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为ValueNotifier<LoadStatus>分派通知时引发以下NoSuchMethodError

flutter

Dolphin · 技术社区 · 4 年前

我正在使用fish redux在列表页中加载更多内容,这是刷新代码的一部分:

child: SmartRefresher(
                  onRefresh: () {
                    Future.delayed(Duration(milliseconds: 1000));
                    articleRequest.latestTime =
                        DateTime.now().millisecondsSinceEpoch;
                    _refreshController.refreshCompleted();
                  },
                  enablePullUp: true,
                  enablePullDown: true,
                  controller: _refreshController,
                  onLoading: () {
                    articleRequest.pageNum = articleRequest.pageNum + 1;
                    articleRequest.latestTime =
                        DateTime.now().millisecondsSinceEpoch;
                    dispatch(ChannelListDefaultActionCreator.onLoadingChannels(
                        articleRequest));

                    _refreshController.loadComplete();
                  },
}

SmartRefresher 组件加载事件时,我触发一个dispath以更改为组件状态,并从服务器触发一个新的获取请求。这是调度代码:

onLoading: () {
                        articleRequest.pageNum = articleRequest.pageNum + 1;
                        articleRequest.latestTime =
                            DateTime.now().millisecondsSinceEpoch;
                        dispatch(ChannelListDefaultActionCreator.onLoadingChannels(
                            articleRequest));
    
                        _refreshController.loadComplete();
                      }

这就是 action.dart 代码:

import 'package:Cruise/src/models/request/article/article_request.dart';
import 'package:fish_redux/fish_redux.dart';

//TODO replace with your own action
enum ChannelListDefaultAction { action, loading_channels }

class ChannelListDefaultActionCreator {
  static Action onAction() {
    return const Action(ChannelListDefaultAction.action);
  }

  static Action onLoadingChannels(ArticleRequest request) {
    return Action(ChannelListDefaultAction.loading_channels,payload: request);
  }
}

这就是 reducer.dart 代码:

import 'package:Cruise/src/models/request/article/article_request.dart';
import 'package:fish_redux/fish_redux.dart';

import 'action.dart';
import 'state.dart';

Reducer<ChannelListDefaultState> buildReducer() {
  return asReducer(
    <Object, Reducer<ChannelListDefaultState>>{
      ChannelListDefaultAction.action: _onAction,
      ChannelListDefaultAction.loading_channels: _onLoadingChannels,
    },
  );
}

ChannelListDefaultState _onAction(
    ChannelListDefaultState state, Action action) {
  final ChannelListDefaultState newState = state.clone();
  return newState;
}

ChannelListDefaultState _onLoadingChannels(
    ChannelListDefaultState state, Action action) {
  final ChannelListDefaultState newState = state.clone();
  ArticleRequest newReq = (action.payload as ArticleRequest);
  newState.articleRequest = newReq;
  return newState;
}

flutter: [debug] Capture from onError NoSuchMethodError: The method 'call' was called on null.
Receiver: null
Tried calling: call()

======== Exception caught by foundation library ====================================================
The following NoSuchMethodError was thrown while dispatching notifications for ValueNotifier<LoadStatus>:
The method 'call' was called on null.
Receiver: null
Tried calling: call()

When the exception was thrown, this was the stack: 
#0      ConnOp.set (package:fish_redux/src/redux_connector/connector.dart:19:43)
#1      MutableConn.subReducer.<anonymous closure> (package:fish_redux/src/redux/connector.dart:94:9)
#2      combineSubReducers.<anonymous closure> (package:fish_redux/src/redux/combine_reducers.dart:15:46)
#3      combineReducers.<anonymous closure> (package:fish_redux/src/redux/combine_reducers.dart:45:26)
#4      _appendUpdateStateReducer.<anonymous closure> (package:fish_redux/src/redux_component/batch_store.dart:100:44)
...
The ValueNotifier<LoadStatus> sending notification was: ValueNotifier<LoadStatus>#e760c(LoadStatus.loading)
====================================================================================================

我花了两天时间找出哪里出了问题。有人说我应该在连接器中实现set功能,然后我在连接器中添加了这个 ChannelListDefaultConnector :

@override
  void set(HomeListState state, ChannelListDefaultState subState) {
    state.channelListDefaultState = subState;
  }

但问题仍未解决。我应该怎么做来解决或避免这个问题?

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