ReactiveX 学习笔记（15）使用 Rx.NET + Json.NET 调用 REST API

JSON : Placeholder

JSON : Placeholder (https://jsonplaceholder.typicode.com/) 是一个用于测试的 REST API 网站。
以下使用 Task API/Rx.NET + Json.NET 调用该网站的 REST API，获取字符串以及 JSON 数据。

• GET /posts/1
• GET /posts
• POST /posts
• PUT /posts/1
• DELETE /posts/1

所有 GET API 都返回JSON数据，格式（JSON-Schema）如下：

{
  "type":"object",
  "properties": {
    "userId": {"type" : "integer"},
    "id": {"type" : "integer"},
    "title": {"type" : "string"},
    "body": {"type" : "string"}
  }
}

Post 对象

public class Post
{
    [JsonProperty("userId")]
    public int UserId { get; set; }
    [JsonProperty("id")]
    public int Id { get; set; }
    [JsonProperty("title")]
    public string Title { get; set; }
    [JsonProperty("body")]
    public string Body { get; set; }

    public override string ToString() =>
        $"Post {{userId = {UserId}, id = {Id}, title = "{Title}", body = "{Body.Replace("
", "\n")}"}}";
}

Post 对象负责 .NET 对象和 JSON 数据的相互转换。
Post 类使用了 Json.NET 所提供的 attributes。

Task API

public class PostDataStoreByTask
{
    protected HttpClient client = new HttpClient
    {
        BaseAddress = new Uri("https://jsonplaceholder.typicode.com/")
    };

    public async Task<string> GetPostAsString(int id) =>
    !CrossConnectivity.Current.IsConnected ? null : await client.GetStringAsync($"posts/{id}");

    public async Task<Post> GetPostAsJson(int id)
    {
        if (!CrossConnectivity.Current.IsConnected) return null;

        var json = await client.GetStringAsync($"posts/{id}");
        var item = await Task.Run(() => JsonConvert.DeserializeObject<Post>(json));

        return item;
    }

    public async Task<IEnumerable<Post>> GetPosts(int n)
    {
        IEnumerable<Post> items = new List<Post>();
        if (CrossConnectivity.Current.IsConnected)
        {
            var json = await client.GetStringAsync("posts");
            items = await Task.Run(() => JsonConvert.DeserializeObject<IEnumerable<Post>>(json));
        }
        return items.Take(n);
    }

    private StringContent GetStringContent(Post item) =>
    new StringContent(JsonConvert.SerializeObject(item), Encoding.UTF8, "application/json");

    public async Task<Post> CreatePost(Post item)
    {
        if (item == null || !CrossConnectivity.Current.IsConnected) return null;

        var response = await client.PostAsync("posts", GetStringContent(item));
        if (!response.IsSuccessStatusCode) return null;

        var json = await response.Content.ReadAsStringAsync();
        var item2 = await Task.Run(() => JsonConvert.DeserializeObject<Post>(json));

        return item2;
    }

    public async Task<Post> UpdatePost(Post item)
    {
        if (item == null || !CrossConnectivity.Current.IsConnected) return null;

        var response = await client.PutAsync($"posts/{item.Id}", GetStringContent(item));
        if (!response.IsSuccessStatusCode) return null;

        var json = await response.Content.ReadAsStringAsync();
        var item2 = await Task.Run(() => JsonConvert.DeserializeObject<Post>(json));

        return item2;
    }

    public async Task<string> DeletePost(int id)
    {
        if (!CrossConnectivity.Current.IsConnected) return null;

        var response = await client.DeleteAsync($"posts/{id}");
        if (!response.IsSuccessStatusCode) return null;

        var json = await response.Content.ReadAsStringAsync();
        return json;
    }
}

• getPostAsString 方法取出第1个Post，返回字符串
• getPostAsJson 方法取出第1个Post，返回Post对象
• getPosts 方法取出前n个Post，返回n个Post对象
• createPost 方法创建1个Post，返回所创建的Post对象
• updatePost 方法更新第1个Post，返回所更新的Post对象
• deletePost 方法删除第1个Post，返回字符串

Rx.NET

public class PostDataStoreByRx
{
    protected HttpClient client = new HttpClient
    {
        BaseAddress = new Uri("https://jsonplaceholder.typicode.com/")
    };

    public IObservable<string> GetPostAsString(int id) =>
    !CrossConnectivity.Current.IsConnected ? Observable.Empty<string>() :
        client.GetStringAsync($"posts/{id}").ToObservable();

    public IObservable<Post> GetPostAsJson(int id) =>
    !CrossConnectivity.Current.IsConnected? Observable.Empty<Post>() :
        client.GetStringAsync($"posts/{id}").ToObservable()
        .Select(json => JsonConvert.DeserializeObject<Post>(json));

    public IObservable<Post> GetPosts(int n) =>
    !CrossConnectivity.Current.IsConnected ? Observable.Empty<Post>() :
        client.GetStringAsync("posts").ToObservable()
        .SelectMany(json => JsonConvert.DeserializeObject<IEnumerable<Post>>(json))
        .Take(n);

    private StringContent GetStringContent(Post item) =>
    new StringContent(JsonConvert.SerializeObject(item), Encoding.UTF8, "application/json");

