在ScrollablePositionedList（这是日历）的第一版中出现此错误。
最初，我声明一个空的List<DateTime> calendar = [];，其中填充了带有状态的日期（我正在使用flutter_bloc），并调用一个方法来检查今天的日期是否在列表中并滚动到该索引，否则滚动到索引0（每月的第一天）。
除了Bloc的InitialState为空之外，我有两种不同的状态，一种是TodayDate用于在屏幕加载时在当月构建窗口小部件，另一种是NewDate，用于在日历中更改月份时重新构建窗口小部件。
我仅在收到TodayDate状态时才收到错误消息（请参阅打印1），但是当更改月份时，一切都会按预期进行（请参见打印2和3）。
我无法确定为什么在第一个小部件构建中会抛出错误，因为可用数据与打印3相同。
最初，我认为这可能与InitialState为空有关，但随后TodayDate状态随数据一起出现，应该可以修复错误。此外，打印显示国家交易后的错误。
您能在我的实现中看到任何错误吗？ 一如既往，非常感谢您的时间和帮助。
Expanded(
// child: ListView.builder(
// controller: scrollController,
child: ScrollablePositionedList.builder(
itemScrollController: scrollController,
itemCount: calendar.length,
itemBuilder: (BuildContext context, int index) =>
CalendarCell(
day: calendarFormat
.format(calendar[index]),
borderColor: isSelectedDay[index] == true
? Colors.white
: dateCheckIsToday.format(
calendar[index]) ==
dateCheckIsToday
.format(DateTime.now())
? Colors.greenAccent
: getDayNameShort.format(
calendar[index]) ==
'Sun'
? Colors.redAccent
: Colors.orangeAccent,
isSelected: isSelectedDay[index],
onTap: () {
BlocProvider.of<CalendarBloc>(context)
.add(UpdateCalendarSelectedDay(
isSelectedDay, index));
BlocProvider.of<CalendarBloc>(context)
.add(GetOpeningTimeSlots(
weekday:
'${getDayNameShort.format(calendar[index])}',
date: calendar[index]));
},
),
flex: 2,
),
if (state is TodayDate) {
setState(() {
displayDate = state.newDate;
print(displayDate);
calendar = state.calendar;
isSelectedDay = state.isSelectedDay;
scrollToIndex(
calendar);
// RangeError (index): Invalid value: Not in range 0..30, inclusive: -1
});
}
if (state is NewDate) {
setState(() {
displayDate = state.newDate;
calendar = state.calendar;
isSelectedDay = state.isSelectedDay;
scrollToIndex(calendar); // works perfectly
// print('calendar is ${state.calendar}');
// print('isDaySelectedDay is ${state.isSelectedDay}');
});
}
void scrollToIndex(List<DateTime> calendar) {
print('scrollToIndex called');
indexToScrollTo = 0;
for (int index = 0; index < calendar.length; index++) {
dateCheckIsToday.format(DateTime.now());
if (dateCheckIsToday.format(calendar[index]) ==
dateCheckIsToday.format(DateTime.now())) {
indexToScrollTo = index;
break;
}
}
print('indexToScrolTo is: $indexToScrollTo');
scrollController.jumpTo(
index: indexToScrollTo); //, duration: Duration(seconds: 1));
}
TodayDate状态为5月份的实际打印：flutter: Event is GetMonth : {actual date :2020-05-17 08:08:41.044548}
flutter: Transaction is Transition { currentState: InitialState : { date: 2000-01-01 00:00:00.000, calendar : [], isSelected :[]}, event: GetMonth : {actual date :2020-05-17 08:08:41.044548}, nextState: TodayDate : { date: 2020-05-17 08:08:41.044548, calendar : [2020-05-01 00:00:00.000, 2020-05-02 00:00:00.000, 2020-05-03 00:00:00.000, 2020-05-04 00:00:00.000, 2020-05-05 00:00:00.000, 2020-05-06 00:00:00.000, 2020-05-07 00:00:00.000, 2020-05-08 00:00:00.000, 2020-05-09 00:00:00.000, 2020-05-10 00:00:00.000, 2020-05-11 00:00:00.000, 2020-05-12 00:00:00.000, 2020-05-13 00:00:00.000, 2020-05-14 00:00:00.000, 2020-05-15 00:00:00.000, 2020-05-16 00:00:00.000, 2020-05-17 00:00:00.000, 2020-05-18 00:00:00.000, 2020-05-19 00:00:00.000, 2020-05-20 00:00:00.000, 2020-05-21 00:00:00.000, 2020-05-22 00:00:00.000, 2020-05-23 00:00:00.000, 2020-05-24 00:00:00.000, 2020-05-25 00:00:00.000, 2020-05-26 00:00:00.000, 2020-05-27 00:00:00.000, 2020-05-28 00:00:00.000, 2020-05-29 00:00:00.000, 2020-05-30 00:00:00.0<…>
