Flutter: convert future to stream

Question

I am getting data as Future from my json API. And use my Flutter Mobile app.

Here is my code for getting data from API-

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,
    );
  }
}

But I want to get it as Stream.Please someone help me, how can I convert my code from Future to Stream ?

Answer 1

Abir Ahsan try this, call(use) your function like this : fetchBooks(client).asStream()...

Answer 2

If you're intend to get steam with your builder function is called. You will need to declare a StreamController, it creates a simple stream that can be listened to and you basically push streams of events to the stream, using the sink. A simple snippet can help in terms of displaying a ticking crypto price every 3 seconds:

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),)
        ],
      ),
    );
               }
             }
          },
        ),
      ),
    );
  }

More about the code here: https://protocoderspoint.com/flutter-dart-stream-basic-example-fetch-crypto-currency-api-data/ You can Learn more: using these references

1. https://dart.dev/articles/libraries/creating-streams#creating-a-stream-from-scratch
2. https://api.dart.dev/stable/2.16.2/dart-async/StreamController-class.html