private static void OnScrollViewerPreviewMouseWheel(object sender, MouseWheelEventArgs e)
{
var scrollViewer = sender as ScrollViewer;
// We only want to process the PreviewMouseWheel event in the following cases:
// The event was not previously handled
// The event is a fake event OR the first time we receive an original event
// The current ScrollViewer was not already processed
if (!e.Handled && !e.Equals(s_currentOriginalEventArg) && (scrollViewer != null) &&
(s_sequence == null || (!s_sequence.ScrollViewers.Contains(scrollViewer) && s_sequence.FakeEvents.Contains(e))))
{
// Create our fake event that will be used to parse all the children ScrollViewers
var previewEventArg = new MouseWheelEventArgs(e.MouseDevice, e.Timestamp, e.Delta)
{
RoutedEvent = UIElement.PreviewMouseWheelEvent,
Source = e.OriginalSource,
};
var originalSource = e.OriginalSource as IInputElement;
if (originalSource != null)
{
if (s_sequence == null)
{
// First time through the sequence, this only happen the first time we receive the original event
s_sequence = new ScrollViewerBehaviorSequence(e, scrollViewer, previewEventArg);
s_currentOriginalEventArg = e;
}
else
{
s_sequence.FakeEvents.Add(previewEventArg);
s_sequence.ScrollViewers.Add(scrollViewer);
}
// Raise the fake event on the original source, so that it is pushed all the way down the logical tree to all the
// ScrollViewers (this is done recursively by each child)
originalSource.RaiseEvent(previewEventArg);
// Now that all the children ScrollViewers raised their own fake event, we can start going back up the chain
if (s_sequence.FakeEvents.Contains(e))
{
if (previewEventArg.Handled)
{
// If one of our children already handled our fake event, handle them all the way up
e.Handled = true;
}
else
{
// At this point if no one else handled the event in our children, we do our job
if (IsScrollSupported(scrollViewer))
{
// If this ScrollViewer is able to scroll, handle the fake events all the way up
e.Handled = true;
}
if (IsScrollingOutOfBounds(scrollViewer, e.Delta))
{
// If this ScrollViewer has reached its upper or lower bound, push a MouseWheelEvent on a parent
// ScrollViewer that can handle it
s_sequence.ForceMouseWheelEvent(scrollViewer, e);
}
}
}
// Remove the current instances of ScrollViewer and fake event from the sequence
s_sequence.FakeEvents.Remove(previewEventArg);
s_sequence.ScrollViewers.Remove(scrollViewer);
if (s_sequence.FakeEvents.Count == 0)
{
s_sequence = null;
}
}
}
}