小编典典

使用json.net反序列化没有类型信息的多态json类

c#

Imgur api调用返回一个列表,其中包含以JSON表示的
Gallery ImageGallery Album 类。

鉴于没有$ type属性告诉反序列化器要表示哪个类,因此我看不到如何使用Json.NET自动反序列化。有一个称为“ IsAlbum”的属性,可用于区分两者。

这个问题似乎显示出一种方法,但看起来有点像个hack。

我该如何反序列化这些类? (使用C#,Json.NET)

样本数据:

图库图片

{
    "id": "OUHDm",
    "title": "My most recent drawing. Spent over 100 hours.",
        ...
    "is_album": false
}

画廊专辑

{
    "id": "lDRB2",
    "title": "Imgur Office",
    ...
    "is_album": true,
    "images_count": 3,
    "images": [
        {
            "id": "24nLu",
            ...
            "link": "http://i.imgur.com/24nLu.jpg"
        },
        {
            "id": "Ziz25",
            ...
            "link": "http://i.imgur.com/Ziz25.jpg"
        },
        {
            "id": "9tzW6",
            ...
            "link": "http://i.imgur.com/9tzW6.jpg"
        }
    ]
}
}

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2020-05-19

共1个答案

小编典典

通过创建JsonConverter用于处理对象实例化的自定义,您可以相当轻松地做到这一点。假设您的类定义如下:

public abstract class GalleryItem
{
    public string id { get; set; }
    public string title { get; set; }
    public string link { get; set; }
    public bool is_album { get; set; }
}

public class GalleryImage : GalleryItem
{
    // ...
}

public class GalleryAlbum : GalleryItem
{
    public int images_count { get; set; }
    public List<GalleryImage> images { get; set; }
}

您将这样创建转换器:

public class GalleryItemConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return typeof(GalleryItem).IsAssignableFrom(objectType);
    }

    public override object ReadJson(JsonReader reader, 
        Type objectType, object existingValue, JsonSerializer serializer)
    {
        JObject jo = JObject.Load(reader);

        // Using a nullable bool here in case "is_album" is not present on an item
        bool? isAlbum = (bool?)jo["is_album"];

        GalleryItem item;
        if (isAlbum.GetValueOrDefault())
        {
            item = new GalleryAlbum();
        }
        else
        {
            item = new GalleryImage();
        }

        serializer.Populate(jo.CreateReader(), item);

        return item;
    }

    public override bool CanWrite
    {
        get { return false; }
    }

    public override void WriteJson(JsonWriter writer, 
        object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

这是一个示例程序,显示了运行中的转换器:

class Program
{
    static void Main(string[] args)
    {
        string json = @"
        [
            {
                ""id"": ""OUHDm"",
                ""title"": ""My most recent drawing. Spent over 100 hours."",
                ""link"": ""http://i.imgur.com/OUHDm.jpg"",
                ""is_album"": false
            },
            {
                ""id"": ""lDRB2"",
                ""title"": ""Imgur Office"",
                ""link"": ""http://alanbox.imgur.com/a/lDRB2"",
                ""is_album"": true,
                ""images_count"": 3,
                ""images"": [
                    {
                        ""id"": ""24nLu"",
                        ""link"": ""http://i.imgur.com/24nLu.jpg""
                    },
                    {
                        ""id"": ""Ziz25"",
                        ""link"": ""http://i.imgur.com/Ziz25.jpg""
                    },
                    {
                        ""id"": ""9tzW6"",
                        ""link"": ""http://i.imgur.com/9tzW6.jpg""
                    }
                ]
            }
        ]";

        List<GalleryItem> items = 
            JsonConvert.DeserializeObject<List<GalleryItem>>(json, 
                new GalleryItemConverter());

        foreach (GalleryItem item in items)
        {
            Console.WriteLine("id: " + item.id);
            Console.WriteLine("title: " + item.title);
            Console.WriteLine("link: " + item.link);
            if (item.is_album)
            {
                GalleryAlbum album = (GalleryAlbum)item;
                Console.WriteLine("album images (" + album.images_count + "):");
                foreach (GalleryImage image in album.images)
                {
                    Console.WriteLine("    id: " + image.id);
                    Console.WriteLine("    link: " + image.link);
                }
            }
            Console.WriteLine();
        }
    }
}

这是上面程序的输出:

id: OUHDm
title: My most recent drawing. Spent over 100 hours.
link: http://i.imgur.com/OUHDm.jpg

id: lDRB2
title: Imgur Office
link: http://alanbox.imgur.com/a/lDRB2
album images (3):
    id: 24nLu
    link: http://i.imgur.com/24nLu.jpg
    id: Ziz25
    link: http://i.imgur.com/Ziz25.jpg
    id: 9tzW6
    link: http://i.imgur.com/9tzW6.jpg

小提琴:https :
//dotnetfiddle.net/1kplME

2020-05-19