flutter: 2020-05-17 08:08:41.044548
flutter: scrollToIndex called
flutter: indexToScrolTo is: 16
════════ (4) Exception caught by widgets library ═══════════════════════════════════════════════════
RangeError (index): Invalid value: Not in range 0..30, inclusive: -1
════════════════════════════════════════════════════════════════════════════════════════════════════
NewDate将月份更改为六月时的状态：flutter: Event is NextMonth : {actual date :2020-05-17 08:08:41.044548}
flutter: Transaction is Transition { currentState: TodayDate : { date: 2020-05-17 08:08:41.044548, calendar : [2020-05-01 00:00:00.000, 2020-05-02 00:00:00.000, 2020-05-03 00:00:00.000, 2020-05-04 00:00:00.000, 2020-05-05 00:00:00.000, 2020-05-06 00:00:00.000, 2020-05-07 00:00:00.000, 2020-05-08 00:00:00.000, 2020-05-09 00:00:00.000, 2020-05-10 00:00:00.000, 2020-05-11 00:00:00.000, 2020-05-12 00:00:00.000, 2020-05-13 00:00:00.000, 2020-05-14 00:00:00.000, 2020-05-15 00:00:00.000, 2020-05-16 00:00:00.000, 2020-05-17 00:00:00.000, 2020-05-18 00:00:00.000, 2020-05-19 00:00:00.000, 2020-05-20 00:00:00.000, 2020-05-21 00:00:00.000, 2020-05-22 00:00:00.000, 2020-05-23 00:00:00.000, 2020-05-24 00:00:00.000, 2020-05-25 00:00:00.000, 2020-05-26 00:00:00.000, 2020-05-27 00:00:00.000, 2020-05-28 00:00:00.000, 2020-05-29 00:00:00.000, 2020-05-30 00:00:00.000, 2020-05-31 00:00:00.000], isSelected :[false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, fals<…>
flutter: scrollToIndex called
flutter: indexToScrolTo is: 0
NewDate用于将月份更改为5月份的打印：flutter: Event is PreviousMonth :{actual date :2020-06-17 00:00:00.000}
flutter: Transaction is Transition { currentState: NewDate : { date: 2020-06-17 00:00:00.000, calendar : [2020-06-01 00:00:00.000, 2020-06-02 00:00:00.000, 2020-06-03 00:00:00.000, 2020-06-04 00:00:00.000, 2020-06-05 00:00:00.000, 2020-06-06 00:00:00.000, 2020-06-07 00:00:00.000, 2020-06-08 00:00:00.000, 2020-06-09 00:00:00.000, 2020-06-10 00:00:00.000, 2020-06-11 00:00:00.000, 2020-06-12 00:00:00.000, 2020-06-13 00:00:00.000, 2020-06-14 00:00:00.000, 2020-06-15 00:00:00.000, 2020-06-16 00:00:00.000, 2020-06-17 00:00:00.000, 2020-06-18 00:00:00.000, 2020-06-19 00:00:00.000, 2020-06-20 00:00:00.000, 2020-06-21 00:00:00.000, 2020-06-22 00:00:00.000, 2020-06-23 00:00:00.000, 2020-06-24 00:00:00.000, 2020-06-25 00:00:00.000, 2020-06-26 00:00:00.000, 2020-06-27 00:00:00.000, 2020-06-28 00:00:00.000, 2020-06-29 00:00:00.000, 2020-06-30 00:00:00.000],isSelected :[false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, <…>
flutter: scrollToIndex called
flutter: indexToScrolTo is: 16
如打印所显示的，当更改月份并收到NewDate状态时，小部件正确更新，并且更改回实际月份时，它的行为也符合预期，跳到今天的日期。那么，为什么TodayDate失败了，却承载了相同的数据，并且对滚动方法的调用与NewDate相同？
使用Timer延迟对scrollToIndex方法的调用使其正常工作。希望这有助于了解问题出在哪里。
if (state is TodayDate) {
setState(() {
displayDate = state.newDate;
print(displayDate);
calendar = state.calendar;
isSelectedDay = state.isSelectedDay;
Timer(Duration(milliseconds: 50), () {
scrollToIndex(calendar);
});
// timer makes it work
// RangeError (index): Invalid value: Not in range 0..30, inclusive: -1
});
// scrollToIndex(calendar);
}