test.cs

public class SmartFormField {
  public string Name { get; set; }
  public string Text { get; set; }
  public string DisplayName { get; set; }
}

public class SmartTextFormField : SmartFormField {
  public string TypeName { get; set; } = "SmartTextFormField";
}

public class SmartCheckboxField : SmartFormField {
  public bool Checked { get; set; }
  public string TypeName { get; set; } = "SmartCheckboxField";
}

public class SmartDropdownField : SmartFormField {
  public List<string> Items { get; set; } = new List<string>();
  public string TypeName { get; set; } = "SmartDropdownField";
}

public class SmartDateField : SmartFormField {
  public string Date { get; set; }
  public string TypeName { get; set; } = "SmartDateField";
}