重写对象ToString方法

重写对象ToString方法，引入Newtonsoft.Json

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