客户端上的Json反序列化类结构

Question

我无法在客户端端点上反序列化JSON数据。 它接收这样的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> 。

我收到这样的异常：

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]

因为该类型需要JSON数组（例如[1,2,3]）才能正确反序列化。

我尝试过多种方式调用反序列化：

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

如果这些有效，则无。

我不确定如何在客户端上构造类以使用Json反序列化器。

编辑：我的基类是这样定义的：

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

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

与Keepalive像这样：

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

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

我试图使WebClientMessage成为WaitForClientMessagesResult的成员

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

    [DataMember]
    WebClientMessage [] Messages;
}

那也不起作用。

Answer 1

这里有两个问题。 首先，JSON根对象具有一个名为WaitForClientMessagesResult而不是Messages的数组值属性，因此您需要执行以下操作：

[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; }
}

其次，您的JSON包含DataContractJsonSerializer格式的多态类型提示 。 您使用的JSON序列化程序Json.NET 不支持此格式 。 因此，您可以考虑切换到DataContractJsonSerializer 。 使用它，我可以如下反序列化您的JSON：

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 ?? ""));
    }
}

然后，进行测试：

    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
    }

如果您想使用Json.NET，则需要编写自己的JsonConverter来解析"__type"属性并反序列化正确的具体类型。

Answer 2

这就是我最终解决此问题的方式。 这有点hack，但是现在必须这样做：

    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;
        }

    }

我删除了其他业务逻辑，并发布了Json处理信息。 如果有更好的方法，我将在以后进行探讨。

谢谢大家的帮助：)没有您的反馈，我无法到达这里

马特