Question

If I have two windows in an oob application how do I communicate between them?

This is the new feature of silverlight 5 that allows for multiple windows.

Answer 1

They run in a common application. Hence they share the same static data. The scope of communication choices are therefore very large. Here is an example:-

public class MessageEventArgs : EventArgs
{
      public MessageEventArgs(object payload)
      {
           Payload = payload;
      }

      public object Payload {get; private set; }
}

public class Messenger
{
    private static readonly Messenger _current = new Messenger();
    public static Messenger Current { get { return _current; } }

    public event EventHandler<MessageEventArgs> MessageReceived;

    public void Send(object payload)
    {
          if (MessageReceived != null)
               MessageReceived(this, new MessageEventArgs(payload));
    }
}

All windows can attach a handler to Messenger.Current.MessageReceived (just be sure to detach when the window closes) and any window can call Messenger.Current.Send.

Ok so you wouldn’t actually use this code its a bit rubbish, the point is Windows in SL5 are not isolated. You can create whatever internal application communication mechanism you need.