title: How to handle windows event (message) the ReactiveUI way?
body: <p>I'm new to ReactiveUI and currently happy with it.
  But I have one question: How to handle windows event/message the ReactiveUI way?</p>
  
  <p>In mvvmlight, it's like this:</p>
  
  <pre><code>&lt;Window ...
      xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
      xmlns:command="http://www.galasoft.ch/mvvmlight"&gt;
  &lt;i:Interaction.Triggers&gt;
    &lt;i:EventTrigger EventName="Closing"&gt;
      &lt;command:EventToCommand Command="{Binding ClosingCommand}"
                          PassEventArgsToCommand="True" /&gt;
    &lt;/i:EventTrigger&gt;
  &lt;/i:Interaction.Triggers&gt;
  </code></pre>
  
  <p>But I don't know how to do it in ReactiveUI.
  Maybe it's something similar to </p>
  
  <pre><code>MessageBus.Current.Listen&lt;KeyUpEventArgs&gt;()  
      .Where(e =&gt; e.KeyCode == KeyCode.Up)
      .Subscribe(x =&gt; Console.WriteLine("Up Pressed!"));
  </code></pre>
  
  <p>but I don't know how to do it for mainframe's <code>Closing</code> event specifically.</p>
  
  <p>I have read somewhere that the author of ReactiveUI is not strongly against <em>code behind</em> code (maybe I remember wrong), what's the suggested way then? </p>