Binding FocusedElement in HierarchicalDataTemplate

Question

I am trying to focus a control within a HierarchicalDataTemplate. Unfortunately, my attempt to bind to a control within the template is failing. Here is my code:

        <HierarchicalDataTemplate DataType="{x:Type TreeView_Experiment:BookmarkPage}">
            <DockPanel>
                <ToggleButton ... edited for brevity ... />
                <Controls:EditableTextBlock x:Name="EditBox" Text="{Binding Path=Title}" VerticalAlignment="Center" IsEditable="True" Focusable="True"/>
            </DockPanel>
            <HierarchicalDataTemplate.Triggers>
                <DataTrigger Binding="{Binding Path=IsFocused, RelativeSource={RelativeSource AncestorType={x:Type TreeViewItem}}}" Value="true">
                    <!-- The Value binding fails with the error: Cannot find source for binding with reference 'ElementName=EditBox -->
                    <Setter Property="FocusManager.FocusedElement" Value="{Binding ElementName=EditBox}"/>
                </DataTrigger>
            </HierarchicalDataTemplate.Triggers>
        </HierarchicalDataTemplate>

The trigger fires when the treeview item gets the focus, but the {Binding ElementName=EditBox} fails with the message "Cannot find source for binding with reference 'ElementName=EditBox,..."

How can I fix this binding? Or is there a better way to set the focus of a control within a HierarchicalDataTemplate?

Thanks in advance for any help.

score 0 · Answer 1 · answered Nov 18 '12 at 00:18

0

Instead of looking at the TreeView and trying to find the item to focus, it may be better to have the TreeViewItem itself do the focusing.

answered Nov 18 '12 at 00:18

stricq

798
6
18

score 0 · Accepted Answer · answered Mar 18 '11 at 16:44

I was able to get this working by adding this ugly little bit of code behind. Attach this to the treeview's onselection changed:

    private void SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
    {
        var treeView = sender as TreeView;

        var selectedContainer =
            typeof (TreeView).GetProperty("SelectedContainer", BindingFlags.NonPublic | BindingFlags.Instance).
                GetValue(treeView, null) as TreeViewItem;

        // Find the element we want to focus.
        var focusControl = selectedContainer.FindVisualChild<TextBox>();
        if (focusControl != null)
            focusControl.Focus();
    }

The following extension method is required:

    public static T FindVisualChild<T>(this DependencyObject obj) where T : DependencyObject
    {
        var childCount = VisualTreeHelper.GetChildrenCount(obj);
        for (int i = 0; i < childCount; i++)
        {
            DependencyObject child = VisualTreeHelper.GetChild(obj, i);
            if (child != null && child is T)
            {
                return (T)child;
            }

            T childOfChild = FindVisualChild<T>(child);
            if (childOfChild != null)
            {
                return childOfChild;
            }
        }
        return null;
    }

Binding FocusedElement in HierarchicalDataTemplate

2 Answers2