WPF Nested Scrollviewers - giving control back to parent scollviewer

Question

This is what my control tree looks like:

<window>
 <scrollviewer>
  <expander>
   <scrollviewer>
    <grid>
    </grid>
   </scrollviewer>
  </expander>
  <expander>
   <scrollviewer>
    <grid>
    </grid>
   </scrollviewer>
  </expander>
 </scrollviewer>
</window>

Using the mouse wheel, the control automatically passes from parent to child scrollviewer, but when I scroll to the end of the child scrollviewer the control doesn't pass back to the parent scorllviewer. How do I achieve this?

The expander, grid and the scrollviewers are dynamically generated.

Answer 1

I get a similar trouble in my application. I correct it by a depency property that will catch and pass the event too his parent. This can be applied to any control that have a scroll in it. But for me, i didn't need to validate if it was at the end of the scroll to send to his parent. You will just have to add, in the OnValueChanged method, a validation for if the scroll is at the end or at the top to send to his parent.

using System.Windows.Controls;

public static class SendMouseWheelToParent
{
   public static readonly DependencyProperty ScrollProperty
     = DependencyProperty.RegisterAttached("IsSendingMouseWheelEventToParent",
        typeof(bool),
        typeof(SendMouseWheelToParent),
        new FrameworkPropertyMetadata(OnValueChanged));

   /// <summary>
   /// Gets the IsSendingMouseWheelEventToParent for a given <see cref="TextBox"/>.
   /// </summary>
   /// <param name="control">
   /// The <see cref="TextBox"/> whose IsSendingMouseWheelEventToParent is to be retrieved.
   /// </param>
   /// <returns>
   /// The IsSendingMouseWheelEventToParent, or <see langword="null"/>
   /// if no IsSendingMouseWheelEventToParent has been set.
   /// </returns>
   public static bool? GetIsSendingMouseWheelEventToParent(Control control)
   {
       if (control == null)
           throw new ArgumentNullException("");

       return control.GetValue(ScrollProperty) as bool?;
   }

   /// <summary>
   /// Sets the IsSendingMouseWheelEventToParent for a given <see cref="TextBox"/>.
   /// </summary>
   /// <param name="control">
   /// The <see cref="TextBox"/> whose IsSendingMouseWheelEventToParent is to be set.
   /// </param>
   /// <param name="IsSendingMouseWheelEventToParent">
   /// The IsSendingMouseWheelEventToParent to set, or <see langword="null"/>
   /// to remove any existing IsSendingMouseWheelEventToParent from <paramref name="control"/>.
   /// </param>
   public static void SetIsSendingMouseWheelEventToParent(Control control, bool? sendToParent)
   {
       if (control == null)
           throw new ArgumentNullException("");

       control.SetValue(ScrollProperty, sendToParent);
   }

   private static void OnValueChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
   {
       var scrollViewer = dependencyObject as Control;
       bool? IsSendingMouseWheelEventToParent = e.NewValue as bool?;
       scrollViewer.PreviewMouseWheel -= scrollViewer_PreviewMouseWheel;

       if (IsSendingMouseWheelEventToParent != null && IsSendingMouseWheelEventToParent != false)
       {
         scrollViewer.SetValue(ScrollProperty, IsSendingMouseWheelEventToParent);
         scrollViewer.PreviewMouseWheel += scrollViewer_PreviewMouseWheel;
       }
   }


   private static void scrollViewer_PreviewMouseWheel(object sender, MouseWheelEventArgs e)
   {
       var scrollview = sender as Control;

       var eventArg = new MouseWheelEventArgs(e.MouseDevice, e.Timestamp, e.Delta);
       eventArg.RoutedEvent = UIElement.MouseWheelEvent;
       eventArg.Source = sender;
       var parent = scrollview.Parent as UIElement;
       parent.RaiseEvent(eventArg);
   }
}

Answer 2

Inspired by Janick's answer and some others, I have an implementation that scrolls ancestor ScrollViewers when inner ones (including from ListView, ListBox, DataGrid) scroll past their top/bottom. The code is in my answer here to a very similar question.