目录

删除网络数据

目录

This recipe covers how to delete data over the internet using the http package.

This recipe uses the following steps:

  1. Add the http package.
  2. Delete data on the server.
  3. Update the screen.

1. Add the http package

#

To add the http package as a dependency, run flutter pub add:

flutter pub add http

Import the http package.

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

如果你要部署 Android，请编辑 AndroidManifest.xml 文件，添加 Internet 权限。

xml
<!-- Required to fetch data from the internet. -->
<uses-permission android:name="android.permission.INTERNET" />

同样，如果你要部署 macOS，请编辑 macos/Runner/DebugProfile.entitlements 和 macos/Runner/Release.entitlements 文件，添加 network client 权限。

xml
<!-- Required to fetch data from the internet. -->
<key>com.apple.security.network.client</key>
<true/>

2. Delete data on the server

#

This recipe covers how to delete an album from the JSONPlaceholder using the http.delete() method. Note that this requires the id of the album that you want to delete. For this example, use something you already know, for example id = 1.

dart
Future<http.Response> 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',
    },
  );

  return response;
}

The http.delete() method returns a Future that contains a Response.

  • Future is a core Dart class for working with async operations. A Future object represents a potential value or error that will be available at some time in the future.
  • The http.Response class contains the data received from a successful http call.
  • The deleteAlbum() method takes an id argument that is needed to identify the data to be deleted from the server.

3. Update the screen

#

In order to check whether the data has been deleted or not, first fetch the data from the JSONPlaceholder using the http.get() method, and display it in the screen. (See the Fetch Data recipe for a complete example.) You should now have a Delete Data button that, when pressed, calls the deleteAlbum() method.

dart
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());
        });
      },
    ),
  ],
);

Now, when you click on the Delete Data button, the deleteAlbum() method is called and the id you are passing is the id of the data that you retrieved from the internet. This means you are going to delete the same data that you fetched from the internet.

Returning a response from the deleteAlbum() method

#

Once the delete request has been made, you can return a response from the deleteAlbum() method to notify our screen that the data has been deleted.

dart
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) {
    // If the server did return a 200 OK response,
    // then return an empty Album. After deleting,
    // you'll get an empty JSON `{}` response.
    // Don't return `null`, otherwise `snapshot.hasData`
    // will always return false on `FutureBuilder`.
    return Album.empty();
  } else {
    // If the server did not return a "200 OK response",
    // then throw an exception.
    throw Exception('Failed to delete album.');
  }
}

FutureBuilder() now rebuilds when it receives a response. Since the response won't have any data in its body if the request was successful, the Album.fromJson() method creates an instance of the Album object with a default value (null in our case). This behavior can be altered in any way you wish.

That's all! Now you've got a function that deletes the data from the internet.

Complete example

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

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

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

  if (response.statusCode == 200) {
    // If the server did return a 200 OK response, then parse the JSON.
    return Album.fromJson(jsonDecode(response.body) as Map<String, dynamic>);
  } else {
    // If the server did not return a 200 OK response, then throw an exception.
    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) {
    // If the server did return a 200 OK response,
    // then return an empty Album. After deleting,
    // you'll get an empty JSON `{}` response.
    // Don't return `null`, otherwise `snapshot.hasData`
    // will always return false on `FutureBuilder`.
    return Album.empty();
  } else {
    // If the server did not return a "200 OK response",
    // then throw an exception.
    throw Exception('Failed to delete album.');
  }
}

class Album {
  int? id;
  String? title;

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

  Album.empty();

  factory Album.fromJson(Map<String, dynamic> json) {
    return switch (json) {
      {
        'id': int id,
        'title': String title,
      } =>
        Album(
          id: id,
          title: title,
        ),
      _ => throw const FormatException('Failed to load album.'),
    };
  }
}

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

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

  @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: 'Delete Data Example',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
      ),
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Delete Data Example'),
        ),
        body: Center(
          child: FutureBuilder<Album>(
            future: _futureAlbum,
            builder: (context, snapshot) {
              // If the connection is done,
              // check for response data or an error.
              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}');
                }
              }

              // By default, show a loading spinner.
              return const CircularProgressIndicator();
            },
          ),
        ),
      ),
    );
  }
}

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