获取 --> 未处理的异常："未来<ThemeModel>"类型不是"主题模型"类型的子类型。 -->错误

Question

当尝试在DropDownButton中选择不同的值时，我得到此错误。但是无法找到错误。

使用Provider包和RXDart的Streams的依赖注入特性，设置BLoC模式更加容易。当状态丢失时，共享首选项可以在分组中存储和恢复数据。

在这个视频中，我们将通过BLoC创建一个动态主题来演示这三个包的有用性，该主题可以在启动时无缝地保存到设备中并从设备中恢复。

我遵循了这个例子https://www.youtube.com/watch?v=ZpLQIFUqaGI

主类

void main() => runApp(Start ());
class Start extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
SystemChrome.setPreferredOrientations([
DeviceOrientation.portraitUp,
]);
final String appTitle = "Opn same";
pageTitle(appTitle);
return ChangeNotifierProvider(
create: (BuildContext context) => PreferenceProvider(),
child: Consumer<PreferenceProvider>(
builder: (context, provider, child) {
return StreamBuilder<ThemeModel>(
stream: provider.bloc.customTheme,
builder: (context, snapshotCustomTheme) {
if (!snapshotCustomTheme.hasData) return Container();
return MaterialApp(
theme: snapshotCustomTheme.data!.customTheme,
title: appTitle,
initialRoute: "/Setting",
routes: routes,
);
});
},
),
);
}
}

设置类:

class Setting extends StatefulWidget {
final String title;
Settings(this.title);
@override
_SettingsState createState() => _SettingsState();
}
class _SettingsState extends State<Settings> {
@override
Widget build(BuildContext context) {
final bloc = Provider.of<Preference>(context).bloc;
return Scaffold(
appBar: AppBar(
title: Text("Settings"),
leading: GestureDetector(
child: Icon(CupertinoIcons.back),
onTap: () {
bloc.savePreferences();
Navigator.of(context).pop();
},
)),
body: Center(
child: ListView(
children: <Widget>[
Padding(
padding: const EdgeInsets.symmetric(horizontal: 15.0),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Text("Theme"),
StreamBuilder<ThemeModel>(
stream:  bloc.customTheme,
builder: (context, snapshot) {
if (!snapshot.hasData) return Container();
return Container(
padding: EdgeInsets.all(20),
child: DropdownButton(
value: snapshot.data!.value,
items: [
DropdownMenuItem(
child: Text("Default"),
value: 1,
),
DropdownMenuItem(
child: Text("Drala"),
value: 2,
),
DropdownMenuItem(
child: Text("gold"),
value: 3,
)
],
onChanged: (int? value)  {
print("value = $value");
setState(() {
bloc.changeTheme(bloc.inToTheme(value!)); **// Getting error here**
});
},
),
);
})
],
),
),
],
),
),
);
}
}

ThemeModel类

class ThemeModel{
final ThemeData customTheme;
final int value;
ThemeModel  ({ required this.customTheme, required this.value,});
}

首选项集团:

class PreferenceBloc {
final _customTheme = BehaviorSubject<ThemeModel>();
//Getters
Stream<Theodel> get customTheme =>  _customTheme.stream;
//Setters
Function(ThemeModel) get chanheme => _customTheme.sink.add;
indexToTheme(int value) {
return _customTheme.firstWhere((x) => x.value==value);
}
savePreferences() async {
SharedPreferences prefs = await Shareferences.getInstance();
await prefs.setInt('themeValue', _customTheme.value.value);
}
loadPreferences() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
int? themeValue = prefs.getInt('themeValue');
if (themeValue != null){
changeTheme(indeheme(themeValue));
} else {
changeTheme(ThemeModel(customTheme: ThemeData(
primaryColor: Color.fromRGBO(58, 66, 86, 1.0),
scaffoldBackgroundColor: Color.fromRGBO(247, 247, 247, 1.0),
brightness: Brightness.light,
visualDensity: VisualDensity(vertical: 0.5, horizontal: 0.5),
primaryColorBrightness: Brightness.light,
primaryTextTheme: TextTheme(
headline6: TextStyle(
fontWeight: FontWeight.w600,
fontFamily: "Raleway",
fontStyle: FontStyle.normal,
fontSize: 22.0,
letterSpacing: 1.6,
wordSpacing: 1.6,
color: Colors.white70,
),
),
),value: 2, ));
}
}
dispose() {
_customTheme.close();
}
}

class PreferenceProvider with ChangeNotifier {
late ThemePreferenceBloc _bloc;
ThemePreferenceProvider() {
_bloc = ThemePreferenceBloc();
_bloc.loadPreferences();
}
ThemeBloc get bloc => _bloc;
}

