设置 NullValueHandling = NullValueHandling.Ignore 不会在反序列化期间自动过滤 JSON 数组中的空值，因为这样做会导致数组中的剩余项被重新索引，从而使可能具有的任何数组索引无效存储在序列化图中的其他位置。
如果您不关心保留数组索引并希望在反序列化期间从数组中过滤空值，则需要实现custom JsonConverter，如下所示：
public class NullFilteringListConverter<T> : JsonConverter<List<T>>
{
public override List<T> ReadJson(JsonReader reader, Type objectType, List<T> existingValue, bool hasExistingValue, JsonSerializer serializer)
{
if (reader.MoveToContentAndAssert().TokenType == JsonToken.Null)
return null;
var list = existingValue as List<T> ?? (List<T>)serializer.ContractResolver.ResolveContract(objectType).DefaultCreator();
serializer.Populate(reader, list);
list.RemoveAll(i => i == null);
return list;
}
public override bool CanWrite => false;
public override void WriteJson(JsonWriter writer, List<T> value, JsonSerializer serializer) => throw new NotImplementedException();
}
public static partial class JsonExtensions
{
public static JsonReader MoveToContentAndAssert(this JsonReader reader)
{
if (reader == null)
throw new ArgumentNullException();
if (reader.TokenType == JsonToken.None) // Skip past beginning of stream.
reader.ReadAndAssert();
while (reader.TokenType == JsonToken.Comment) // Skip past comments.
reader.ReadAndAssert();
return reader;
}
public static JsonReader ReadAndAssert(this JsonReader reader)
{
if (reader == null)
throw new ArgumentNullException();
if (!reader.Read())
throw new JsonReaderException("Unexpected end of JSON stream.");
return reader;
}
}
并将其应用于您的模型，如下所示：
public class Class1
{
public string Variable1 { get; set; }
public string Variable2 { get; set; }
[JsonConverter(typeof(NullFilteringListConverter<ArrayObject>))]
public List<ArrayObject> ArrayObject { get; set; }
}
或者，在设置中添加如下：
var settings = new JsonSerializerSettings()
{
ReferenceLoopHandling = ReferenceLoopHandling.Ignore,
NullValueHandling = NullValueHandling.Ignore,
Converters = { new NullFilteringListConverter<ArrayObject>() },
};
注意事项：
-
由于您在序列化期间没有询问过滤空值，因此我没有实现它，但是通过更改 CanWrite => true; 并将 WriteJson() 替换为：
public override void WriteJson(JsonWriter writer, List<T> value, JsonSerializer serializer) => serializer.Serialize(writer, value.Where(i => i != null));
演示小提琴here 和here。
更新
我需要一个全局解决方案。 如果您需要从每个模型中所有可能的 List<T> 对象中自动过滤所有 null 值，那么以下 JsonConverter 将完成这项工作： p>
public class NullFilteringListConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
if (objectType.IsArray || objectType == typeof(string) || objectType.IsPrimitive)
return false;
var itemType = objectType.GetListItemType();
return itemType != null && (!itemType.IsValueType || Nullable.GetUnderlyingType(itemType) != null);
}
object ReadJsonGeneric<T>(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
var list = existingValue as List<T> ?? (List<T>)serializer.ContractResolver.ResolveContract(objectType).DefaultCreator();
serializer.Populate(reader, list);
list.RemoveAll(i => i == null);
return list;
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
if (reader.MoveToContentAndAssert().TokenType == JsonToken.Null)
return null;
var itemType = objectType.GetListItemType();
var method = typeof(NullFilteringListConverter).GetMethod("ReadJsonGeneric", BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public);
try
{
return method.MakeGenericMethod(new[] { itemType }).Invoke(this, new object[] { reader, objectType, existingValue, serializer });
}
catch (Exception ex)
{
// Wrap the TargetInvocationException in a JsonSerializerException
throw new JsonSerializationException("Failed to deserialize " + objectType, ex);
}
}
public override bool CanWrite => false;
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer) => throw new NotImplementedException();
}
public static partial class JsonExtensions
{
internal static Type GetListItemType(this Type type)
{
// Quick reject for performance
if (type.IsPrimitive || type.IsArray || type == typeof(string))
return null;
while (type != null)
{
if (type.IsGenericType)
{
var genType = type.GetGenericTypeDefinition();
if (genType == typeof(List<>))
return type.GetGenericArguments()[0];
}
type = type.BaseType;
}
return null;
}
}
并将其添加到设置中，如下所示：
var settings = new JsonSerializerSettings()
{
ReferenceLoopHandling = ReferenceLoopHandling.Ignore,
NullValueHandling = NullValueHandling.Ignore,
Converters = { new NullFilteringListConverter() },
};
Class1 class1 = JsonConvert.DeserializeObject<Class1>(json, settings);
使用此转换器，不再需要将[JsonConverter(typeof(NullFilteringListConverter<ArrayObject>))] 添加到ArrayObject。请注意，反序列化图中的所有 List<T> 实例可能会在使用这些设置时重新索引！确保您确实希望这是更改其他地方引用的项目索引的副作用索引可能包括数据损坏（不正确的引用）而不是直接的ArgumentOutOfRangeException。
演示小提琴#3 here.