Question

我无法在客户端端点反序列化JSON数据。它接收如下的JSON数据：

{
    "WaitForClientMessagesResult": [
        {
            "__type": "KeepAliveMessage:#Data.WebGateway",
            "MessageId": 1,
            "Type": 0,
            "PositionInQueue": -1
        }
    ]
}

KeepAliveMessage是WebResponseMessage的派生类。该服务返回IEnumerable<WebResponseMessage>。

我得到这样的例外：

Newtonsoft.Json.JsonSerializationException：

无法将当前JSON对象（例如{“name”：“value”}）反序列化为类型   “System.Collections.Generic.IEnumerable`1 [   Red5Prototype.Models.WaitForClientMessagesResult]

因为类型需要JSON数组（例如[1,2,3]）才能正确反序列化。

我尝试过很多方式调用反序列化：

WaitForClientMessagesResult deserialized = JsonConvert.DeserializeObject<WaitForClientMessagesResult>(keepAliveResult);
WaitForClientMessagesResult[] deserialized = JsonConvert.DeserializeObject<WaitForClientMessagesResult[]>(keepAliveResult);
IEnumerable<WebClientMessage> deserialized = JsonConvert.DeserializeObject<IEnumerable<WebClientMessage>>(keepAliveResult);

如果这些工作没有。

我不确定如何在客户端构造我的类以使用Json反序列化器。

修改我的基类定义如下：

[KnownType(typeof(KeepAliveMessage))]    
[DataContract]
public abstract class WebClientMessage
{
    public WebClientMessage() { }

    [DataMember]
    public int MessageId { get; set; }
    [DataMember]
    public WebClientMessageType Type { get; set; }
}

与Keepalive一样：

[DataContract]
public class KeepAliveMessage : WebClientMessage
{
    public KeepAliveMessage() { }

    [DataMember]
    public int PositionInQueue { get; set; }
}

我尝试让WebClientMessage成为WaitForClientMessagesResult

的成员

[DataContract]
public class WaitForClientMessagesResult
{
    public WaitForClientMessagesResult() {}

    [DataMember]
    WebClientMessage [] Messages;
}

这也不起作用。

Answer 1

There are two issues here. Firstly, the JSON root object has an array-valued property named WaitForClientMessagesResult not Messages so you need to do something like this:

[DataContract(Name = "WaitForClientMessagesResult", Namespace = "http://schemas.datacontract.org/2004/07/Data.WebGateway")]
public class WaitForClientMessagesResult
{
    public WaitForClientMessagesResult() { }

    [DataMember(Name = "WaitForClientMessagesResult")]
    public WebClientMessage[] Messages { get; set; }
}

Secondly, your JSON contains polymorphic type hints in the DataContractJsonSerializer format. The JSON serializer you are using, Json.NET, does not support this format. Therefore, you might consider switching to DataContractJsonSerializer. Using it I was able to deserialize your JSON as follows:

public enum WebClientMessageType
{
    KeepAliveMessage,
}

[KnownType(typeof(KeepAliveMessage))]
[DataContract(Name="WebClientMessage", Namespace="http://schemas.datacontract.org/2004/07/Data.WebGateway")]
public abstract class WebClientMessage
{
    public WebClientMessage() { }

    [DataMember]
    public int MessageId { get; set; }

    [DataMember]
    public WebClientMessageType Type { get; set; }
}

[DataContract(Name = "KeepAliveMessage", Namespace = "http://schemas.datacontract.org/2004/07/Data.WebGateway")]
public class KeepAliveMessage : WebClientMessage
{
    public KeepAliveMessage() { }

    [DataMember]
    public int PositionInQueue { get; set; }
}

public static class DataContractJsonSerializerHelper
{
    public static string GetJson<T>(T obj, DataContractJsonSerializer serializer)
    {
        using (var memory = new MemoryStream())
        {
            serializer.WriteObject(memory, obj);
            memory.Seek(0, SeekOrigin.Begin);
            using (var reader = new StreamReader(memory))
            {
                return reader.ReadToEnd();
            }
        }
    }

    public static string GetJson<T>(T obj)
    {
        var serializer = new DataContractJsonSerializer(typeof(T));
        return GetJson(obj, serializer);
    }

    public static T GetObject<T>(string json, DataContractJsonSerializer serializer)
    {
        using (var stream = GenerateStreamFromString(json))
        {
            var obj = serializer.ReadObject(stream);
            return (T)obj;
        }
    }

    public static T GetObject<T>(string json)
    {
        var serializer = new DataContractJsonSerializer(typeof(T));
        return GetObject<T>(json, serializer);
    }

    private static MemoryStream GenerateStreamFromString(string value)
    {
        return new MemoryStream(Encoding.Unicode.GetBytes(value ?? ""));
    }
}

And then, to test:

    public static void Test()
    {
        // Note there cannot be a space between the "{" and the "_type": 
        string json = @"{
            ""WaitForClientMessagesResult"": [
                {""__type"": ""KeepAliveMessage:#Data.WebGateway"",
                    ""MessageId"": 1,
                    ""Type"": 0,
                    ""PositionInQueue"": -1
                }
            ]
        }";
        var result = DataContractJsonSerializerHelper.GetObject<WaitForClientMessagesResult>(json);
        var newJson = DataContractJsonSerializerHelper.GetJson(result);

        Debug.Assert(JToken.DeepEquals(JToken.Parse(json), JToken.Parse(newJson))); // No assert
    }

If you want to stick with Json.NET you will need to write your own JsonConverter that parses the "__type" property and deserializes the correct concrete type.

Answer 2

这是我最终解决这个问题的方法。它有点破解，但现在必须要做：

    Dictionary<string, object> deserialized = JsonConvert.DeserializeObject<Dictionary<string, object>>(json);
    JArray messagesArray = deserialized["WaitForClientMessagesResult"] as JArray;

    foreach (JObject gatewayMessage in messagesArray.Children<JObject>())
    {
        string messageJson = gatewayMessage.ToString();
        WebClientMessageType messageType = GetMessageType(gatewayMessage);
        WaitForClientMessagesResult msg = null;

        switch (messageType)
        {
            case WebClientMessageType.KeepAlive:
                msg = JsonConvert.DeserializeObject<KeepAliveMessage>(messageJson);
                break;
            default:
                break;
        }

    }

我已经剥离了其他业务逻辑，刚刚发布了Json处理。如果有更好的方法，我会稍后探讨。

Thnx为大家提供帮助:)没有您的反馈，我无法到达这里

马特

客户端上的Json反序列化类结构

2 个答案: