如何取消或伪取消http请求？- 颤振

Question

我有一个搜索栏，当输入字符时，它会向 BLoC 发送请求，然后 BLoC 从 Future 请求数据。

这是 BLoC

import 'dart:async';

import 'package:bloc/bloc.dart';
import 'package:equatable/equatable.dart';
import 'package:stockrails/models/semantics/error-type-model.dart';
import 'package:stockrails/models/user-interface/search-query-model.dart';
import 'package:stockrails/services/apis/stock-data.dart';
import 'package:stockrails/shared/constants/messages.dart';

part 'search_event.dart';
part 'search_state.dart';

class SearchBloc extends Bloc<SearchEvent, SearchState> {
  SearchBloc() : super(SearchInitial());

  // Connection to api service
  StockData _data = StockData();

  @override
  Stream<SearchState> mapEventToState(
    SearchEvent event,
  ) async* {
    // : Initial search state - no text has been entered, no loading
    if (event is SearchIntializeEvent) {
      yield SearchInitial();
    }
    // : Querying search state - text is being entered, loading next
    if (event is SearchQueryingEvent) {
      // Yields call
      yield* _mapAPICallToEvent(event.query);
    }
  }

  // + ----------- Functions -------------

  Stream<SearchState> _mapAPICallToEvent(String query) async* {
    // : Yield loading screen based on prior state
    if (state is SearchErrorState)
      yield SearchErrorLoadingState();
    else
      yield SearchLoadingState(query: query);

    // : Attempts to call method
    List<SearchQueryModel> _result;

    try {
      _result = await _data.searchQuery(query);
    } on TimeoutException {
      _result = null;
    } catch (err) {
      _result = [];
    }

    // : If it can't then it defaults to using the unknownErrorMessage
    if (_result == null)
      yield SearchErrorState(errorMessage: Messages.unknownErrorMessage, errorType: ErrorType.errorTypes[0]);

    // : Else if there's no content in the response
    else if (_result.length == 0)
      yield SearchErrorState(errorMessage: query, errorType: ErrorType.errorTypes[1]);

    // : If there's no errors return loaded!
    else {
      yield SearchLoadedState(searchQueryModelList: _result, query: query);
    }
  }
}

这就是获取数据的未来

  // Grabs data from endpoint and returns or errors
  // If it times out it will throw a TimeoutException
  Future _dataFetch(String url, String query, String token) async {
    try {
      // Build out auth header
      final authHeader = 'Bearer $token';

      final response = await http
          .get(url, headers: <String, String>{
            'query': query,
            'authorization': authHeader,
          })
          .timeout(Duration(seconds: 10))
          .catchError((error) {
            throw error;
          });

      // Makes sure response is okay
      if (response.statusCode == 200) {
        return json.decode(response.body);
      }

      // If status code is unknown, prints an error
      else {
        throw Exception(Messages.unknownErrorMessage);
      }
    } on TimeoutException catch (error) {
      throw error;
    } on SocketException catch (error) {
      throw error;
    } catch (error) {
      throw error;
    }
  }

---

我一直在绞尽脑汁，试图找到一个解决方案，await既可以为未来打造 BLoC，又可以SearchInitializeEvent取消任何正在提出的请求。

因为发生的情况是在一个糟糕的网络上发生的，所以无论如何，请求都会尝试通过，并且在得到响应之前不会停止。

我知道你不能取消期货，我尝试了两者CancelableOperation或CancelableCompletion无论它被称为什么。

我猜我必须将我的 Future 设置为 Stream，这样我才能关闭它。我愿意接受任何建议。先感谢您！

Answer 1

dart 在破坏 Stream 方面存在限制。这是在“循环”之外无法完成的事情。这个问题在这里进行了详细讨论：

https://github.com/dart-lang/sdk/issues/42717

https://github.com/felangel/bloc/issues/1472

您可能想从不同的角度来研究这个问题，例如覆盖最近请求所做的更改。或者，如果请求结果显示在屏幕上，则考虑不显示结果。