Hello,

What style do you have the UltraExplorerBar set to?  I made a small sample and tried with several different styles and I found that with some styles, you have to click on the control in order for the mouse wheel to scroll the tree.  The only code I wrote was to populate the UltraTree with 100 nodes.

Also, I made my sample using 10.2.20102.2058.  If clicking on the UltraTree doesn't allow scrolling, try it with a newer version of our product.

First, trap mouse wheel messages and forward to control, which is hovered. Like so: http://social.msdn.microsoft.com/Forums/windows/en-US/eb922ed2-1036-41ca-bd15-49daed7b637c/outlookstyle-wheel-mouse-behavior

Then, attach to UltraExplorerBar.MouseWheel event and manually invoke scrolling. Since API is not exposed (or I haven't got time to find it), I used reflections. Here is event handler code:

private void HandleExplorerBarMouseWheel(object sender, MouseEventArgs e)
{
    // If there is selected group:
    if (this.explorerBar.SelectedGroup != null)
    {
        // Invoke scroll method:
        Type type = typeof(UltraExplorerBarGroup);
        MethodInfo scrollMethod =
            type.GetMethod("DoVerticalScroll_Listbar", BindingFlags.Instance | BindingFlags.NonPublic, null, new Type[1] { typeof(ScrollEventType) }, null);
        if (scrollMethod != null)
            scrollMethod.Invoke(this.explorerBar.SelectedGroup,
                new object[1]
                {
                    e.Delta > 0
                        ? ScrollEventType.SmallDecrement
                        : ScrollEventType.SmallIncrement
                });
    }
}