title: How to let caliburn.micro know to reattach actions when cal:Bind.Model is pointed to new a object instance?
body: <p>I have a simple use case which I am struggling with in Caliburn.Micro. I can get this to work easily with traditional bindings, but I'd like to use the framework properly. </p>
  
  <p>In short, this is an MDI style app with a single top level toolbar of which I'd like to bind the context to the Conductor.ActiveItem. Basically, the issue I'm seeing is that Calibun set up the Actions for the toolbar buttons for the first opened tab, but later when ActiveItem is changed, the connected actions continue to point to the first assigned ActiveItem and not the new one.</p>
  
  <p>My main ViewModel is of type Conductor.Collection.OneActive. </p>
  
  <pre><code>public sealed class MainViewModel : Conductor&lt;ITabPage&gt;.Collection.OneActive
  {
  }
  </code></pre>
  
  <p>This view model contains a simple list of tabs each with public methods Save() and Undo() (along with bool property implementations for CanSave and CanUndo).</p>
  
  <pre><code>public interface ITabPage : IScreen, IDisposable
  {
      void Save();
      void Undo();
      bool CanSave { get; }
      bool CanUndo { get; }        
  }
  </code></pre>
  
  <p>Now the view contains the top-level toolbar with buttons invoking the actions on the ActiveItem and a TabControl to display the conductor items.</p>
  
  <pre><code>&lt;Window xmlns:cal="http://www.caliburnproject.org" ...&gt;
      &lt;DockPanel&gt;
          &lt;ToolBar DockPanel.Dock="Top" cal:Bind.Model="{Binding ActiveItem}"&gt;
              &lt;Button Name="Save"&gt;Save&lt;/Button&gt;
              &lt;Button Name="Undo"&gt;Undo&lt;/Button&gt;
          &lt;/ToolBar&gt;
          &lt;TabControl x:Name="Items"&gt;
          &lt;/TabControl&gt;
      &lt;/DockPanel&gt;
  &lt;/Window&gt;
  </code></pre>
  
  <p>Using normal binding and ICommands works fine, but I'd like to not fight the framework on this. Is there something I'm missing or misusing with cal:Bind.Model? Or perhaps a way to let it know to refresh? I've also tried calling Refresh() when ActiveItem is changed and I'm *absolutely" sure the CanSave and CanUndo are notifying properly (I've set break points and I've had success with normal bindings.)</p>