Flutter 如何将 BLoC 旧版本代码迁移到 Bloc 8.0.1 版本答案

【问题标题】：Flutter how to migrate BLoC old version code to Bloc 8.0.1 versionFlutter 如何将 BLoC 旧版本代码迁移到 Bloc 8.0.1 版本
【发布时间】：2022-01-10 08:10:58
【问题描述】：

在研究 Bloc 从旧版本迁移到新 8 时。我无法修复转换到新版本。我遇到了许多我没有弄清楚的未定义的事情。

import 'dart:async';

import 'package:WeatherApp/events/WeatherEvent.dart';
import 'package:WeatherApp/models/Weather.dart';
import 'package:WeatherApp/services/WeatherService.dart';
import 'package:WeatherApp/states/WeatherState.dart';
import 'package:bloc/bloc.dart';
import 'package:geolocator/geolocator.dart';

class WeatherBloc extends Bloc<WeatherEvent, WeatherState> {
  WeatherBloc() : super(null) {
    add(WeatherCurrentPositionRequested());
  }

  @override
  Stream<WeatherState> mapEventToState(WeatherEvent event) async* {
    if (event is WeatherRequested) {
      yield* _newWeatherRequested(event);
    }
    if (event is WeatherCurrentPositionRequested) {
      yield* _newWeatherCurrentPositionRequested();
    }
  }

  Stream<WeatherState> _newWeatherRequested(WeatherRequested event) async* {
    yield WeatherLoadInProgress();
    try {
      final Weather weather = await WeatherService.fetchCurrentWeather(
          query: event.city, lon: event.lon, lat: event.lat);
      final List<Weather> hourlyWeather =
          await WeatherService.fetchHourlyWeather(
              query: event.city, lon: event.lon, lat: event.lat);
      yield WeatherLoadSuccess(weather: weather, hourlyWeather: hourlyWeather);
    } catch (e) {
      yield WeatherLoadFailure();
    }
  }

  Stream<WeatherState> _newWeatherCurrentPositionRequested() async* {
    LocationPermission permission = await checkPermission();
    if (permission == LocationPermission.whileInUse ||
        permission == LocationPermission.always) {
      Position lastKnownPosition = await getLastKnownPosition();
      if(lastKnownPosition != null) {
        add(WeatherRequested(
            lat: lastKnownPosition.latitude.toString(),
            lon: lastKnownPosition.longitude.toString()));

      } else {
        Position position =
        await getCurrentPosition(desiredAccuracy: LocationAccuracy.high);
        add(WeatherRequested(
            lat: position.latitude.toString(),
            lon: position.longitude.toString()));
      }
    } else {
      await requestPermission();
      add(WeatherCurrentPositionRequested());
    }
  }
}

https://github.com/evgenusov/FlutterWeatherApp/blob/master/lib/bloc/WeatherBloc.dart

【问题讨论】：

标签： flutter migration bloc flutter-bloc

【解决方案1】：

这应该可行。

您还需要将 Flutter bloc 依赖项更改为最新的才能完成这项工作。

import 'package:WeatherApp/events/WeatherEvent.dart';
import 'package:WeatherApp/models/Weather.dart';
import 'package:WeatherApp/services/WeatherService.dart';
import 'package:WeatherApp/states/WeatherState.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:geolocator/geolocator.dart';

class WeatherBloc extends Bloc<WeatherEvent, WeatherState> {
  WeatherBloc() : super(WeatherInitial()) {
    on<WeatherRequested>((event, emit) async {
      emit(WeatherLoadInProgress());
      try {
        final Weather weather = await WeatherService.fetchCurrentWeather(
            query: event.city, lon: event.lon, lat: event.lat);
        final List<Weather> hourlyWeather =
            await WeatherService.fetchHourlyWeather(
                query: event.city, lon: event.lon, lat: event.lat);
        emit(
            WeatherLoadSuccess(weather: weather, hourlyWeather: hourlyWeather));
      } catch (e) {
        emit(WeatherLoadFailure());
      }
    });

    on<WeatherCurrentPositionRequested>((event, emit) async {
      LocationPermission permission = await Geolocator.checkPermission();
      if (permission == LocationPermission.whileInUse ||
          permission == LocationPermission.always) {
        Position lastKnownPosition = await Geolocator.getLastKnownPosition();
        if (lastKnownPosition != null) {
          add(WeatherRequested(
              lat: lastKnownPosition.latitude.toString(),
              lon: lastKnownPosition.longitude.toString()));
        } else {
          Position position = await Geolocator.getCurrentPosition(
              desiredAccuracy: LocationAccuracy.high);
          add(WeatherRequested(
              lat: position.latitude.toString(),
              lon: position.longitude.toString()));
        }
      } else {
        await Geolocator.requestPermission();
        add(WeatherCurrentPositionRequested());
      }
    });
  }
}

bloc 提供者需要以下签名才能工作。

BlocProvider(
  create: (context) => WeatherBloc()
    ..add(
      WeatherCurrentPositionRequested(),
    ),
  child: ... your code
),

【讨论】：