isolate를 이용하여 데이터 처리하기

https://flutter.dev/docs/cookbook/networking/background-parsing

isolate 는  thread 임..

1. http 패키지 추가

https://pub.dev/packages/http

디펜더시 추가하기

dependencies:  http: ^0.12.2

라이브러리 임포트

import'package:http/http.dart'ashttp;

사용법

1. 기본

<생략>

2. 요청을 여러번 할 때

var client = http.Client(); try {   var uriResponse = await client.post('https://example.com/whatsit/create',       body: {'name': 'doodle', 'color': 'blue'});   print(await client.get(uriResponse.bodyFields['uri'])); } finally {   client.close(); }

2. 네트워크요청

Future<http.Response> fetchPhotos(http.Client client) async {

  return client.get('https://jsonplaceholder.typicode.com/photos');

}

url의(https://jsonplaceholder.typicode.com/photos)내용 중 일부.

{     "albumId": 1,     "id": 1,     "title": "accusamus beatae ad facilis cum similique qui sunt",     "url": "https://via.placeholder.com/600/92c952",     "thumbnailUrl": "https://via.placeholder.com/150/92c952"   },

이것을 저장하기 위한 Photo클래스

class Photo {
  final int albumId;
  final int id;
  final String title;
  final String url;
  final String thumbnailUrl;

  Photo({this.albumId, this.id, this.title, this.url, this.thumbnailUrl});

  factory Photo.fromJson(Map<String, dynamic> json) {
    return Photo(
      albumId: json['albumId'] as int,
      id: json['id'] as int,
      title: json['title'] as String,
      url: json['url'] as String,
      thumbnailUrl: json['thumbnailUrl'] as String,
    );
  }
}

3. JSON을 List<Photo>로 컨버팅 하기

List<Photo> parsePhotos(String responseBody){
  final parsed = jsonDecode(responseBody).cast<Map<String, dynamic>>();//cast는 빼도됨.
  return parsed.map<Photo>((json) => Photo.fromJson(json)).toList();

}


Future<List<Photo>> fetchPhotos(http.Client client) async {
  final response = await client.get('https://jsonplaceholder.typicode.com/photos');

  return parsePhotos(response.body);
}

4. isolate로 이동

compute()  는  spawn an isolate 함.

message 는 프리미티브 타입이거나 단순객체 이어야함. Futere 나 복잡한 개체는 안된다고함.

* 복잡한객체와 단순한 객체 차이점은 모르겟음

Future<List<Photo>> fetchPhotos(http.Client client) async {
  final response = await client.get('https://jsonplaceholder.typicode.com/photos');

  //return parsePhotos(response.body);
  return compute(parsePhotos, response.body);
}

5. 전체 소스

import 'dart:convert';

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


void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(primarySwatch: Colors.blue,
      ),
      home:MyHomepage()
    );
  }
}

class MyHomepage extends StatelessWidget{

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("My Home"),
      ),
      body: FutureBuilder<List<Photo>>(
        future: fetchPhotos(http.Client()),
        builder: (context, snapshot){
          if(snapshot.hasError){
            print(snapshot.error);
          }

          return snapshot.hasData
              ?PhotoList(photos:snapshot.data)
              :Center(child: CircularProgressIndicator());

        },

      ),
    );
  }
}

class PhotoList extends StatelessWidget{
  final List<Photo> photos;

  PhotoList({Key key, this.photos}) : super(key:key);

  @override
  Widget build(BuildContext context) {
    return GridView.builder(
      gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
        crossAxisCount: 2
      ),
      itemCount: photos.length,
      itemBuilder: (context, index){
        return Image.network(photos[index].thumbnailUrl);
      },
    );
  }
}


List<Photo> parsePhotos(String responseBody){
  final parsed = jsonDecode(responseBody).cast<Map<String, dynamic>>();//cast는 빼도됨.
  return parsed.map<Photo>((json) => Photo.fromJson(json)).toList();

}


Future<List<Photo>> fetchPhotos(http.Client client) async {
  final response = await client.get('https://jsonplaceholder.typicode.com/photos');

  //return parsePhotos(response.body);
  return compute(parsePhotos, response.body);
}


class Photo {
  final int albumId;
  final int id;
  final String title;
  final String url;
  final String thumbnailUrl;

  Photo({this.albumId, this.id, this.title, this.url, this.thumbnailUrl});

  factory Photo.fromJson(Map<String, dynamic> json) {
    return Photo(
      albumId: json['albumId'] as int,
      id: json['id'] as int,
      title: json['title'] as String,
      url: json['url'] as String,
      thumbnailUrl: json['thumbnailUrl'] as String,
    );
  }
}