Json转换空字符串而不是null

问题描述 投票:25回答:4

我正在尝试序列化我的结构,以便没有获得值的字符串获取其默认值“”而不是null

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

我在Json字符串中的结果:

"myProperty": null,

我想要的是

"myProperty": "",

我也试过创建一个没有任何影响的转换器,因为某种原因,转换和WriteJson函数甚至都没有触发:

[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qazxsw poi无济于事

c# json null string
4个回答
30
投票

这应该工作:

Json.Net How to deserialize null as empty string?

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

19
投票

虽然接受的答案指出了我正确的方向,但它看起来很脆弱。我不想担心解决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); } } 对象列表并自己实现JsonProperty,因为在Json.NET中可以使用功能完善的工具(可以进行各种优化和角落案例处理,这是基本的反映 - 基于重新实现不会)。

我的解决方案执行最小的覆盖和解析器替换,以确保只有绝对需要更改的部分才会被实际更改:

IValueResolver

17
投票

好吧,我的解决方案非常简单,但不使用JSON.NET功能,只需将backend字段添加到您的属性:

public sealed class SubstituteNullWithEmptyStringContractResolver : DefaultContractResolver
{
    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
    {
        JsonProperty property = base.CreateProperty(member, memberSerialization);

        if (property.PropertyType == typeof(string))
        {
            // Wrap value provider supplied by Json.NET.
            property.ValueProvider = new NullToEmptyStringValueProvider(property.ValueProvider);
        }

        return property;
    }

    sealed class NullToEmptyStringValueProvider : IValueProvider
    {
        private readonly IValueProvider Provider;

        public NullToEmptyStringValueProvider(IValueProvider provider)
        {
            if (provider == null) throw new ArgumentNullException("provider");

            Provider = provider;
        }

        public object GetValue(object target)
        {
            return Provider.GetValue(target) ?? "";
        }

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

编辑:

在c#6.0中,属性初始化将可用:

public class Test
{
    private string _myProperty = string.Empty;

    [JsonProperty(PropertyName = "myProperty")]
    public string MyProperty
    {
        get { return _myProperty; }
        set { _myProperty = value; }
    }
}

3
投票

@Kirill Shlenskiy的解决方案很棒,但它没有考虑public class Test { [JsonProperty(PropertyName = "myProperty")] public string MyProperty { get; set;} = ""; } 属性。

NullValueHandling

这是一个改进的版本,将负责它。如果设置了[JsonProperty(NullValueHandling = NullValueHandling.Ignore)] public string Remark{ get; set; } 且值为null,则将在JSON输出中跳过它。

NullValueHandling.Ignore
© www.soinside.com 2019 - 2024. All rights reserved.