是什么导致应用卡在启动屏幕上

如何解决是什么导致应用卡在启动屏幕上

当我尝试运行该应用程序时，它似乎停留在加载屏幕上，如下所示：

[！[在此处输入图片描述] [1]] [1] [1]：https：//i.stack.imgur.com/bbCpS.png

调试控制台输出将显示以下消息：

D/EGL_emulation( 6100): eglMakeCurrent: 0xe775f640: ver 2 0 (tinfo 0xe8973f60)
D/eglCodecCommon( 6100): setVertexArrayObject: set vao to 0 (0) 1 0
I/flutter ( 6100): Log [base_url: https://markets.smartersvision.com/] | (main (package:markets/main.dart:16:32))
I/flutter ( 6100): Log [api_base_url: https://markets.smartersvision.com/api/] | (main (package:markets/main.dart:18:32))
Reloaded 1 of 1484 libraries in 555ms.
I/flutter ( 6100): Log [https://markets.smartersvision.com/api/settings] | (initSettings (package:markets/src/repository/settings_repository.dart:46:34))
I/flutter ( 6100): NoSuchMethodError: The getter 'length' was called on null.
I/flutter ( 6100): Receiver: null

这是main.dart文件中的相应代码：

import 'package:flutter/material.dart';
import 'package:flutter_localizations/flutter_localizations.dart';
import 'package:global_configuration/global_configuration.dart';

import 'generated/l10n.dart';
import 'route_generator.dart';
import 'src/helpers/app_config.dart' as config;
import 'src/helpers/custom_trace.dart';
import 'src/models/setting.dart';
import 'src/repository/settings_repository.dart' as settingRepo;
import 'src/repository/user_repository.dart' as userRepo;

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await GlobalConfiguration().loadFromAsset("configurations");
  print(CustomTrace(StackTrace.current,message: "base_url: ${GlobalConfiguration().getString('base_url')}"));
  print(CustomTrace(StackTrace.current,message:
          "api_base_url: ${GlobalConfiguration().getString('api_base_url')}"));
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  // This widget is the root of your application.
//  /// Supply 'the Controller' for this application.
//  MyApp({Key key}) : super(con: Controller(),key: key);

  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  @override
  void initState() {
    settingRepo.initSettings();
    settingRepo.getCurrentLocation();
    userRepo.getCurrentUser();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return ValueListenableBuilder(
        valueListenable: settingRepo.setting,builder: (context,Setting _setting,_) {
          return MaterialApp(
              navigatorKey: settingRepo.navigatorKey,title: _setting.appName,initialRoute: '/Splash',onGenerateRoute: RouteGenerator.generateRoute,debugShowCheckedModeBanner: false,locale: _setting.mobileLanguage.value,localizationsDelegates: [
                S.delegate,GlobalMaterialLocalizations.delegate,GlobalWidgetsLocalizations.delegate,],supportedLocales: S.delegate.supportedLocales,theme: _setting.brightness.value == Brightness.light
                  ? ThemeData(

并在settings_repository.dart文件中：

import 'dart:async';
import 'dart:convert';
import 'dart:io';

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:global_configuration/global_configuration.dart';
import 'package:google_maps_flutter/google_maps_flutter.dart';
import 'package:http/http.dart' as http;
import 'package:location/location.dart';
import 'package:shared_preferences/shared_preferences.dart';

import '../helpers/custom_trace.dart';
import '../helpers/maps_util.dart';
import '../models/address.dart';
import '../models/setting.dart';

ValueNotifier<Setting> setting = new ValueNotifier(new Setting());
ValueNotifier<Address> deliveryAddress = new ValueNotifier(new Address());
final navigatorKey = GlobalKey<NavigatorState>();
//LocationData locationData;

Future<Setting> initSettings() async {
  Setting _setting;
  final String url =
      '${GlobalConfiguration().getString('api_base_url')}settings';
  try {
    final response = await http
        .get(url,headers: {HttpHeaders.contentTypeHeader: 'application/json'});
    if (response.statusCode == 200 &&
        response.headers.containsValue('application/json')) {
      if (json.decode(response.body)['data'] != null) {
        SharedPreferences prefs = await SharedPreferences.getInstance();
        await prefs.setString(
            'settings',json.encode(json.decode(response.body)['data']));
        _setting = Setting.fromJSON(json.decode(response.body)['data']);
        if (prefs.containsKey('language')) {
          _setting.mobileLanguage.value = Locale(prefs.get('language'),'');
        }
        _setting.brightness.value = prefs.getBool('isDark') ?? false
            ? Brightness.dark
            : Brightness.light;
        setting.value = _setting;
        // ignore: invalid_use_of_visible_for_testing_member,invalid_use_of_protected_member
        setting.notifyListeners();
      }
    } else {
      print(CustomTrace(StackTrace.current,message: response.body).toString());
    }
  } catch (e) {
    print(CustomTrace(StackTrace.current,message: url).toString());
    return Setting.fromJSON({});
  }
  return setting.value;
}

有人知道这是什么原因吗？

解决方法

我前一段时间遇到此错误，要解决此问题，建议您确保已安装接收器。 对您的项目特别有用：您的length属性值为null，因此请确保小部件的长度值已设置。