Error I am getting:

Performing hot restart...
Syncing files to device Android SDK built for x86...
Restarted application in 1,900ms.
I/zygote  ( 6068): Do full code cache collection, code=120KB, data=83KB
I/zygote  ( 6068): After code cache collection, code=111KB, data=66KB
I/flutter ( 6068): value = 3
E/flutter ( 6068): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: type 'Future<ThemeModel>' is not a subtype of type 'ThemeModel'
E/flutter ( 6068): #0      _SettingsState.build.<anonymous closure>.<anonymous closure>.<anonymous closure> (package:open_sesame/view/settings/settings.dart:65:55)
E/flutter ( 6068): #1      State.setState (package:flutter/src/widgets/framework.dart:1088:30)
E/flutter ( 6068): #2      _SettingsState.build.<anonymous closure>.<anonymous closure> (package:open_sesame/view/settings/settings.dart:64:31)
E/flutter ( 6068): #3      _DropdownButtonState._handleTap.<anonymous closure> (package:flutter/src/material/dropdown.dart:1266:25)
E/flutter ( 6068): #4      _rootRunUnary (dart:async/zone.dart:1362:47)
E/flutter ( 6068): #5      _CustomZone.runUnary (dart:async/zone.dart:1265:19)
E/flutter ( 6068): <asynchronous suspension>
E/flutter ( 6068):

请帮. .提前感谢……

Answer 1

如果我不得不猜你错过了一个await，你正在调用Future<ThemeModel>类型的函数

如果你想在这里进一步调试它，可以分享一个完整的例子。

Answer 2

我无法让它工作的原因是我无法访问存储在另一个文件中的数据。现在我把数据放到同一个文件中。

import 'package:flutter/material.dart';
import 'package:rxdart/subjects.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:testing/models/color.dart';
class PreferenceBloc{
final _brightness = BehaviorSubject<Brightness>();
final _primaryColor = BehaviorSubject<ColorModel>();
final _colors = [
ColorModel(color: Colors.blue,index: 0.0, name: 'Blue'),
ColorModel(color: Colors.green,index: 1.0, name: 'Green'),
ColorModel(color: Colors.red,index: 2.0, name: 'Red'),
ColorModel(color: Colors.white,index: 3.0, name: 'White'),
];
//Getters
Stream<Brightness> get brightness => _brightness.stream;
Stream<ColorModel> get primaryColor => _primaryColor.stream;
//Setters
Function(Brightness) get changeBrightness => _brightness.sink.add;
Function(ColorModel) get changePrimaryColor => _primaryColor.sink.add;
indexToPrimaryColor(double index){
return _colors.firstWhere((x) => x.index==index);
}
savePreferences() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
if (_brightness.value == Brightness.light){
await prefs.setBool('dark', false);
}  else {
await prefs.setBool('dark', true);
}
await prefs.setDouble('colorIndex', _primaryColor.value.index);
}
loadPreferences() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
bool? darkMode=prefs.getBool('dark');
double? colorIndex = prefs.getDouble('colorIndex');
if (darkMode != null){
(darkMode == false) ? changeBrightness(Brightness.light) : changeBrightness(Brightness.dark);
} else {
changeBrightness(Brightness.light);
}
if (colorIndex != null){
changePrimaryColor(indexToPrimaryColor(colorIndex));
} else {
changePrimaryColor(ColorModel(color: Colors.blue,index: 0.0, name: 'Blue'));
}
}
dispose(){
_primaryColor.close();
_brightness.close();
}
}