Modifying type-specific properties in implementation of interface

Question

I know this is a silly question, in that the answer is likely an "oh right, of course!" one.

Here is what I have:

public interface IEvent {
  int Id
  string Title

}

public class MeetingEvent : IEvent {
  int Id
  string Title

  //Meeting Properties
  string Room;
  User Organizer; 
}

public class BirthdayEvent : IEvent {
  int Id
  string Title

  //Bday Properties
  int Candles;
  bool Surprise;

}

I am working on a custom model binder in ASP.NET MVC as my main edit form inherits from IEvent while I perform a RenderPartial to add the other type-specific fields

When I get to the model binder, I can see all the keys/values for the type, which is good. Now, I want to do this:

IEvent _event;

switch (eventType) {  // EventType is an enum
  case EventType.Birthday:
    _event = new BirthdayEvent();

    _event.Candles= GetValue<int>(bindingContext, "Candles");
    _event.Surprise= GetValue<bool>(bindingContext, "Surprise");
    break;

  case EventType.Meeting:
    _event = new MeetingEvent();

    // Meeting-specific fields are set here...
    break;

  default:
    throw new InvalidOperationException("Invalid Event Type");
}

In essence, I want an IEvent variable and I want to create a specific event type that implements IEvent and set the type-specific fields. What Visual Studio tells me is that it can not access the BirthdayEvent fields.

While, I understand this, I can't seem to figure out what I need to do. Thus, this question :).

Thanks in advance!

Answer 1

When you first create your instances of BirthdayEvent and MeetingEvent, put them in variables of that type. That way you can assign those members. Then assign them to your _event variable. Like this:

switch (eventType) {  // EventType is an enum
  case EventType.Birthday:
  {
    var be = new BirthdayEvent();

    be.Candles= GetValue<int>(bindingContext, "Candles");
    be.Surprise= GetValue<bool>(bindingContext, "Surprise");
    _event = be;
    break;
  }
  case EventType.Meeting:
  {
    var me = new MeetingEvent();

    // Meeting-specific fields are set here...
    _event = me;
    break;
  {
  default:
    throw new InvalidOperationException("Invalid Event Type");
}

Answer 2

Something along these lines:

IEvent _event;

switch (eventType) {  // EventType is an enum
  case EventType.Birthday:
    var birthdayEvent = new BirthdayEvent();

    birthdayEvent.Candles= GetValue<int>(bindingContext, "Candles");
    birthdayEvent.Surprise= GetValue<bool>(bindingContext, "Surprise");
    _event = birthdayEvent;
    break;
  /* etc */

  default:
    throw new InvalidOperationException("Invalid Event Type");
}