颤振块；预期有 1 个位置参数，但找到了 0 个

Question

颤振版本：2.1.0

Flutter Bloc 版本：^7.0.1

飞镖：2.13.0

出现此错误：预期有 1 个位置参数，但找到了 0 个。尝试添加缺少的arguments.dart(not_enough_positional_arguments)。

我有什么错吗

我的侧边栏布局发生错误的位置：

 body: BlocProvider<NavigationBloc>(
        create: (context) => NavigationBloc(),
        child: Stack(
          children: [
            BlocBuilder<NavigationBloc, NavigationStates>(
                builder: (context, NavigationState) {
              return NavigationState as Widget;
            }),
            SideBar(),
          ],
        ),
      ),

我的区块导航文件：

import '/Pages/DeviceLocation/DeviceLocation.dart';

import '/Pages/Devices/DeviceLanding.dart';

import '../../LandingScreen/components/body.dart';
import '../../SensorScreen/charts/GasChart.dart';
import '../../SensorScreen/charts/HumChart.dart';
import '../../SensorScreen/charts/MoisChart.dart';
import '../../SensorScreen/charts/NurChart.dart';
import '../../SensorScreen/charts/PhChart.dart';
import '../../SensorScreen/charts/TemChart.dart';
import '../../SensorScreen/charts/chartComponents/NurCard.dart';
import 'package:bloc/bloc.dart';

enum NavigationEvents {
  // DashboardClickEvent,
  LandingScreenBodyClickEvent,
  TemChartClickEvent,
  HumChartClickEvent,
  MoisChartClickEvent,
  PhChartClickEvent,
  NurChartClickEvent,
  GasChartClickEvent,
  DevicesClickEvent,
  DevicesLocationClickEvent,
  AccountClickEvent,
  SettingsClickEvent
}

abstract class NavigationStates {}

class NavigationBloc extends Bloc<NavigationEvents, NavigationStates> {
  NavigationBloc(NavigationStates initialState) : super(initialState);

  @override
  NavigationStates get initialState => LandingScreenBody();

  @override
  Stream<NavigationStates> mapEventToState(NavigationEvents event) async* {
    switch (event) {
      case NavigationEvents.LandingScreenBodyClickEvent:
        yield LandingScreenBody();
        break;
      case NavigationEvents.TemChartClickEvent:
        yield TemChart();
        break;
      case NavigationEvents.HumChartClickEvent:
        yield HumChart();
        break;
      case NavigationEvents.MoisChartClickEvent:
        yield MoisChart();
        break;
      case NavigationEvents.PhChartClickEvent:
        yield PhChart();
        break;
      case NavigationEvents.NurChartClickEvent:
        yield NurChart();
        break;
      case NavigationEvents.GasChartClickEvent:
        yield GasChart();
        break;
      case NavigationEvents.DevicesClickEvent:
        yield DeviceLanding();
        break;
      case NavigationEvents.DevicesLocationClickEvent:
        yield DevicesLocation();
        break;
    }
  }
}

我在做什么？

Answer 1

您不必将状态传递给块构造函数，这应该可以工作

NavigationBloc() : super(LandingScreenBody());

在 flutter_bloc 7.0.0 中，不再有

initialState

getter，所以你也必须删除它

Answer 2

您遇到的错误是因为 NavigationBloc 的构造函数需要一个位置参数，但您没有将其传入。具体来说，您的 NavigationBloc 构造函数需要一个初始状态 (NavigationStates initialState)，但在实例化 NavigationBloc 时缺少该状态。 任何继承自 NavigationStates 的状态都可以作为参数传递。在本例中，我使用 LandingScreenBody() 作为初始状态的示例。

NavigationBloc(LandingScreenBody()),

因此，您更新后的代码将如下所示：

BlocProvider<NavigationBloc>(
  create: (context) => NavigationBloc(LandingScreenBody()), // Pass the initial state
  child: Stack(
    children: [
      BlocBuilder<NavigationBloc, NavigationStates>(
        builder: (context, NavigationState) {
          return NavigationState as Widget;
        },
      ),
      SideBar(),
    ],
  ),
),