未来完成后，Flutter FutureProvider不会更新子级

Question

我正在使用提供程序包。我正在使用FutureProvider加载json文件。 FutureProvider还具有一个ChangeNotifierProvider作为子级。我不确定这样做时会出什么问题，但是我的孩子没有得到重建。

使用提供程序的底页：

class AddClockBottomSheet extends StatelessWidget {
  final LoadTimeZoneRegionProvider _loadTimeZoneRegionProvider = LoadTimeZoneRegionProvider();

  @override
  Widget build(BuildContext context) {
    return FutureProvider<List<TimeZoneRegion>>.value (
        initialData: _loadTimeZoneRegionProvider.timeZoneRegionList,
        value: _loadTimeZoneRegionProvider.loadTimeZoneRegionList(),
        child: Consumer<List<TimeZoneRegion>>(
          builder: (context, timeZoneRegionList, child) {
            return ChangeNotifierProvider<AddClockProvider>(
              builder: (_) => AddClockProvider(timeZoneRegionList),
              child: Consumer<AddClockProvider>(
                builder: (context, addClockProvider, child) {
                return Container(
                  padding: EdgeInsets.all(20.0),
                  child: Column(
                    crossAxisAlignment: CrossAxisAlignment.stretch,
                    children: <Widget>[
                      Text(
                        "Add Clock",
                        textAlign: TextAlign.center,
                        style: TextStyle(
                            fontSize: 30.0,
                            color: Theme
                                .of(context)
                                .appBarTheme
                                .color
                        ),
                      ),
                      TextField(
                        decoration: InputDecoration(
                          labelText: "Clock label",
                        ),
                        textAlign: TextAlign.center,
                        autofocus: true,
                      ),
                      DropdownButton<TimeZoneRegion>(
                        value: addClockProvider.timeZoneRegion,
                        icon: Icon(Icons.arrow_downward),
                        iconSize: 24,
                        elevation: 16,
                        underline: Container(
                          height: 2,
                          color: Theme
                              .of(context)
                              .appBarTheme
                              .color,
                        ),
                        onChanged: addClockProvider.updateTimeZoneRegionDropdown,
                        items: addClockProvider.timeZoneRegionDropDownMenuItemList,
                      ),
                      FlatButton(
                        child: Text(
                          "Add",
                          style: TextStyle(
                            color: Theme
                                .of(context)
                                .accentTextTheme
                                .title
                                .color,
                          ),
                        ),
                        color: Theme
                            .of(context)
                            .accentColor,
                        onPressed: () {},
                      ),
                    ],
                  ),
                );
          },
              ),
            );
          }),
    );
  }
}

要从json文件加载数据的提供程序。

class LoadTimeZoneRegionProvider {

  List<TimeZoneRegion> timeZoneRegionList = List();



  Future<List<TimeZoneRegion>> loadTimeZoneRegionList() async {
    TimeZoneFileHandler handler = TimeZoneFileHandler();
    timeZoneRegionList = await handler.parseTimeZones();
    print(timeZoneRegionList);
    return timeZoneRegionList;
  }
}

将与DropDownButton交互的提供程序。

class AddClockProvider with ChangeNotifier {
  final List<TimeZoneRegion> timeZoneRegionList;

  TimeZoneRegion timeZoneRegion;
  TimeZone timeZone;

  AddClockProvider(this.timeZoneRegionList);

  UnmodifiableListView<
      DropdownMenuItem<TimeZoneRegion>> _mapTimeZoneRegionList() {
    return UnmodifiableListView<
        DropdownMenuItem<TimeZoneRegion>>(
        timeZoneRegionList.map<DropdownMenuItem<TimeZoneRegion>>((
            TimeZoneRegion timeZoneRegion) {
          return DropdownMenuItem<TimeZoneRegion>(
            value: timeZoneRegion,
            child: Text(timeZoneRegion.name),
          );
        }
        ).toList());
  }

  UnmodifiableListView<
      DropdownMenuItem<TimeZoneRegion>> get timeZoneRegionDropDownMenuItemList {
    return _mapTimeZoneRegionList();
  }

  List<DropdownMenuItem<TimeZone>> get timeZoneList {
    return timeZoneRegion.timeZones
        .map<DropdownMenuItem<TimeZone>>((TimeZone timeZone) {
      return DropdownMenuItem<TimeZone>(
        value: timeZone,
        child: Text("${DurationParser.formatDuration(timeZone.offset)} ${timeZone.name}"),
      );
    }
    ).toList();
  }

  void updateTimeZoneRegionDropdown(TimeZoneRegion newTimeZoneRegion) {
    timeZoneRegion = newTimeZoneRegion;
    notifyListeners();
  }

  void updateTimeZoneDropdown(TimeZone newTimeZone) {
    timeZone = newTimeZone;
    notifyListeners();
  }
}