使用 json.net 反序列化没有类型信息的多态 json 类 [英] Deserializing polymorphic json classes without type information using json.net
问题描述
这个 Imgur api 调用返回一个包含两个画廊图像的列表和以 JSON 表示的画廊相册类.
This Imgur api call returns a list containing both Gallery Image and Gallery Album classes represented in JSON.
我看不出如何使用 Json.NET 自动反序列化这些,因为没有 $type 属性告诉反序列化器要表示哪个类.有一个名为IsAlbum"的属性可用于区分两者.
I can't see how to deserialize these automatically using Json.NET given that there is no $type property telling the deserializer which class is meant to be represented. There is a property called "IsAlbum" that can be used to differentiate between the two.
这个问题似乎表明一种方法,但看起来有点像黑客.
This question appears to show one method but it looks like a bit of a 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
}
相册
{
"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"
}
]
}
}
推荐答案
通过创建自定义 JsonConverter
来处理对象实例化,您可以相当轻松地做到这一点.假设您的类定义如下:
You can do this fairly easily by creating a custom JsonConverter
to handle the object instantiation. Assuming you have your classes defined something like this:
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; }
}
您可以像这样创建转换器:
You would create the converter like this:
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();
}
}
以下是显示转换器运行的示例程序:
Here's an example program showing the converter in action:
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
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