WPF Nested Scrollviewers - giving control back to parent scollviewer - wpf

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.