問題描述

我在使用 JSON.NET 庫反序列化從 Facebook 返回的數據時遇到了一些麻煩.

I'm having a bit of trouble deserializing data returned from Facebook using the JSON.NET libraries.

從一個簡單的墻貼返回的 JSON 如下所示:

The JSON returned from just a simple wall post looks like:

{
    "attachment":{"description":""},
    "permalink":"http://www.facebook.com/permalink.php?story_fbid=123456789"
}

為照片返回的 JSON 如下所示:

The JSON returned for a photo looks like:

"attachment":{
        "media":[
            {
                "href":"http://www.facebook.com/photo.php?fbid=12345",
                "alt":"",
                "type":"photo",
                "src":"http://photos-b.ak.fbcdn.net/hphotos-ak-ash1/12345_s.jpg",
                "photo":{"aid":"1234","pid":"1234","fbid":"1234","owner":"1234","index":"12","width":"720","height":"482"}}
        ],

一切都很好，我沒有問題.我現在遇到了一個來自移動客戶端的簡單墻貼，其中包含以下 JSON，而反序列化現在因這一個帖子而失敗:

Everything works great and I have no problems. I've now come across a simple wall post from a mobile client with the following JSON, and deserialization now fails with this one single post:

"attachment":
    {
        "media":{},
        "name":"",
        "caption":"",
        "description":"",
        "properties":{},
        "icon":"http://www.facebook.com/images/icons/mobile_app.gif",
        "fb_object_type":""
    },
"permalink":"http://www.facebook.com/1234"

這是我反序列化的類:

public class FacebookAttachment
    {
        public string Name { get; set; }
        public string Description { get; set; }
        public string Href { get; set; }
        public FacebookPostType Fb_Object_Type { get; set; }
        public string Fb_Object_Id { get; set; }

        [JsonConverter(typeof(FacebookMediaJsonConverter))]
        public List<FacebookMedia> { get; set; }

        public string Permalink { get; set; }
    }

如果不使用 FacebookMediaJsonConverter，我會收到錯誤消息:無法將 JSON 對象反序列化為類型System.Collections.Generic.List`1[FacebookMedia]".這是有道理的，因為在 JSON 中，Media 不是一個集合.

Without using the FacebookMediaJsonConverter, I get an error: Cannot deserialize JSON object into type 'System.Collections.Generic.List`1[FacebookMedia]'. which makes sense, since in the JSON, Media is not a collection.

我發現這篇文章描述了一個類似的問題，所以我試圖走這條路:反序列化JSON，有時value是一個數組，有時是"(空字符串)

I found this post which describes a similar problem, so I've attempted to go down this route: Deserialize JSON, sometimes value is an array, sometimes "" (blank string)

我的轉換器看起來像:

public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
     if (reader.TokenType == JsonToken.StartArray)
          return serializer.Deserialize<List<FacebookMedia>>(reader);
     else
          return null;
}

效果很好，只是我現在遇到了一個新異常:

Which works fine, except I now get a new exception:

在 JsonSerializerInternalReader.cs 內部，CreateValueInternal():反序列化對象時出現意外令牌:PropertyName

Inside JsonSerializerInternalReader.cs, CreateValueInternal(): Unexpected token while deserializing object: PropertyName

reader.Value 的值是永久鏈接".我可以在 switch 中清楚地看到 JsonToken.PropertyName 沒有案例.

The value of reader.Value is "permalink". I can clearly see in the switch that there's no case for JsonToken.PropertyName.

我需要在轉換器中做一些不同的事情嗎?謝謝你的幫助.

Is there something I need to do differently in my converter? Thanks for any help.

推薦答案

JSON.NET 的開發人員最終幫助了項目 codeplex 網站.這是解決方案:

The developer of JSON.NET ended up helping on the projects codeplex site. Here is the solution:

問題是，當它是一個 JSON 對象時，我沒有讀取過去的屬性.這是正確的代碼:

The problem was, when it was a JSON object, I wasn't reading past the attribute. Here is the correct code:

public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
    if (reader.TokenType == JsonToken.StartArray)
    {
        return serializer.Deserialize<List<FacebookMedia>>(reader);
    }
    else
    {
        FacebookMedia media = serializer.Deserialize<FacebookMedia>(reader);
        return new List<FacebookMedia>(new[] {media});
    }
}

James 也很友好地為上述方法提供了單元測試.

James was also kind enough to provide unit tests for the above method.

這篇關于有時是數組有時是對象時反序列化JSON的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！