/// <summary>
/// Behavior that makes the <see cref="System.Windows.Controls.TreeView.SelectedItem" /> bindable.
/// </summary>
internal class BindableTreeViewSelectedItemBehavior : Behavior<TreeView>
{
#region " SelectedItem "
public static readonly DependencyProperty SelectedItemProperty = DependencyProperty.Register("SelectedItem", typeof(object), typeof(BindableTreeViewSelectedItemBehavior), new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, OnSelectedItemChanged));
public object SelectedItem
{
get { return this.GetValue(SelectedItemProperty); }
set { this.SetValue(SelectedItemProperty, value); }
}
private static void OnSelectedItemChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
if (e.NewValue is TreeViewItem item)
{
item.SetValue(TreeViewItem.IsSelectedProperty, true);
item.Focus();
return;
}
if (sender is BindableTreeViewSelectedItemBehavior behavior)
{
var treeView = behavior.AssociatedObject;
if (treeView != null)
{
item = GetTreeViewItem(treeView, e.NewValue);
if (item != null)
{
item.IsSelected = true;
item.Focus();
}
}
}
}
#endregion
protected override void OnAttached()
{
base.OnAttached();
this.AssociatedObject.SelectedItemChanged += this.OnTreeViewSelectedItemChanged;
}
private void OnTreeViewSelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
this.SelectedItem = e.NewValue;
}
protected override void OnDetaching()
{
base.OnDetaching();
if (this.AssociatedObject != null)
{
this.AssociatedObject.SelectedItemChanged -= this.OnTreeViewSelectedItemChanged;
}
}
#region " GetBringIndexIntoView "
/// <summary>
/// GetBringIndexIntoView
/// </summary>
/// <param name="itemsHostPanel"></param>
/// <returns>Action<int></returns>
private static Action<int> GetBringIndexIntoView(Panel itemsHostPanel)
{
if (itemsHostPanel is VirtualizingStackPanel virtualizingPanel)
{
var method = virtualizingPanel.GetType().GetMethod("BringIndexIntoView", BindingFlags.Instance | BindingFlags.NonPublic, Type.DefaultBinder, new[] { typeof(int) }, null);
if (method != null)
{
return i => method.Invoke(virtualizingPanel, new object[] { i });
}
}
return null;
}
#endregion
#region " GetTreeViewItem "
/// <summary>
/// GetTreeViewItem
/// Recursively search for an item in this subtree.
/// </summary>
/// <param name="container">The parent ItemsControl. This can be a TreeView or a TreeViewItem.</param>
/// <param name="item">The item to search for.</param>
/// <returns>TreeViewItem</returns>
private static TreeViewItem GetTreeViewItem(ItemsControl container, object item)
{
if (container != null)
{
if (container.DataContext == item)
{
return container as TreeViewItem;
}
// Expand the current container
if (container is TreeViewItem && !((TreeViewItem)container).IsExpanded)
{
container.SetValue(TreeViewItem.IsExpandedProperty, true);
}
// Try to generate the ItemsPresenter and the ItemsPanel.
// by calling ApplyTemplate. Note that in the
// virtualizing case even if the item is marked
// expanded we still need to do this step in order to
// regenerate the visuals because they may have been virtualized away.
container.ApplyTemplate();
var itemsPresenter = (ItemsPresenter)container.Template.FindName("ItemsHost", container);
if (itemsPresenter != null)
{
itemsPresenter.ApplyTemplate();
}
else
{
// The Tree template has not named the ItemsPresenter,
// so walk the descendents and find the child.
itemsPresenter = container.GetVisualDescendant<ItemsPresenter>();
if (itemsPresenter == null)
{
container.UpdateLayout();
itemsPresenter = container.GetVisualDescendant<ItemsPresenter>();
}
}
if (itemsPresenter != null)
{
var itemsHostPanel = (Panel)VisualTreeHelper.GetChild(itemsPresenter, 0);
// Ensure that the generator for this panel has been created.
#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)
{
// Bring the item into view so
// that the container will be generated.
bringIndexIntoView(i);
subContainer = (TreeViewItem)container.ItemContainerGenerator.ContainerFromIndex(i);
}
else
{
subContainer = (TreeViewItem)container.ItemContainerGenerator.ContainerFromIndex(i);
// Bring the item into view to maintain the
// same behavior as with a virtualizing panel.
subContainer.BringIntoView();
}
if (subContainer == null)
{
continue;
}
// Search the next level for the object.
var resultContainer = GetTreeViewItem(subContainer, item);
if (resultContainer != null)
{
return resultContainer;
}
// The object is not under this TreeViewItem
// so collapse it.
subContainer.IsExpanded = false;
}
}
}
return null;
}
#endregion
}
我过去曾使用此行为来获取树视图，以便在通过绑定更改选定项以使项目滚动到视图时进行更新。你可以这样使用它：
<TreeView Grid.Column="1" Grid.Row="1" ItemsSource="{Binding MyTree}" MaxHeight="270" ScrollViewer.VerticalScrollBarVisibility="Auto" VirtualizingStackPanel.IsVirtualizing="True">
<i:Interaction.Behaviors>
<h:BindableTreeViewSelectedItemBehavior SelectedItem="{Binding SelectedTV}"></h:BindableTreeViewSelectedItemBehavior>
</i:Interaction.Behaviors>
<TreeView.ItemTemplate>
<HierarchicalDataTemplate ItemsSource="{Binding Children}" DataType="{x:Type wiz:TVTest}">
<Label Content="{Binding Name}"></Label>
<HierarchicalDataTemplate.ItemTemplate>
<HierarchicalDataTemplate ItemsSource="{Binding Children}" DataType="{x:Type wiz:TVTest}">
<Label Content="{Binding Name}"></Label>
<HierarchicalDataTemplate.ItemTemplate>
<DataTemplate DataType="{x:Type wiz:TVTest}">
<Label Content="{Binding Name}"></Label>
</DataTemplate>
</HierarchicalDataTemplate.ItemTemplate>
</HierarchicalDataTemplate>
</HierarchicalDataTemplate.ItemTemplate>
</HierarchicalDataTemplate>
</TreeView.ItemTemplate>
</TreeView>
然后您可以将所选项目设置为树视图中的第一项，它应该滚动到顶部。
这里是辅助函数：
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 (int i = 0; i < VisualTreeHelper.GetChildrenCount(visual); i++)
{
DependencyObject child = VisualTreeHelper.GetChild(visual, i);
yield return child;
if (VisualTreeHelper.GetChildrenCount(child) == 0)
{
continue;
}
foreach (DependencyObject subChild in GetVisualDescendants(child))
{
yield return subChild;
}
}
}