorCalendarAddPage();
}));
if (createCalendar == true) {
_retrieveCalendars();
}
},
child: const Icon(Icons.add),
backgroundColor: Colors.green,
),
);
}
void _retrieveCalendars() async {
try {
var permissionsGranted = await _deviceCalendarPlugin.hasPermissions();
if (permissionsGranted.isSuccess &&
(permissionsGranted.data == null ||
permissionsGranted.data == false)) {
permissionsGranted = await _deviceCalendarPlugin.requestPermissions();
if (!permissionsGranted.isSuccess ||
permissionsGranted.data == null ||
permissionsGranted.data == false) {
return;
}
}
final calendarsResult = await _deviceCalendarPlugin.retrieveCalendars();
setState(() {
_calendar = calendarsResult.data as List<Calendar>;
});
} on PlatformException catch (e) {
if (kDebugMode) {
print(e);
}
}
}
}

Answer 1

Add _CalendarsPageState in your init state
#override
void initState() {
super.initState();
_retrieveCalendars();
_CalendarsPageState();
}

Answer 2

The following mean the variable will never be null.. so u have to assign it first before using it
late DeviceCalendarPlugin _deviceCalendarPlugin;
-----------------------------
You can use the following way.. so until u have get the data u want to assign the variable will be null
DeviceCalendarPlugin? _deviceCalendarPlugin;

Answer 3

Try initializing the instance first before calling it's function. Add _deviceCalendarPlugin = DeviceCalendarPlugin(); or _CalendarsPageState() prior to calling anything related to its function.