    public IObservable<Post> CreatePost(Post item) =>
    item == null || !CrossConnectivity.Current.IsConnected ? Observable.Empty<Post>() :
        client.PostAsync("posts", GetStringContent(item)).ToObservable()
        .SelectMany(response => !response.IsSuccessStatusCode ? Observable.Empty<Post>() :
            response.Content.ReadAsStringAsync().ToObservable()
            .Select(json => JsonConvert.DeserializeObject<Post>(json)));

    public IObservable<Post> UpdatePost(Post item) =>
    item == null || !CrossConnectivity.Current.IsConnected? Observable.Empty<Post>() :
        client.PutAsync($"posts/{item.Id}", GetStringContent(item)).ToObservable()
        .SelectMany(response => !response.IsSuccessStatusCode? Observable.Empty<Post>() :
            response.Content.ReadAsStringAsync().ToObservable()
            .Select(json => JsonConvert.DeserializeObject<Post>(json)));

    public IObservable<string> DeletePost(int id) =>
    !CrossConnectivity.Current.IsConnected ? Observable.Empty<string>() :
        client.DeleteAsync($"posts/{id}").ToObservable()
        .SelectMany(response => !response.IsSuccessStatusCode ? Observable.Empty<string>() :
            response.Content.ReadAsStringAsync().ToObservable());
}

相比较 Task API，Rx.NET 代码简练但是比较难理解。

Main 方法

public static void Main(string[] args)
{
    {
        var dataStore = new PostDataStoreByTask();
        Console.WriteLine(dataStore.GetPostAsString(1).Result);
        Console.WriteLine(dataStore.GetPostAsJson(1).Result);
        dataStore.GetPosts(2).Result.ToList().ForEach(Console.WriteLine);
        Console.WriteLine(dataStore.CreatePost(new Post
        {
            UserId = 101,
            Id = 0,
            Title = "test title",
            Body = "test body"
        }).Result);
        Console.WriteLine(dataStore.UpdatePost(new Post
        {
            UserId = 101,
            Id = 1,
            Title = "test title",
            Body = "test body"
        }).Result);
        Console.WriteLine(dataStore.DeletePost(1).Result);
    }
    {
        var dataStore = new PostDataStoreByRx();
        dataStore.GetPostAsString(1).Subscribe(Console.WriteLine);
        dataStore.GetPostAsJson(1).Subscribe(Console.WriteLine);
        dataStore.GetPosts(2).Do(Console.WriteLine).Subscribe();
        dataStore.CreatePost(new Post
        {
            UserId = 101,
            Id = 0,
            Title = "test title",
            Body = "test body"
        }).Subscribe(Console.WriteLine);
        dataStore.UpdatePost(new Post
        {
            UserId = 101,
            Id = 1,
            Title = "test title",
            Body = "test body"
        }).Subscribe(Console.WriteLine);
        dataStore.DeletePost(1).Subscribe(Console.WriteLine);
        Console.ReadKey();
    }
}

输出结果

{
  "userId": 1,
  "id": 1,
  "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
  "body": "quia et suscipit
suscipit recusandae consequuntur expedita et cum
reprehenderit molestiae ut ut quas totam
nostrum rerum est autem sunt rem eveniet architecto"
}
Post {userId = 1, id = 1, title = "sunt aut facere repellat provident occaecati excepturi optio reprehenderit", body = "quia et suscipit
suscipit recusandae consequuntur expedita et cum
reprehenderit molestiae ut ut quas totam
nostrum rerum est autem sunt rem eveniet architecto"}
Post {userId = 1, id = 1, title = "sunt aut facere repellat provident occaecati excepturi optio reprehenderit", body = "quia et suscipit
suscipit recusandae consequuntur expedita et cum
reprehenderit molestiae ut ut quas totam
nostrum rerum est autem sunt rem eveniet architecto"}
Post {userId = 1, id = 2, title = "qui est esse", body = "est rerum tempore vitae
sequi sint nihil reprehenderit dolor beatae ea dolores neque
fugiat blanditiis voluptate porro vel nihil molestiae ut reiciendis
qui aperiam non debitis possimus qui neque nisi nulla"}
Post {userId = 101, id = 101, title = "test title", body = "test body"}
Post {userId = 101, id = 1, title = "test title", body = "test body"}
{}
{
  "userId": 1,
  "id": 1,
  "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
  "body": "quia et suscipit
suscipit recusandae consequuntur expedita et cum
reprehenderit molestiae ut ut quas totam
nostrum rerum est autem sunt rem eveniet architecto"
}
Post {userId = 1, id = 1, title = "sunt aut facere repellat provident occaecati excepturi optio reprehenderit", body = "quia et suscipit
suscipit recusandae consequuntur expedita et cum
reprehenderit molestiae ut ut quas totam
nostrum rerum est autem sunt rem eveniet architecto"}
Post {userId = 1, id = 1, title = "sunt aut facere repellat provident occaecati excepturi optio reprehenderit", body = "quia et suscipit
suscipit recusandae consequuntur expedita et cum
reprehenderit molestiae ut ut quas totam
nostrum rerum est autem sunt rem eveniet architecto"}
Post {userId = 1, id = 2, title = "qui est esse", body = "est rerum tempore vitae
sequi sint nihil reprehenderit dolor beatae ea dolores neque
fugiat blanditiis voluptate porro vel nihil molestiae ut reiciendis
qui aperiam non debitis possimus qui neque nisi nulla"}
Post {userId = 101, id = 1, title = "test title", body = "test body"}
Post {userId = 101, id = 101, title = "test title", body = "test body"}
{}