Prevent Automatic Horizontal Scroll in TreeView

Question

Whenever a node is selected in my treeview, it automatically does a horizontal scroll to that item. Is there a way to disable this?

Answer 1

I had a DataGrid that I wanted to do the same operation on and used POHB's answer mostly. I had to modify it for my solution. The code is shown below. The datagrid is a 2 x 2 datagrid with the first column being thin and the second being very wide (1000+). The first column is frozen. I hope this helps someone out. -Matt

  public partial class MyUserControl : UserControl
  {
      private ScrollContentPresenter _scrollContentPresenter;
      private ScrollViewer _scrollViewer;
      private double _dataGridHorizScrollPos = 0.0;
      private bool _dataGridResetHorizScroll = false;

      public MyUserControl()
      {
          // setup code...
          _dataGrid.ApplyTemplate();

          _scrollViewer = FindVisualChild<ScrollViewer>(_dataGrid);
          _scrollViewer.ScrollChanged += new ScrollChangedEventHandler(DataGridScrollViewerScrollChanged);

          _scrollContentPresenter = FindVisualChild<ScrollContentPresenter>(_scrollViewer);
          _scrollContentPresenter.RequestBringIntoView += new RequestBringIntoViewEventHandler(_scrollContentPresenter_RequestBringInputView);              
      }

      private void DataGridScrollViewerScrollChanged(object sender, ScrollChangedEventArgs e)
      {
          if (_dataGridResetHorizScroll)
          {
              _scrollViewer.ScrollToHorizontalOffset(_dataGridHorizScrollPos);
          }
          // Note: When the row just before a page change is selected and then the next row on the  
          // next page is selected, a second event fires setting the horizontal offset to 0
          // I'm ignoring those large changes by only recording the offset when it's large. -MRB
          else if (Math.Abs(e.HorizontalChange) < 100)
          {
              _dataGridHorizScrollPos = _scrollViewer.HorizontalOffset;
          }

          _dataGridResetHorizScroll = false;
      }

      public T FindVisualChild<T>(DependencyObject depObj) where T : DependencyObject
      {
          if (depObj != null)
          {
              for (int i = 0; i < VisualTreeHelper.GetChildrenCount(depObj); i++)
              {
                  DependencyObject child = VisualTreeHelper.GetChild(depObj, i);

                  if ((child != null) && (child is ScrollViewer))
                  {
                      // I needed this since the template wasn't applied yet when 
                      // calling from  the constructor
                      (child as ScrollViewer).ApplyTemplate();
                  }

                  if (child != null && child is T)
                  {
                      return (T)child;
                  }

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

      private void _scrollContentPresenter_RequestBringInputView(object sender, RequestBringIntoViewEventArgs e)
      {
          _dataGridResetHorizScroll = true;
      }

Answer 2

To offer a slightly simplified version of @lena's answer:

To scroll vertically while preserving the horizontal scroll position, and with no unwanted side effects, in the XAML, add event handlers for RequestBringIntoView and Selected:

<TreeView>
    <TreeView.ItemContainerStyle>
        <Style TargetType="{x:Type TreeViewItem}">
            <EventSetter Event="RequestBringIntoView" Handler="TreeViewItem_RequestBringIntoView"/>
            <EventSetter Event="Selected" Handler="OnSelected"/>
            ...

In the code behind, add two event handlers:

private void TreeViewItem_RequestBringIntoView(object sender, RequestBringIntoViewEventArgs e)
{
    // Ignore re-entrant calls
    if (mSuppressRequestBringIntoView)
        return;

    // Cancel the current scroll attempt
    e.Handled = true;

    // Call BringIntoView using a rectangle that extends into "negative space" to the left of our
    // actual control. This allows the vertical scrolling behaviour to operate without adversely
    // affecting the current horizontal scroll position.
    mSuppressRequestBringIntoView = true;

    TreeViewItem tvi = sender as TreeViewItem;
    if (tvi != null)
    {
        Rect newTargetRect = new Rect(-1000, 0, tvi.ActualWidth + 1000, tvi.ActualHeight);
        tvi.BringIntoView(newTargetRect);
    }

    mSuppressRequestBringIntoView = false;
}
private bool mSuppressRequestBringIntoView;

// Correctly handle programmatically selected items
private void OnSelected(object sender, RoutedEventArgs e)
{
    ((TreeViewItem)sender).BringIntoView();
    e.Handled = true;
}