title: Accessing additional context data in EditValue of UITypeEditor
body: <p>I'm tweaking a WinForms application.  This application has a <code>Form</code> that contains a <code>PropertyGrid</code>.  An object is assigned to the <code>SelectedObject</code> property so that the property grid displays the properties for the object.</p>
  
  <p>The type of the object assigned has a property that carries an <code>EditorAttribute</code> specifying a <code>UITypeEditor</code>.</p>
  
  <p>This implementation of <code>UITypeEditor</code> returns <code>UITypeEditorEditStyle.Drop</code> in its override of <code>GetEditStyle</code> method.   Its <code>EditValue</code> method displays a <code>ListBox</code> from which a value for the instance property can be assigned.</p>
  
  <p>All well an good so far.</p>
  
  <p>Now I have an additional requirement which calls for the available items in the list to be modified based on other state held by the <code>Form</code> hosting the <code>PropertyGrid</code>.  I can't work out how to get this contextual information to the <code>EditValue</code> method.</p>
  
  <p>There doesn't seem to be anything on the <code>context</code> parameter even if I try casting it to more specific types.  Neither can I work out how to add some other Service to retrieve from the <code>provider</code>.</p>
  
  <p>Any ideas?</p>