Here is an improved version of the above mentioned attached behavior. It fully supports twoway binding and also works with HeriarchicalDataTemplate
and TreeView
s where its items are virtualized. Please note though that to find the 'TreeViewItem' that needs to be selected, it will realize (i.e. create) the virtualized TreeViewItem
s until it finds the right one. This could potentially be a performance problem with big virtualized trees.
public class BindableSelectedItemBehavior : Behavior<TreeView>
{
public static readonly DependencyProperty SelectedItemProperty =
DependencyProperty.Register(
"SelectedItem",
typeof(object),
typeof(BindableSelectedItemBehavior),
new UIPropertyMetadata(null, OnSelectedItemChanged));
public object SelectedItem
{
get
{
return this.GetValue(SelectedItemProperty);
}
set
{
this.SetValue(SelectedItemProperty, value);
}
}
protected override void OnAttached()
{
base.OnAttached();
this.AssociatedObject.SelectedItemChanged += this.OnTreeViewSelectedItemChanged;
}
protected override void OnDetaching()
{
base.OnDetaching();
if (this.AssociatedObject != null)
{
this.AssociatedObject.SelectedItemChanged -= this.OnTreeViewSelectedItemChanged;
}
}
private static Action<int> GetBringIndexIntoView(Panel itemsHostPanel)
{
var virtualizingPanel = itemsHostPanel as VirtualizingStackPanel;
if (virtualizingPanel == null)
{
return null;
}
var method = virtualizingPanel.GetType().GetMethod(
"BringIndexIntoView",
BindingFlags.Instance | BindingFlags.NonPublic,
Type.DefaultBinder,
new[] { typeof(int) },
null);
if (method == null)
{
return null;
}
return i => method.Invoke(virtualizingPanel, new object[] { i });
}
private static TreeViewItem GetTreeViewItem(ItemsControl container, object item)
{
if (container != null)
{
if (container.DataContext == item)
{
return container as TreeViewItem;
}
if (container is TreeViewItem && !((TreeViewItem)container).IsExpanded)
{
container.SetValue(TreeViewItem.IsExpandedProperty, true);
}
container.ApplyTemplate();
var itemsPresenter =
(ItemsPresenter)container.Template.FindName("ItemsHost", container);
if (itemsPresenter != null)
{
itemsPresenter.ApplyTemplate();
}
else
{
itemsPresenter = container.GetVisualDescendant<ItemsPresenter>();
if (itemsPresenter == null)
{
container.UpdateLayout();
itemsPresenter = container.GetVisualDescendant<ItemsPresenter>();
}
}
var itemsHostPanel = (Panel)VisualTreeHelper.GetChild(itemsPresenter, 0);
#pragma warning disable 168
var children = itemsHostPanel.Children;
#pragma warning restore 168
var bringIndexIntoView = GetBringIndexIntoView(itemsHostPanel);
for (int i = 0, count = container.Items.Count; i < count; i++)
{
TreeViewItem subContainer;
if (bringIndexIntoView != null)
{
bringIndexIntoView(i);
subContainer =
(TreeViewItem)container.ItemContainerGenerator.
ContainerFromIndex(i);
}
else
{
subContainer =
(TreeViewItem)container.ItemContainerGenerator.
ContainerFromIndex(i);
subContainer.BringIntoView();
}
if (subContainer == null)
{
continue;
}
var resultContainer = GetTreeViewItem(subContainer, item);
if (resultContainer != null)
{
return resultContainer;
}
subContainer.IsExpanded = false;
}
}
return null;
}
private static void OnSelectedItemChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
var item = e.NewValue as TreeViewItem;
if (item != null)
{
item.SetValue(TreeViewItem.IsSelectedProperty, true);
return;
}
var behavior = (BindableSelectedItemBehavior)sender;
var treeView = behavior.AssociatedObject;
if (treeView == null)
{
return;
}
item = GetTreeViewItem(treeView, e.NewValue);
if (item != null)
{
item.IsSelected = true;
}
}
private void OnTreeViewSelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
this.SelectedItem = e.NewValue;
}
}
And for the sake of completeness hier is the implementation of GetVisualDescentants
:
public static class DependencyObjectExtensions
{
public static T GetVisualDescendant<T>(this DependencyObject visual) where T : DependencyObject
{
return (T)visual.GetVisualDescendants().FirstOrDefault(d => d is T);
}
public static IEnumerable<DependencyObject> GetVisualDescendants(this DependencyObject visual)
{
if (visual == null)
{
yield break;
}
for (var i = 0; i < VisualTreeHelper.GetChildrenCount(visual); i++)
{
var child = VisualTreeHelper.GetChild(visual, i);
yield return child;
foreach (var subChild in GetVisualDescendants(child))
{
yield return subChild;
}
}
}
}