重写对象ToString方法，引入Newtonsoft.Json

public override string ToString()    {      JsonSerializerSettings settings = new JsonSerializerSettings();      int num = 1;      settings.NullValueHandling = (NullValueHandling) num;      return JsonConvert.SerializeObject((object) this, Formatting.Indented, settings);    } public override string ToString()　　{　　　　return JsonConvert.SerializeObject(this);　　}