[Cookbook] Networking - 데이터 삭제

요약

http package를 이용해서 data 삭제

 

전체 과정

1. http Package 추가

2. Server에서의 data 삭제

3. Screen 업데이트

 

상세 과정

1. http Package 추가

- pubspec.yaml 파일의 dependency 에 http 추가

- import 'package:http/http.dart' as http;

 

2. http.delete() method

- http.delete() method는 Response를 포함하고 있는 Future를 반환

- Future는 async 동작에 사용되는 중요한 클래스 (Potential 값 및 error를 저장할 수 있는 객체)

- Future<http.response> / Uri.parse를 통해서, URL을 입력 / header도 별도로 추가해주기

Future<http.Response> deleteAlbum(String id) async {
  final http.Response response = await http.delete(
    Uri.parse('http://jsonplaceholder.typicode.com/albums/$id'),
    headers: <String, String> {
      'Content-Type': 'application/json; charset=UTF-8',
    },
  );
  return response;
}

3. update the screen

- data를 삭제한 후에 setState를 통해서 상태를 업데이트 해줌

- 이 예제의 경우 화면에 표시된 id를 활용하는 경우가 있는데, snapshot을 활용

Column(
	mainAxisAlignment: MainAxisAlignment.center,
    children: <Widget>[
        // snapshot.data?.title ?? 'Deleted' : null이면 'Deleted'를 입력하라.
        // snapshot : JSON 형태의 Object를 쉽게 접근할 수 있도록 해주는 library
    	Text(snapshot.data?.title ?? 'Deleted'),
        ElevatedButton(
        	child: const Text('Delete Data'),
            onPressed: () {
            	setState(() {
                	_futureAlbum =
                    	deleteAlbum(snapshot.data!.id.toString());
                });
            },
        ),
   ]
);

 

4. Returning a response

- Album.fromJson(jsonDecode(response.body));

- if (response.stautsCode == 200)

- throw Exception('Failed to delete album')

Future<Album> deleteAlbum(String id) async {
  final http.Response response = await http.delete(
    Uri.parse('https://jsonplaceholder.typicode.com/albums/$id'),
    headers: <String, String>{
      'Content-Type': 'application/json; charset=UTF-8',
    },
  );

  if (response.statusCode == 200) {
    return Album.fromJson(jsonDecode(response.body));
  } else {
    throw Exception('Failed to delete album.');
  }
}

 

[Complete Example]

- CircularProgressIndicator();

- factory Album.fromJson(Map<String, dynamic> json)

 

import 'dart:async';
import 'dart:convert';

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

void main() => runApp(const MyApp());

class MyApp extends StatefulWidget{
  const MyApp({super.key});

  @override
  // in case of StatefulWidget
  // 'createState()' Method needs to be override.
  State<MyApp> createState() {
    return _MyAppState();
  }
}

class _MyAppState extends State<MyApp> {
  late Future<Album> _futureAlbum;

  @override
  void initState() {
    super.initState();
    _futureAlbum = fetchAlbum();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Deleting Data Example',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Delete Data Example'),
        ),
        body: Center(
          child: FutureBuilder<Album>(
            future: _futureAlbum,
            builder: (context, snapshot) {
              if (snapshot.connectionState == ConnectionState.done) {
                if (snapshot.hasData) {
                  return Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: <Widget>[
                      Text(snapshot.data?.title ?? "Deleted"),
                      ElevatedButton(
                        child: const Text('Delete Data'),
                        onPressed: () {
                          setState(() {
                            _futureAlbum =
                                deleteAlbum(snapshot.data!.id.toString());
                          });
                        },
                      ),
                    ],
                  );
                } else if (snapshot.hasError) {
                  return Text('${snapshot.error}');
                }
              }
              return const CircularProgressIndicator();
            }
          ),
        ),
      ),
    );
  }
}

class Album {
    final int? id;
    final String? title;

    const Album({this.id, this.title});

    factory Album.fromJson(Map<String, dynamic> json) {
      return Album(
        id: json['id'],
        title: json['title'],
      );
    }
}

Future<Album> fetchAlbum() async {
    final response = await http.get(
      Uri.parse('https://jsonplaceholder.typicode.com/albums/1'),
    );

    if (response.statusCode == 200) {
      return Album.fromJson(jsonDecode(response.body));
    } else {
      throw Exception('Failed to load album');
    }
}

Future<Album> deleteAlbum(String id) async {
  final http.Response response = await http.delete(
    Uri.parse('https://jsonplaceholder.typicode.com/albums/$id'),
    headers: <String, String> {
      'Content-Type': 'application/json; charset=UTF-8',
    },
  );

  if (response.statusCode == 200) {
    return Album.fromJson(jsonDecode(response.body));
  } else {
    throw Exception('Failed to delete album.');
  }
}

 

All the contents comes from the official Flutter Document (cookbook)

https://docs.flutter.dev/cookbook/networking/delete-data