title: Translate CancelableEvent to RX
body: <p>currently i try to get into thinking the Reactive Extensions way, by only send one way messages from components. But i still havent figuered out how to implement something with CancelableEventArgs that relies on the synchronous execution of the registered handlers into a solution that works with rx.</p>
  
  <p>Example:</p>
  
  <pre><code>public void Delete()
  {
      var deleteRequest = new DeleteServerRequest(_serverConfigurationMapper.Map(SelectedServer)); 
      _eventStream.Push(deleteRequest);
      if (!deleteRequest.Cancel)
          _serverConfigurationRepository.Delete(deleteRequest.Server);
  }
  </code></pre>
  
  <p>In another class i register on the DeleteServerRequest and show a prompt so the user is able to cancel the deletion of the item.</p>
  
  <pre><code>_eventStream.Of&lt;DeleteServerRequest&gt;().Subscribe(
      req =&gt;
        req.Cancel = DilaogResult.Yes != MessageBox.Show("Delte Server?", 
                                                         "Do you want to delete the server?",
                                                         MessageBoxButtons.YesNo))
  </code></pre>
  
  <p>How would i do something like this with only one directional messaging like in RX?</p>
  
  <p>PS: 
  The Delete method is the implementation of a command in a ViewModel, so i didn't want to bring UI-Framework code into it.
  The EventHandler is in a controller, that only should show and close the different windows and dialogs.</p>