正如James Newton King所述:如果你自己创建序列化器，而不是使用JavaScriptConvert，那么你可以将NullValueHandling属性设置为忽略。

下面是一个例子:

JsonSerializer _jsonWriter = new JsonSerializer {
                                 NullValueHandling = NullValueHandling.Ignore
                             };

或者，按照@amit的建议

JsonConvert.SerializeObject(myObject, 
                            Newtonsoft.Json.Formatting.None, 
                            new JsonSerializerSettings { 
                                NullValueHandling = NullValueHandling.Ignore
                            });

可以在他们的网站(http://james.newtonking.com/archive/2009/10/23/efficient-json-with-json-net-reducing-serialized-json-size.aspx)上的这个链接中看到，我支持使用[Default()]来指定默认值

摘自链接

   public class Invoice
{
  public string Company { get; set; }
  public decimal Amount { get; set; }

  // false is default value of bool
  public bool Paid { get; set; }
  // null is default value of nullable
  public DateTime? PaidDate { get; set; }

  // customize default values
  [DefaultValue(30)]
  public int FollowUpDays { get; set; }
  [DefaultValue("")]
  public string FollowUpEmailAddress { get; set; }
}


Invoice invoice = new Invoice
{
  Company = "Acme Ltd.",
  Amount = 50.0m,
  Paid = false,
  FollowUpDays = 30,
  FollowUpEmailAddress = string.Empty,
  PaidDate = null
};

string included = JsonConvert.SerializeObject(invoice,
  Formatting.Indented,
  new JsonSerializerSettings { });

// {
//   "Company": "Acme Ltd.",
//   "Amount": 50.0,
//   "Paid": false,
//   "PaidDate": null,
//   "FollowUpDays": 30,
//   "FollowUpEmailAddress": ""
// }

string ignored = JsonConvert.SerializeObject(invoice,
  Formatting.Indented,
  new JsonSerializerSettings { DefaultValueHandling = DefaultValueHandling.Ignore });

// {
//   "Company": "Acme Ltd.",
//   "Amount": 50.0
// }

你可以写:[JsonProperty("property_name"，DefaultValueHandling = DefaultValueHandling. ignore)]

它还负责使用默认值(不仅仅是null)不序列化属性。例如，它对枚举很有用。

对于System.Text.Json和.NET Core 3.0，这对我来说是可行的:

var jsonSerializerOptions = new JsonSerializerOptions()
{
    IgnoreNullValues = true
};
var myJson = JsonSerializer.Serialize(myObject, jsonSerializerOptions );

这里有一个类似的选项，但提供了另一种选择:

public class DefaultJsonSerializer : JsonSerializerSettings
{
    public DefaultJsonSerializer()
    {
        NullValueHandling = NullValueHandling.Ignore;
    }
}

然后，我这样使用它:

JsonConvert.SerializeObject(postObj, new DefaultJsonSerializer());

不同之处在于:

Reduces repeated code by instantiating and configuring JsonSerializerSettings each place it's used. Saves time in configuring every property of every object to be serialized. Still gives other developers flexibility in serialization options, rather than having the property explicitly specified on a reusable object. My use-case is that the code is a 3rd party library and I don't want to force serialization options on developers who would want to reuse my classes. Potential drawbacks are that it's another object that other developers would need to know about, or if your application is small and this approach wouldn't matter for a single serialization.

使用JsonProperty属性的替代解决方案:

[JsonProperty(NullValueHandling=NullValueHandling.Ignore)]
// or
[JsonProperty("property_name", NullValueHandling=NullValueHandling.Ignore)]

// or for all properties in a class
[JsonObject(ItemNullValueHandling = NullValueHandling.Ignore)]

在这个在线文档中可以看到。