Flutter：将未来转换为流

Question

我正在从我的 json API 中获取作为 Future 的数据。并使用我的 Flutter Mobile 应用程序。

这是我从 API-

获取数据的代码

import 'dart:async';
import 'dart:convert';
import 'package:flutter/foundation.dart';
import 'package:http/http.dart' as http;

Future<List<Book>> fetchBooks(http.Client client) async {
  final response =
      await client.get('json URL');

  // Use the compute function to run parsePhotos in a separate isolate.
  return compute(parseBooks, response.body);
}

// A function that converts a response body into a List<Photo>.
List<Book> parseBooks(String responseBody) {
  final parsed = jsonDecode(responseBody).cast<String, dynamic>();
  return parsed['data'].map<Book>((json) => Book.fromJson(json)).toList();
}

class Book {
  final String name;
  final String author;
  final String genreClass;
  final String pdf;
  final int category;

  Book({
    this.name,
    this.author,
    this.genreClass,
    this.pdf,
    this.category,
  });

  factory Book.fromJson(Map<String, dynamic> json) {
    return Book(
      name: json['name'] as String,
      pdf: json['pdf'] as String,
      author: json['author'] as String,
      genreClass: json['genre_class'] as String,
      category: json['category'] as int,
    );
  }
}

但我想得到它，因为 Stream.Please 有人帮助我，我怎样才能将我的代码从 Future 转换为 Stream？

Answer 1

Abir Ahsan 试试这个，像这样调用（使用）你的函数：fetchBooks(client).asStream()...

Answer 2

如果您打算通过调用构建器函数获得动力。您将需要声明一个 StreamController，它创建一个可以被监听的简单流，并且您基本上使用接收器将事件流推送到流。一个简单的片段可以帮助每 3 秒显示一个滴答作响的加密货币价格：

StreamController<DataModel> _streamController = StreamController();
  @override
  void dispose() {
    // stop streaming when app close
    _streamController.close();
  }
  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    // A Timer method that run every 3 seconds
    Timer.periodic(Duration(seconds: 3), (timer) {
      getCryptoPrice();
    });
  }
  // a future method that fetch data from API
  Future<void> getCryptoPrice() async{
    var url = Uri.parse('https://api.nomics.com/v1/currencies/ticker?key=your_api_key&ids=DOGE');
    final response = await http.get(url);
    final databody = json.decode(response.body).first;
    DataModel dataModel = new DataModel.fromJson(databody);
    // add API response to stream controller sink
    _streamController.sink.add(dataModel);
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: StreamBuilder<DataModel>(
          stream: _streamController.stream,
          builder: (context,snapdata){
             switch(snapdata.connectionState){
               case ConnectionState.waiting: return Center(child: CircularProgressIndicator(),);
               default: if(snapdata.hasError){
                 return Text('Please Wait....');
               }else{
                 return Center(
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Text('${dataModel.name}',style: TextStyle(fontSize: 25),),
          SizedBox(height: 20,),
          SvgPicture.network('${dataModel.image}',width: 150,height: 150,),
          SizedBox(height: 20,),
          Text('$${dataModel.price}',style: TextStyle(fontSize: 20,fontWeight: FontWeight.bold),)
        ],
      ),
    );
               }
             }
          },
        ),
      ),
    );
  }

有关代码的更多信息：https://protocoderspoint.com/flutter-dart-stream-basic-example-fetch-crypto-currency-api-data/ 您可以了解更多：使用这些参考资料

Flutter：将未来转换为流

Flutter: convert future to stream

json

future

stream

flutter