Vista - Ensuring expanded

I'm using the HierarchicalDataTemplate to populate my TreeView. The downside
to this is that myTreeView.SelectedItem returns the actual data and NOT the
TreeViewItem object associated with the data. The problem with this is that
it is difficult to set properties on the TreeViewItem associated with deeply
nested data items. This is a real problem, as I'm am trying to ensure that
new nodes generated under a parent are visible, so I'd like to set the
parent's TreeViewItem.IsExpanded property to true. The trick is getting that
TreeViewItem! This code works when creating nodes for the first / root
items, but then second Debug.Assert trips when creating nodes for sub nodes:

private void CheckSelectedItem( bool isChecked )
{
Debug.Assert( mProjectTree != null );
object selectedItem = mProjectTree.SelectedItem;

if( selectedItem != null && mProjectTree != null )
{
TreeViewItem treeItem =
mProjectTree.ItemContainerGenerator.ContainerFromItem( selectedItem ) as
TreeViewItem;
Debug.Assert( treeItem != null );

if( treeItem != null )
{
treeItem.IsExpanded = isChecked;
}
}
}

I have tested some code that can walk up the parent hierarchy of my data in
order to find the first ItemContainerGenerator from which to start walking
down the tree, but that just seems way too difficult and cumbersome, so I
must be doing something wrong!

There is another case where this has caused me undo headaches. I wanted to
ensure that a right click in the tree selected whatever node the user
clicked on. Look at how complicated this code is!


private void OnRightButtonDown( object sender, MouseEventArgs e )
{
// All this code is needed in order to figure out what node
// the user has right clicked over!!!

if( e.MouseDevice.Target is FrameworkElement )
{
FrameworkElement element = e.MouseDevice.Target as
FrameworkElement;
System.Windows.Controls.ContentPresenter pres =
element.TemplatedParent as ContentPresenter;

if( pres != null )
{
TreeViewItem viewItem = pres.TemplatedParent as TreeViewItem;

if( viewItem == null )
{
viewItem =
mProjectTree.ItemContainerGenerator.ContainerFromItem( pres.Content ) as
TreeViewItem;
}

if( viewItem != null )
{
viewItem.IsSelected = true;
}
}
}
}

There's gotta be an easier way!

Thanks,

CS