Newtonsoft JSON.NET解析为自定义键/值对对象的数组

  • Z时代
  • 2024-01-10
  • 分类：问答

我在解析给定的JSON数据时遇到了一个奇怪的问题。我有这个JSON结构：

{"value":[
  {"street":"Karlova 25"},
  {"city":"Prague"},
  {"gpsLat":"50.1571"},
  {"gpsLon":"15.0482"}
]}

如何使用Newtonsoft JSON.NET库解析此结构？我尝试使用自己的JsonConverter类：

public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer){
  JArray jarray = (JArray)((JTokenReader)reader).CurrentToken;
  List<AddressValue> values = new List<AddressValue>();
  foreach (var jobj in jarray.Children<JObject>()){
    foreach (JProperty prop in jobj.Properties()){
      values.Add(new AddressValue() { Label = prop.Name, Value = prop.Value.ToString() });
    }
  }
  return values.ToArray();
}
class AddressValue{
  public string Label { get; set; }
  public string Value { get; set; }
}

但我有一个例外：

Exception thrown: 'Newtonsoft.Json.JsonSerializationException' in Newtonsoft.Json.DLL
Additional information: Unexpected token when deserializing object: StartObject. Path 'value[0]'.

编辑：我也试图将其保存到字典：

 [JsonProperty(PropertyName = "value")]
 public Dictionary<string, string> Value{get; set;}

但我还有一个例外：

$exception  {"Cannot deserialize the current JSON array (e.g. [1,2,3]) into type 'System.Collections.Generic.Dictionary`2[System.String,System.String]' because the type requires a JSON object (e.g. {\"name\":\"value\"}) to deserialize correctly.\r\nTo fix this error either change the JSON to a JSON object (e.g. {\"name\":\"value\"}) or change the deserialized type to an array or a type that implements a collection interface (e.g. ICollection, IList) like List<T> that can be deserialized from a JSON array. JsonArrayAttribute can also be added to the type to force it to deserialize from a JSON array.\r\nPath 'param.value'."}

我做错了什么？谢谢您的回答。

回答：

您似乎想要Dictionary<string,

string>在JSON中将a表示为对象数组，其中每个嵌套对象都有一个来自字典的键和值。您可以使用以下转换器进行操作：

public class DictionaryToDictionaryListConverter<TKey, TValue> : JsonConverter 
{
    class DictionaryDTO : Dictionary<TKey, TValue>
    {
        public DictionaryDTO(KeyValuePair<TKey, TValue> pair) : base(1) { Add(pair.Key, pair.Value); }
    }
    public override bool CanConvert(Type objectType)
    {
        return typeof(IDictionary<TKey, TValue>).IsAssignableFrom(objectType) && objectType != typeof(DictionaryDTO);
    }
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (reader.TokenType == JsonToken.Null)
            return null;
        var token = JToken.Load(reader);
        var dict = (IDictionary<TKey, TValue>)(existingValue as IDictionary<TKey, TValue> ?? serializer.ContractResolver.ResolveContract(objectType).DefaultCreator());
        if (token.Type == JTokenType.Array)
        {
            foreach (var item in token)
                using (var subReader = item.CreateReader())
                    serializer.Populate(subReader, dict);
        }
        else if (token.Type == JTokenType.Object)
        {
            using (var subReader = token.CreateReader())
                serializer.Populate(subReader, dict);
        }
        return dict;
    }
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var dict = (IDictionary<TKey, TValue>)value;
        // Prevent infinite recursion of converters by using DictionaryDTO
        serializer.Serialize(writer, dict.Select(p => new DictionaryDTO(p)));
    }
}

然后在容器类中使用它，如下所示：

public class RootObject
{
    [JsonProperty("value")]
    [JsonConverter(typeof(DictionaryToDictionaryListConverter<string, string>))]
    public Dictionary<string, string> Value { get; set; }
}

请注意，如果键不是唯一的，转换器将在读取过程中引发异常。

对于AddressValue您可以使用下面的转换器：

public class AddressValueConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(AddressValue);
    }
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (reader.TokenType == JsonToken.Null)
            return null;
        var addressValue = (existingValue as AddressValue ?? new AddressValue());
        var token = JObject.Load(reader);
        var property = token.Properties().SingleOrDefault();
        if (property != null)
        {
            addressValue.Label = property.Name;
            addressValue.Value = (string)property.Value;
        }
        return addressValue;
    }
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var addressValue = (AddressValue)value;
        serializer.Serialize(writer, new Dictionary<string, string> { { addressValue.Label, addressValue.Value } });
    }
}

然后按以下方式使用它：

[JsonConverter(typeof(AddressValueConverter))]
public class AddressValue
{
    public string Label { get; set; }
    public string Value { get; set; }
}
public class RootObject
{
    [JsonProperty("value")]
    public List<AddressValue> Value { get; set; }
}

演示在这里摆弄了这两种选择。

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