Flutter的HTTP请求

忘是亡心i 2022-11-27 04:29 138阅读 0赞

It’s hard to do any sort of development without having to make some form of HTTP request, therefore, we’ll be looking at how to use the `http` plugin within Flutter.

无需进行某种形式的HTTP请求就很难进行任何类型的开发，因此，我们将研究如何在Flutter中使用`http`插件。

## 创建一个新的Flutter项目 **(**Creating a New Flutter Project**)** ##

In order to follow along with the setup we’ll be creating an example Flutter app. Assuming you already have the Flutter and Dart SDKs installed, run the following in your terminal:

为了进行设置，我们将创建一个Flutter应用示例。 假设您已经安装了Flutter和Dart SDK，请在终端中运行以下命令：

# New Flutter application
    $ flutter create flutter_http
    
    # Open this up inside of VS Code
    $ cd flutter_http && code .

## 添加HTTP插件 **(**Adding the HTTP plugin**)** ##

Head over to your `pubspec.yaml` and add the following plugin:

转到您的`pubspec.yaml`并添加以下插件：

dependencies:
      flutter:
        sdk: flutter
    
      http: ^0.12.0+2

This is an official Flutter plugin published by [dart.dev][] and it has [100 health score][], therefore, we can trust the reliability of this plugin.

这是由[dart.dev][]发布的官方Flutter插件，它的[运行状况得分为100][100 health score] ，因此，我们可以信赖该插件的可靠性。

## HTTP请求 **(**HTTP Requests**)** ##

Our first task will be to create a class which we can use to interact with our API. We’ll create a new class named `HttpService` at `lib/http_service.dart` and add a `getPosts` function:

我们的第一个任务是创建一个可用于与API交互的类。 我们将在`lib/http_service.dart`创建一个名为`HttpService`的新类，并添加一个`getPosts`函数：

class HttpService {
      final String postsURL = "https://jsonplaceholder.typicode.com/posts";
    
      Future<List<Post>> getPosts() async {
        Response res = await get(postsURL);
    
        if (res.statusCode == 200) {
          List<dynamic> body = jsonDecode(res.body);
    
          List<Post> posts = body
              .map(
                (dynamic item) => Post.fromJson(item),
              )
              .toList();
    
          return posts;
        } else {
          throw "Can't get posts.";
        }
      }
    }

As seen from the `getPosts` function, we’re firstly calling `get` from the `http` package on the `postsURL`.

从`getPosts`函数可以看出，我们首先从`postsURL`上的`http`包调用`get` 。

Next, if that request was successful, we’re parsing the response and returning a `List<Post>` using `Post.fromJson`. Let’s go ahead and create the `Post` class at `lib/posts_model.dart`:

接下来，如果请求成功，我们将解析响应并使用`Post.fromJson`返回`List<Post>` 。 让我们继续在`lib/posts_model.dart`创建`Post`类：

import 'package:flutter/foundation.dart';
    
    class Post {
      final int userId;
      final int id;
      final String title;
      final String body;
    
      Post({
        @required this.userId,
        @required this.id,
        @required this.title,
        @required this.body,
      });
    
      factory Post.fromJson(Map<String, dynamic> json) {
        return Post(
          userId: json['userId'] as int,
          id: json['id'] as int,
          title: json['title'] as String,
          body: json['body'] as String,
        );
      }
    }

In order to serialize the response, we’re returning a new `Post` with the `fromJson` method based on a JSON `Map`. In a production application, I’d recommend using something like [json\_serializable][json_serializable] to handle the serialization automatically.

为了序列化响应，我们将基于JSON `Map`使用`fromJson`方法返回一个新的`Post` 。 在生产应用程序中，建议使用[json\_serializable之][json_serializable]类的[东西][json_serializable]来自动处理序列化。

## 显示帖子 **(**Displaying Posts**)** ##

With this in mind, let’s create a new page named `PostsPage` at `lib/posts.dart`:

考虑到这一点，让我们在`lib/posts.dart`创建一个名为`PostsPage`的新页面：

import 'package:flut_http/http_service.dart';
    import 'package:flut_http/post_detail.dart';
    import 'package:flut_http/post_model.dart';
    import 'package:flutter/material.dart';
    
    class PostsPage extends StatelessWidget {
      final HttpService httpService = HttpService();
    
      @override
      Widget build(BuildContext context) {
        return Scaffold(
          appBar: AppBar(
            title: Text("Posts"),
          ),
          body: FutureBuilder(
            future: httpService.getPosts(),
            builder: (BuildContext context, AsyncSnapshot<List<Post>> snapshot) {
              if (snapshot.hasData) {
                List<Post> posts = snapshot.data;
                return ListView(
                  children: posts
                      .map(
                        (Post post) => ListTile(
                          title: Text(post.title),
                          subtitle: Text("${post.userId}"),
                          onTap: () => Navigator.of(context).push(
                            MaterialPageRoute(
                              builder: (context) => PostDetail(
                                post: post,
                              ),
                            ),
                          ),
                        ),
                      )
                      .toList(),
                );
              } else {
                return Center(child: CircularProgressIndicator());
              }
            },
          ),
        );
      }
    }

We’re using a `FutureBuilder` widget to interact with the `getPosts()` function. This allows us to determine when the `List<Post>` is ready and act accordingly.

