未处理的异常:没有找到MaterialLocalizations

Question

我试图显示警告对话框，以便使用firebase配置强制更新我的应用程序版本，从versionCheck(context) ()调用showVersionDialog()一切都很好，但是当我调用showVersionDialog()方法时会出错，下面是我的代码

void main() => runApp(UniApp());

class UniApp extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => _UniappMainState();
}
class _UniappMainState extends State<UniApp> {
  AppTranslationsDelegate _newLocaleDelegate;

  @override
  void initState() {
    super.initState();
    setlocaleFromSharedPreference();
    _newLocaleDelegate = AppTranslationsDelegate(newLocale: null);
    UAAppContext.getInstance().onLocaleChanged = onLocaleChange;
//calling versionCheck
    versionCheck(context);
  }

  versionCheck(context) async {
    //Get Current installed version of app
    final PackageInfo info = await PackageInfo.fromPlatform();
    double currentVersion = double.parse(info.version.trim().replaceAll(".", ""));

    //Get Latest version info from firebase config
    final RemoteConfig remoteConfig = await RemoteConfig.instance;

    try {
      // Using default duration to force fetching from remote server.
      await remoteConfig.fetch(expiration: const Duration(seconds: 0));
      remoteConfig.setConfigSettings(RemoteConfigSettings(debugMode: true));
      await remoteConfig.activateFetched();
      remoteConfig.getString('force_update_current_version');
      double newVersion = double.parse(remoteConfig
          .getString('force_update_current_version')
          .trim()
          .replaceAll(".", ""));
      print("cv-"+currentVersion.toString()+"nv--"+newVersion.toString());
      if (newVersion > currentVersion) {
        _showVersionDialog(context);
      }
    } on FetchThrottledException catch (exception) {
      // Fetch throttled.
      print(exception);
    } catch (exception) {
      print('Unable to fetch remote config. Cached or default values will be '
          'used');
    }
  }

  //Show Dialog to force user to update
  _showVersionDialog(context) async {
    await showDialog<String>(
      context: context,
      barrierDismissible: false,
      builder: (BuildContext context) {
        String title = "New Update Available";
        String message =
            "There is a newer version of app available please update it now.";
        String btnLabel = "Update Now";
        String btnLabelCancel = "Later";
        return new AlertDialog(
          title: Text(title),
          content: Text(message),
          actions: <Widget>[
            FlatButton(
              child: Text(btnLabel),
              onPressed: () => _launchURL(CommonConstants.PLAY_STORE_URL),
            ),
            FlatButton(
              child: Text(btnLabelCancel),
              onPressed: () => Navigator.pop(context),
            ),
          ],
        );
      },
    );
  }
  _launchURL(String url) async {
    if (await canLaunch(url)) {
      await launch(url);
    } else {
      throw 'Could not launch $url';
    }
  }


  void onLocaleChange(Locale locale) {
    setState(() {
      UAAppContext.getInstance().changeLanguage(locale.languageCode);
      _newLocaleDelegate = AppTranslationsDelegate(newLocale: locale);
    });
  }

