How to get TreeViewItem from HierarchicalDataTemplate item?

I ran into this same problem. I needed to get to the TreeViewItem so that I could have it be selected. I then realized that I could just add a property IsSelected to my ViewModel, which I then bound to the TreeViewItems IsSelectedProperty. This can be achieved with the ItemContainerStyle:

<TreeView>
            <TreeView.ItemContainerStyle>
                <Style TargetType="{x:Type TreeViewItem}">
                    <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}"/>
                    <Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}" />
                </Style>
            </TreeView.ItemContainerStyle>
</TreeView>

Now if I want to have an item in the treeview selected, I just call IsSelected on my ViewModel class directly.

Hope it helps someone.

TreeViewItem item = (TreeViewItem)(mainTreeList
    .ItemContainerGenerator
    .ContainerFromIndex(mainTreeList.Items.CurrentPosition));

DOES NOT WORK (for me) as mainTreeList.Items.CurrentPosition in a treeview using a HierarchicalDataTemplate will always be -1.

NEITHER DOES below as as mainTreeList.Items.CurrentItem in a treeview using a HierarchicalDataTemplate will always be null.

TreeViewItem item = (TreeViewItem)mainTreeList
    .ItemContainerGenerator
    .ContainerFromItem(mainTreeList.Items.CurrentItem);

INSTEAD I had to set a the last selected TreeViewItem in the routed TreeViewItem.Selected event which bubbles up to the tree view (the TreeViewItem's themselves do not exist at design time as we are using a HierarchicalDataTemplate).

The event can be captured in XAML as so:

<TreeView TreeViewItem.Selected="TreeViewItemSelected" .../> 

Then the last TreeViewItem selected can be set in the event as so:

    private void TreeViewItemSelected(object sender, RoutedEventArgs e)
    {
        TreeViewItem tvi = e.OriginalSource as TreeViewItem;

        // set the last tree view item selected variable which may be used elsewhere as there is no other way I have found to obtain the TreeViewItem container (may be null)
        this.lastSelectedTreeViewItem = tvi;

        ...
     }

From Bea Stollnitz's blog entry about this, try

TreeViewItem item = (TreeViewItem)(mainTreeList
    .ItemContainerGenerator
    .ContainerFromIndex(mainTreeList.Items.CurrentPosition));