我的项目中有一个日历，我有一个按钮可以将事件添加到该日历中的日期。当我尝试按下添加按钮来添加一个事件时，我得到了方法 '[]' 在 null 上被调用。接收者：null 尝试调用：[]('DateTime' 的实例)。有些东西返回 null，但我不明白是什么。你能帮我吗？
这是我的代码：
calendar.dart
import 'package:flutter_calendar_carousel/classes/event.dart';
import 'package:flutter_calendar_carousel/flutter_calendar_carousel.dart';
import 'package:intl/intl.dart';
class Home extends StatefulWidget {
@override
_HomeState createState() => _HomeState();
}
class _HomeState extends State<Home> {
DateTime _currentDate = DateTime.now();
DateTime _currentDate2 = DateTime.now();
String _currentMonth = DateFormat.yMMM().format(DateTime.now());
DateTime _targetDateTime = DateTime.now();
Map<DateTime, List<Event>> selectedEvents;
DateTime selectedDay = DateTime.now();
DateTime focusedDay = DateTime.now();
TextEditingController _eventController = TextEditingController();
CalendarCarousel _calendarCarouselNoHeader;
static Widget _eventIcon = new Container(
decoration: new BoxDecoration(
color: Colors.white,
borderRadius: BorderRadius.all(Radius.circular(1000)),
border: Border.all(color: Colors.blue, width: 2.0)),
child: new Icon(
Icons.person,
color: Colors.amber,
),
);
EventList<Event> _markedDateMap = new EventList<Event>(
events: {
new DateTime(2020, 2, 10): [
new Event(
date: new DateTime(2020, 2, 14),
title: 'Event 1',
icon: _eventIcon,
dot: Container(
margin: EdgeInsets.symmetric(horizontal: 1.0),
color: Colors.red,
height: 5.0,
width: 5.0,
),
),
new Event(
date: new DateTime(2020, 2, 10),
title: 'Event 2',
icon: _eventIcon,
),
new Event(
date: new DateTime(2020, 2, 15),
title: 'Event 3',
icon: _eventIcon,
),
],
},
);
@override
void initState() {
_markedDateMap.add(
new DateTime(2020, 2, 25),
new Event(
date: new DateTime(2020, 2, 25),
title: 'Event 5',
icon: _eventIcon,
));
_markedDateMap.add(
new DateTime(2020, 2, 10),
new Event(
date: new DateTime(2020, 2, 10),
title: 'Event 4',
icon: _eventIcon,
));
_markedDateMap.addAll(new DateTime(2019, 2, 11), [
new Event(
date: new DateTime(2019, 2, 11),
title: 'Event 1',
icon: _eventIcon,
),
new Event(
date: new DateTime(2019, 2, 11),
title: 'Event 2',
icon: _eventIcon,
),
new Event(
date: new DateTime(2019, 2, 11),
title: 'Event 3',
icon: _eventIcon,
),
]);
super.initState();
}
@override
Widget build(BuildContext context) {
_calendarCarouselNoHeader = CalendarCarousel<Event>(
todayBorderColor: Color(0xFF3EB16F),
onDayPressed: (DateTime date, List<Event> events) {
this.setState(() => _currentDate2 = date);
events.forEach((event) => print(event.title));
},
daysHaveCircularBorder: true,
showOnlyCurrentMonthDate: false,
weekendTextStyle: TextStyle(
color: Colors.red,
),
thisMonthDayBorderColor: Colors.grey,
weekFormat: false,
// firstDayOfWeek: 4,
markedDatesMap: _markedDateMap,
height: 420.0,
selectedDateTime: _currentDate2,
targetDateTime: _targetDateTime,
customGridViewPhysics: NeverScrollableScrollPhysics(),
markedDateCustomShapeBorder:
CircleBorder(side: BorderSide(color: Colors.yellow)),
markedDateCustomTextStyle: TextStyle(
fontSize: 18,
color: Colors.blue,
),
showHeader: false,
todayTextStyle: TextStyle(
color: Colors.blue,
),
todayButtonColor: Colors.yellow,
selectedDayTextStyle: TextStyle(
color: Colors.yellow,
),
minSelectedDate: _currentDate.subtract(Duration(days: 360)),
maxSelectedDate: _currentDate.add(Duration(days: 360)),
prevDaysTextStyle: TextStyle(
fontSize: 16,
color: Colors.pinkAccent,
),
inactiveDaysTextStyle: TextStyle(
color: Colors.tealAccent,
fontSize: 16,
),
onCalendarChanged: (DateTime date) {
this.setState(() {
_targetDateTime = date;
_currentMonth = DateFormat.yMMM().format(_targetDateTime);
});
},
onDayLongPressed: (DateTime date) {
print('long pressed date $date');
},
);
return new Scaffold(
appBar: AppBar(
toolbarHeight: 90,
backgroundColor: Color(0xFF3EB16F),
title: Text("Calendar"),
centerTitle: true,
textTheme: TextTheme(
headline6: TextStyle(fontSize: 44, fontFamily: "Angel"),
),
),
body: SingleChildScrollView(
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
//custom icon
Container(
margin: EdgeInsets.only(
top: 30.0,
bottom: 16.0,
left: 16.0,
right: 16.0,
),
child: new Row(
children: <Widget>[
Expanded(
child: Text(
_currentMonth,
style: TextStyle(
fontWeight: FontWeight.bold,
fontSize: 24.0,
),
)),
FlatButton(
child: Text('PREV'),
onPressed: () {
setState(() {
_targetDateTime = DateTime(
_targetDateTime.year, _targetDateTime.month - 1);
_currentMonth =
DateFormat.yMMM().format(_targetDateTime);
});
},
),
FlatButton(
child: Text('NEXT'),
onPressed: () {
setState(() {
_targetDateTime = DateTime(
_targetDateTime.year, _targetDateTime.month + 1);
_currentMonth =
DateFormat.yMMM().format(_targetDateTime);
});
},
)
],
),
),
Container(
margin: EdgeInsets.symmetric(horizontal: 16.0),
child: _calendarCarouselNoHeader,
), //
],
),
),
floatingActionButton: FloatingActionButton.extended(
onPressed: () => showDialog(
context: context,
builder: (context) => AlertDialog(
title: Text("Add Event"),
content: TextFormField(
controller: _eventController,
),
actions: [
TextButton(
onPressed: () => Navigator.pop(context),
child: Text("Cancel"),
),
TextButton(
child: Text("Add"),
onPressed: () {
if (_eventController.text.isEmpty) {
} else {
if (selectedEvents[selectedDay] != null) {
selectedEvents[selectedDay].add(
Event(title: _eventController.text),
);
} else {
selectedEvents[selectedDay] = [
Event(title: _eventController.text)
];
}
}
Navigator.pop(context);
_eventController.clear();
setState(() {});
return;
},
),
],
),
),
label: Text("Add"),
icon: Icon(Icons.add),
));
}
}
event.dart
class Event {
final String title;
Event({@required this.title});
String toString() => this.title;
}
答案 0 :(得分：0)
selectedEvents 变量为空，因此在尝试通过键访问该值时会出现此错误。您需要做的是避免使用空映射启动此变量：
Map<DateTime, List<Event>> selectedEvents = <DateTime, List<Event>>{};
此外，您可以使用 Map 方法来代替检查值是否为空，例如：
而不是这样调用：
if (selectedEvents[selectedDay] != null) {...}
使用专用方法：
if (selectedEvents.containsKey(selectedDay)) {...}