title: How do I get a `BindingExpression` from a `Binding` object?
body: <p>In short(?), I have a <code>ListView</code> (target) one-way bound to an <code>XmlDataProvider</code> (source) two-way bound to a <code>TextBox</code> (target) using standard XAML for the control bindings and custom XAML extensions for the bindings to the <code>XmlDataProvider</code>.  This is a convenience for the application as the <code>XmlDataProvider</code> is dynamically loaded from user inputs after the application is running,...</p>
  
  <p>Anyway, at run-time, after modifying the <code>TextBox.Text</code> property, the <code>IMultiValueConverter.ConvertBack(...)</code> method is called to propagate the update from this target back to the source.  But, because the <code>XmlDataProvider</code> object is not a <code>DependencyProperty</code>, the update is not further propagated from the changed <code>XmlDataProvider</code> source to the other binding to the <code>ListView</code> target.</p>
  
  <p>Without rearchitecting, which you could legitimately advise, I need to notify WPF that any target with this <code>XmlDataProvider</code> as a source needs to be updated.  I am hoping to maintain a generic, reusable binding class and have, so far, enjoyed the low coding burden of my mostly XAML solution.</p>
  
  <p>Currently, the only code behind access I have is from within the <code>IMultiValueConverter.ConvertBack(...)</code> method.  From within this method I do have access to the <code>Binding</code> object for the <code>XmlDataProvider</code> &lt;--&gt; <code>TextBox</code> link.  If I could get the <code>BindingExpression</code> for the <code>Binding.Source</code> object I could then make the call to <code>BindingExpression.UpdateTarget()</code> to complete the update propagation,...</p>
  
  <p>But, I do not know how to get a <code>BindingExpression</code>from a <code>Binding.Source</code> object, that is not associated with a <code>DependencyProperty</code>.</p>
  
  <p>Thanks in advance for your advice and assistance.</p>