当值可以是对象或空数组时，反序列化JSON

Z时代
2024-01-10
分类：问答

我正在使用VK API。有时服务器可以返回空数组而不是对象，例如：

personal: [] //when it is empty

要么

personal: {
religion: 'Нет',
smoking: 1,
alcohol: 4
} //when not empty.

我用JsonConvert.DeserializeObject反序列化大多数json，而这部分json用

MainObject = ((MainObject["response"].GetObject())["user"].GetObject())["personal"].GetObject();
try
{
Convert.ToByte(MainObject["political"].GetNumber();
} 
catch {}

但是，当它处理大量肽时，它会使应用程序运行缓慢。刚才我意识到，这里还有其他一些字段，如果为空，它们可能会返回数组。我只是不知道如何快速而清晰地做到这一点。有什么建议？

我的反序列化类（当字段为空时不起作用）：

     public class User
            {
//some other fields...
                public Personal personal { get; set; }
//some other fields...
             }
    public class Personal
            {
                public byte political { get; set; }
                public string[] langs { get; set; }
                public string religion { get; set; }
                public string inspired_by { get; set; }
                public byte people_main { get; set; }
                public byte life_main { get; set; }
                public byte smoking { get; set; }
                public byte alcohol { get; set; }
            }

另一个想法（不为空时不起作用）：

public List<Personal> personal { get; set; }

回答：

您可以JsonConverter像下面这样，查找指定类型的对象或空数组。如果是对象，它将反序列化该对象。如果为空数组，则返回null：

public class JsonSingleOrEmptyArrayConverter<T> : JsonConverter where T : class
{
    public override bool CanConvert(Type objectType)
    {
        return typeof(T).IsAssignableFrom(objectType);
    }
    public override bool CanWrite { get { return false; } }
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        var contract = serializer.ContractResolver.ResolveContract(objectType);
        if (!(contract is Newtonsoft.Json.Serialization.JsonObjectContract || contract is Newtonsoft.Json.Serialization.JsonDictionaryContract))
        {
            throw new JsonSerializationException(string.Format("Unsupported objectType {0} at {1}.", objectType, reader.Path));
        }
        switch (reader.SkipComments().TokenType)
        {
            case JsonToken.StartArray:
                {
                    int count = 0;
                    while (reader.Read())
                    {
                        switch (reader.TokenType)
                        {
                            case JsonToken.Comment:
                                break;
                            case JsonToken.EndArray:
                                return existingValue;
                            default:
                                {
                                    count++;
                                    if (count > 1)
                                        throw new JsonSerializationException(string.Format("Too many objects at path {0}.", reader.Path));
                                    existingValue = existingValue ?? contract.DefaultCreator();
                                    serializer.Populate(reader, existingValue);
                                }
                                break;
                        }
                    }
                    // Should not come here.
                    throw new JsonSerializationException(string.Format("Unclosed array at path {0}.", reader.Path));
                }
            case JsonToken.Null:
                return null;
            case JsonToken.StartObject:
                existingValue = existingValue ?? contract.DefaultCreator();
                serializer.Populate(reader, existingValue);
                return existingValue;
            default:
                throw new InvalidOperationException("Unexpected token type " + reader.TokenType.ToString());
        }
    }
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}
public static partial class JsonExtensions
{
    public static JsonReader SkipComments(this JsonReader reader)
    {
        while (reader.TokenType == JsonToken.Comment && reader.Read())
            ;
        return reader;
    }
}

然后像这样使用它：

public class User
{
    //some other fields...
    [JsonConverter(typeof(JsonSingleOrEmptyArrayConverter<Personal>))]
    public Personal personal { get; set; }
    //some other fields...
}

现在，您应该可以将用户反序列化到您的User班级中。

笔记：