  setlocaleFromSharedPreference() {
    UAAppContext.getInstance().getLocale().then((locale) {
      if (locale == 'en') return;
      setState(() {
        _newLocaleDelegate = AppTranslationsDelegate(newLocale: Locale(locale));
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      initialRoute: '/',
      routes: {
        '/': (context) => SplashScreen(),
        CommonConstants.homeRoute: (context) { RouteParameters r = ModalRoute.of(context).settings.arguments;
        if (r != null && r.appId != null && r.appId.isNotEmpty) {
          return HomeScreen(
            parentAppId: r.appId
          );
        } else return HomeScreen();},
        CommonConstants.loginRoute: (context) => LoginScreen(),
        CommonConstants.projectGroupRoute: (context) {
          RouteParameters r = ModalRoute.of(context).settings.arguments;
          if (r != null && r.appId != null && r.appId.isNotEmpty) {
            return ProjectGroupScreen(
              appId: r.appId,
              attributes: r.groupingAttributes,
              sortType: r.sortType,
            );
          } else
            return SplashScreen();
        },
        CommonConstants.projectListRoute: (context) {
          RouteParameters r = ModalRoute.of(context).settings.arguments;
          if (r != null && r.appId != null && r.appId.isNotEmpty) {
            return ProjectListScreen(
              appId: r.appId,
              sortType: r.sortType,
              groupingKey: r.groupingKey,
              groupingValue: r.groupingValue,
              projectMasterDataTableList: r.projectMasterDataTableList,
            );
          } else
            return SplashScreen();
        },
        CommonConstants.projectFormRoute: (context) {
          RouteParameters r = ModalRoute.of(context).settings.arguments;
          if (r != null && r.appId != null && r.appId.isNotEmpty) {
            return ProjectFormScreen(
              appId: r.appId,
              projectId: r.projectId,
              formActiontype: r.formActionType,
              projectMasterDataKeyToValueMap: r.projectFieldsKeyToValue,
            );
          } else
            return SplashScreen();
        },
        CommonConstants.getOTPRoute: (context) => GetOTPScreen(),
        CommonConstants.changePasswordRoute: (context) =>
            ChangePasswordScreen(),
        CommonConstants.userRegistrationRoute: (context) =>
            UserRegisterScreen(),
        CommonConstants.downloadsRoute: (context) => DownloadScreen(),
        CommonConstants.filterRoute: (context) {
          RouteParameters r = ModalRoute.of(context).settings.arguments;
          if (r != null && r.appId != null && r.appId.isNotEmpty) {
            return FilterScreen(
              appId: r.appId,
              projectList: UAAppContext.getInstance().projectList,
              filterKeyToValue:
                  UAAppContext.getInstance().filterSelectedValueMap,
            );
          } else
            return SplashScreen();
        },
        CommonConstants.geoTaggingRoute: (context) {
          RouteParameters r = ModalRoute.of(context).settings.arguments;
          if (r != null &&
              r.geoTaggingWidgetId != null &&
              r.geoTaggingWidgetId.isNotEmpty) {
            return GeotaggingWidget(
              ctxt: r.context,
              id: r.geoTaggingWidgetId,
              gpsValidation: r.gpsValidation,
              projLat: r.projLat,
              projLon: r.projLon,
            );
          } else
            return SplashScreen();
        },
        CommonConstants.profileRoute: (context) => UserProfileScreen(),
      },
      debugShowCheckedModeBanner: false,
      // theme: UniappColorTheme.defaultTheme,
      theme: UniappColorTheme.getTheme(),
      localizationsDelegates: [
        _newLocaleDelegate,
        //provides localised strings
        GlobalMaterialLocalizations.delegate,
        //provides RTL support
        GlobalWidgetsLocalizations.delegate,
      ],
      supportedLocales: [
        const Locale("en", ""),
        const Locale("hi", ""),
        const Locale("or", "")
      ],

    );
  }
}

这些是我在显示showVersionDialog()方法时得到的错误消息，而不是真正想要的。

E/flutter (12951): [ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: No MaterialLocalizations found.
E/flutter (12951): UniApp widgets require MaterialLocalizations to be provided by a Localizations widget ancestor.
E/flutter (12951): Localizations are used to generate many different messages, labels, and abbreviations which are used by the material library.
E/flutter (12951): To introduce a MaterialLocalizations, either use a MaterialApp at the root of your application to include them automatically, or add a Localization widget with a MaterialLocalizations delegate.
E/flutter (12951): The specific widget that could not find a MaterialLocalizations ancestor was:
E/flutter (12951):   UniApp
E/flutter (12951): The ancestors of this widget were:
E/flutter (12951):   [root]
E/flutter (12951): #0      debugCheckHasMaterialLocalizations.<anonymous closure> (package:flutter/src/material/debug.dart:72:7)
E/flutter (12951): #1      debugCheckHasMaterialLocalizations (package:flutter/src/material/debug.dart:92:4)
E/flutter (12951): #2      showDialog (package:flutter/src/material/dialog.dart:843:10)
E/flutter (12951): #3      _UniappMainState._showVersionDialog (package:Uniapp/main.dart:80:11)
E/flutter (12951): #4      _UniappMainState.versionCheck (package:Uniapp/main.dart:67:9)
E/flutter (12951): <asynchronous suspension>
E/flutter (12951): #5      _UniappMainState.initState (package:Uniapp/main.dart:44:5)

Answer 1

我只是通过创建一个带有变量的单例类(MySingletonClass)来解决这个问题。

 BuildContext get context => _context;

得到这个变量

 MySingletonClass.getInstance().context;

将单例类上下文传递给显示对话框contex

 final context = MySingletonClass.getInstance().context;
//calling showVersionDialong 
 _showVersionDialog(context);

Answer 2

在使用警报包显示弹出警报对话框时，我也遇到了类似的问题。我的代码结构是：

void main () {
    runApp(QuizPage)
}

在QuizPage内部，构建方法返回：

return MaterialApp(
        home: Scaffold())

我能够通过遵循本文中的说明中的第二个方法来解决这个问题：https://www.fluttercampus.com/guide/70/how-to-solve-no-materiallocalizations-found-error-exception-in-flutter/

现在我的代码结构是：

runApp(MaterialApp(home: MyApp()))

MyApp返回QuizPage