我们正在使用`FutureBuilder`小部件与`getPosts()`函数进行交互。 这使我们能够确定`List<Post>` 何时准备就绪并采取相应措施。

If the `snapshot.hasData` is false, then we’re displaying the `CircularProgressIndicator`, otherwise we’re displaying the `ListTile` with various post information.

如果`snapshot.hasData`为false，则显示的是`CircularProgressIndicator` ， 否则显示的`ListTile`带有各种发布信息的`ListTile` 。

Let’s make sure we update `main.dart` with the `home` of `PostsPage`:

确保我们使用`main.dart`的`home`更新`PostsPage` ：

import 'package:flut_http/posts.dart';
    import 'package:flutter/material.dart';
    
    void main() => runApp(MyApp());
    
    class MyApp extends StatelessWidget {
      @override
      Widget build(BuildContext context) {
        return MaterialApp(
          title: 'HTTP',
          debugShowCheckedModeBanner: false,
          theme: ThemeData(
            primarySwatch: Colors.deepPurple,
          ),
          home: PostsPage(),
        );
      }
    }

## 帖子详细 **(**Post Detail**)** ##

If the user taps on the post, we’re looking to navigate the user away to a `PostDetail` page. Let’s build that:

如果用户点击该帖子，那么我们希望将其导航到`PostDetail`页面。 让我们来构建：

import 'package:flut_http/post_model.dart';
    import 'package:flutter/material.dart';
    
    class PostDetail extends StatelessWidget {
      final Post post;
    
      PostDetail({@required this.post});
    
      @override
      Widget build(BuildContext context) {
        return Scaffold(
            appBar: AppBar(
              title: Text(post.title),
            ),
            body: SingleChildScrollView(
              child: Padding(
                padding: const EdgeInsets.all(12.0),
                child: Column(
                  children: <Widget>[
                    Card(
                      child: Column(
                        crossAxisAlignment: CrossAxisAlignment.center,
                        children: <Widget>[
                          ListTile(
                            title: Text("Title"),
                            subtitle: Text(post.title),
                          ),
                          ListTile(
                            title: Text("ID"),
                            subtitle: Text("${post.id}"),
                          ),
                          ListTile(
                            title: Text("Body"),
                            subtitle: Text(post.body),
                          ),
                          ListTile(
                            title: Text("User ID"),
                            subtitle: Text("${post.userId}"),
                          ),
                        ],
                      ),
                    ),
                  ],
                ),
              ),
            ));
      }
    }

While this page doesn’t have any HTTP data, I’ve elected to add this to display the complete Post data.

虽然此页面没有任何HTTP数据，但我选择添加此数据以显示完整的Post数据。

## 删除 **(**DELETE**)** ##

Another example of such HTTP request is the use of the `delete` method. For example, inside of our `HttpService` we can create a `deletePost(int id)` method:

这种HTTP请求的另一个示例是`delete`方法的使用。 例如，在我们的`HttpService`内部，我们可以创建一个`deletePost(int id)`方法：

Future<void> deletePost(int id) async {
      Response res = await delete("$postsURL/$id");
    
      if (res.statusCode == 200) {
        print("DELETED");
      } else {
        throw "Can't delete post.";
      }
    }

We can add an `IconButton` to the `actions` array within the `AppBar` so that whenever this is tapped a `Post` is deleted:

我们可以在`AppBar`的`actions`数组中添加一个`IconButton` ，以便每当点击它时，就会删除一个`Post` ：

final HttpService httpService = HttpService();
    
    @override
    Widget build(BuildContext context) {
      return Scaffold(
          appBar: AppBar(
            title: Text(post.title),
            actions: <Widget>[
              IconButton(
                icon: Icon(Icons.delete),
                onPressed: () async {
                  await httpService.deletePost(post.id);
                  Navigator.of(context).pop();
                },
              )
            ],
          ),
        //
      )
    }

## 结语 **(**Wrapping Up**)** ##

In this article, we looked at how to interact with the Flutter `http` package. This allowed us to get a list of posts, as well as delete an individual post.

在本文中，我们研究了如何与Flutter `http`包进行交互。 这使我们能够获取帖子列表，以及删除单个帖子。

Similar operations such as `post`, `put`, `patch` and so on are also available. Check out the [documentation][] for more information on this.

也可以使用类似的操作，如`post` ， `put` ， `patch`等。 请查阅[文档][documentation]以获取更多信息。

> 翻译自: [https://www.digitalocean.com/community/tutorials/flutter-flutter-http][https_www.digitalocean.com_community_tutorials_flutter-flutter-http]

[dart.dev]: https://pub.dev/publishers/dart.dev/packages
[100 health score]: https://pub.dev/packages/http#-analysis-tab-
[json_serializable]: https://pub.dev/packages/json_serializable
[documentation]: https://pub.dev/documentation/http/latest/http/http-library.html
[https_www.digitalocean.com_community_tutorials_flutter-flutter-http]: https://www.digitalocean.com/community/tutorials/flutter-flutter-http