Json 转换空字符串而不是 null

问题描述

我正在尝试序列化我的结构，以便没有获得值的字符串获得它们的默认值 "" 而不是 null

I'm trying to serialize my struct so that the strings that didn't get a value get their default value "" instead of null

[JsonProperty(PropertyName = "myProperty", DefaultValueHandling = DefaultValueHandling.Populate)]
[DefaultValue("")]
public string MyProperty{ get; set; }

我在 Json 字符串中的结果:

My result in the Json string:

"myProperty": null,

我想要什么

"myProperty": "",

我也尝试创建一个没有任何效果的转换器，can Convert 和 WriteJson 函数由于某种原因甚至没有触发:

I also tried creating a converter without any effect, the can Convert and WriteJson functions aren't even firing for some reason:

[JsonProperty(PropertyName = "myProperty")]
[JsonConverter(typeof(NullToEmptyStringConverter))]
public string MyProperty{ get; set; }

class NullToEmptyStringConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(object[]);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        if (value == null)
            writer.WriteValue("");
    }
}

这对 Json.Net 如何反序列化 null 没有帮助作为空字符串?

推荐答案

这应该有效:

var settings = new JsonSerializerSettings() { ContractResolver= new NullToEmptyStringResolver() };
var str = JsonConvert.SerializeObject(yourObj, settings);

<小时>

public class NullToEmptyStringResolver : Newtonsoft.Json.Serialization.DefaultContractResolver
{
    protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
    {
        return type.GetProperties()
                .Select(p=>{
                    var jp = base.CreateProperty(p, memberSerialization);
                    jp.ValueProvider = new NullToEmptyStringValueProvider(p);
                    return jp;
                }).ToList();
    }
}

public class NullToEmptyStringValueProvider : IValueProvider
{
    PropertyInfo _MemberInfo;
    public NullToEmptyStringValueProvider(PropertyInfo memberInfo)
    {
        _MemberInfo = memberInfo;
    }

    public object GetValue(object target)
    {
        object result =  _MemberInfo.GetValue(target);
        if (_MemberInfo.PropertyType == typeof(string) && result == null) result = "";
        return result;

    }

    public void SetValue(object target, object value)
    {
        _MemberInfo.SetValue(target, value);
    }
}