Introduction to Attached Behaviors in WPF - CodeProject
<TreeView.ItemContainerStyle>
<Style TargetType="{x:Type TreeViewItem}">
<!--
This Setter applies an attached behavior to all TreeViewItems.
-->
<Setter
Property="local:TreeViewItemBehavior.IsBroughtIntoViewWhenSelected"
Value="True"
/>
<!--
These Setters bind a TreeViewItem to a PersonViewModel.
-->
<Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
<Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}" />
<Setter Property="FontWeight" Value="Normal" />
<Style.Triggers>
<Trigger Property="IsSelected" Value="True">
<Setter Property="FontWeight" Value="Bold" />
</Trigger>
</Style.Triggers>
</Style>
</TreeView.ItemContainerStyle>
/// <summary>
/// Exposes attached behaviors that can be
/// applied to TreeViewItem objects.
/// </summary>
public static class TreeViewItemBehavior
{
#region IsBroughtIntoViewWhenSelected
public static bool GetIsBroughtIntoViewWhenSelected(TreeViewItem treeViewItem)
{
return (bool)treeViewItem.GetValue(IsBroughtIntoViewWhenSelectedProperty);
}
public static void SetIsBroughtIntoViewWhenSelected(
TreeViewItem treeViewItem, bool value)
{
treeViewItem.SetValue(IsBroughtIntoViewWhenSelectedProperty, value);
}
public static readonly DependencyProperty IsBroughtIntoViewWhenSelectedProperty =
DependencyProperty.RegisterAttached(
"IsBroughtIntoViewWhenSelected",
typeof(bool),
typeof(TreeViewItemBehavior),
new UIPropertyMetadata(false, OnIsBroughtIntoViewWhenSelectedChanged));
static void OnIsBroughtIntoViewWhenSelectedChanged(
DependencyObject depObj, DependencyPropertyChangedEventArgs e)
{
TreeViewItem item = depObj as TreeViewItem;
if (item == null)
return;
if (e.NewValue is bool == false)
return;
if ((bool)e.NewValue)
item.Selected += OnTreeViewItemSelected;
else
item.Selected -= OnTreeViewItemSelected;
}
static void OnTreeViewItemSelected(object sender, RoutedEventArgs e)
{
// Only react to the Selected event raised by the TreeViewItem
// whose IsSelected property was modified. Ignore all ancestors
// who are merely reporting that a descendant's Selected fired.
if (!Object.ReferenceEquals(sender, e.OriginalSource))
return;
TreeViewItem item = e.OriginalSource as TreeViewItem;
if (item != null)
item.BringIntoView();
}
#endregion // IsBroughtIntoViewWhenSelected
}
public class TreeViewHelper
{
private static Dictionary<DependencyObject, TreeViewSelectedItemBehavior> behaviors = new Dictionary<DependencyObject, TreeViewSelectedItemBehavior>();
public static object GetSelectedItem(DependencyObject obj)
{
return (object)obj.GetValue(SelectedItemProperty);
}
public static void SetSelectedItem(DependencyObject obj, object value)
{
obj.SetValue(SelectedItemProperty, value);
}
// Using a DependencyProperty as the backing store for SelectedItem. This enables animation, styling, binding, etc...
public static readonly DependencyProperty SelectedItemProperty =
DependencyProperty.RegisterAttached("SelectedItem", typeof(object), typeof(TreeViewHelper), new UIPropertyMetadata(null, SelectedItemChanged));
private static void SelectedItemChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
{
if (!(obj is TreeView))
return;
if (!behaviors.ContainsKey(obj))
behaviors.Add(obj, new TreeViewSelectedItemBehavior(obj as TreeView));
TreeViewSelectedItemBehavior view = behaviors[obj];
view.ChangeSelectedItem(e.NewValue);
}
private class TreeViewSelectedItemBehavior
{
TreeView view;
public TreeViewSelectedItemBehavior(TreeView view)
{
this.view = view;
view.SelectedItemChanged += (sender, e) => SetSelectedItem(view, e.NewValue);
}
internal void ChangeSelectedItem(object p)
{
TreeViewItem item = (TreeViewItem)view.ItemContainerGenerator.ContainerFromItem(p);
item.IsSelected = true;
}
}
}
<TreeView ItemsSource="{Binding Path=Root.Children}"
local:TreeViewHelper.SelectedItem="{Binding Path=SelectedItem, Mode=TwoWay}"/>