c# - 如何使用 JSON.NET 将带有空值的 json 数组反序列化为不可空的 int 列表？

Question

我有以下 json 部分给我带来了麻烦:

"edges":["5","","5",""]}

我正在尝试反序列化为以下属性:

public class Redacted
{
    ...

    [JsonProperty("edges", NullValueHandling = NullValueHandling.Ignore)]
    public List<int> Edges { get; set; } = new();

    ...
}

然而，这给了我以下错误:

Newtonsoft.Json.JsonSerializationException
  HResult=0x80131500
  Message=Error converting value {null} to type 'System.Int32'. Path 'edges[1]', line 1, position 186.
  Source=Newtonsoft.Json
  StackTrace:
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.EnsureType(JsonReader reader, Object value, CultureInfo culture, JsonContract contract, Type targetType)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateList(IList list, JsonReader reader, JsonArrayContract contract, JsonProperty containerProperty, String id)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateList(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, Object existingValue, String id)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.SetPropertyValue(JsonProperty property, JsonConverter propertyConverter, JsonContainerContract containerContract, JsonProperty containerProperty, JsonReader reader, Object target)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateObject(Object newObject, JsonReader reader, JsonObjectContract contract, JsonProperty member, String id)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Populate(JsonReader reader, Object target)
   at REDACTED.ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer) in REDACTED.cs:line 45

  This exception was originally thrown at this call stack:
    System.Convert.ChangeType(object, System.Type, System.IFormatProvider)
    Newtonsoft.Json.Serialization.JsonSerializerInternalReader.EnsureType(Newtonsoft.Json.JsonReader, object, System.Globalization.CultureInfo, Newtonsoft.Json.Serialization.JsonContract, System.Type)

Inner Exception 1:
InvalidCastException: Null object cannot be converted to a value type.

我试图指定 NullValueHandling.Ignore在我的模型中，但这似乎只适用于属性，而不适用于列表中的项目。

我宁愿不必设置 NullValueHandling.Ignore在设置中，它应该只适用于这个特定的属性。

如何将此 json 反序列化为 List<int> ？

Answer 1

由于您使用的是 Json.NET，因此您可以构建一个自定义转换器来处理空的 string 并将它们转换为 int。这是一个开始:

public class NullableStringToIntConverter : JsonConverter
{
    public override bool CanConvert(Type objectType) => typeof(List<string>) == objectType;

    public override object ReadJson(JsonReader reader, Type objectType,
        object existingValue, JsonSerializer serializer)
    {
        var items = serializer.Deserialize<List<string>>(reader);
        
        return items
            .Where(s => !string.IsNullOrEmpty(s))
            .Select(int.Parse)
            .ToList();
            
        throw new NotImplementedException();
    }

    public override void WriteJson(JsonWriter writer, object value, 
        JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

你要反序列化的类看起来像这样:

public class Thing
{
    [JsonConverter(typeof(NullableStringToIntConverter))]
    public List<int> Edges { get; set; }
}

最后反序列化:

var thing = JsonConvert.DeserializeObject<Thing>(json);