Listview inside of scrollviewer prevents scrollviewer scroll

Question

I have a scrollviewer with a couple listboxes in it. The problem is if a user uses the middle mouse roller to scroll the scrollviewer while their mouse is over a listview. T

Answer 1

Inspired by some helpful answers, I have an implementation that scrolls ancestor ScrollViewers when inner ones (including from ListView, ListBox, DataGrid) scroll past their top/bottom.

I apply an attached property to all ScrollViewers in App.xaml:

The attached property detects scrolling past top/bottom, and when that happens raises a mouse wheel event on the ScrollViewer's parent. Event routing gets it to the outer ScrollViewer:

public static class ScrollViewerHelper
{
    // Attached property boilerplate
    public static bool GetFixMouseWheel(ScrollViewer scrollViewer) => (bool)scrollViewer?.GetValue(FixMouseWheelProperty);
    public static void SetFixMouseWheel(ScrollViewer scrollViewer, bool value) => scrollViewer?.SetValue(FixMouseWheelProperty, value);
    public static readonly DependencyProperty FixMouseWheelProperty =
        DependencyProperty.RegisterAttached("FixMouseWheel", typeof(bool), typeof(ScrollViewerHelper),
            new PropertyMetadata(OnFixMouseWheelChanged));
    // End attached property boilerplate

    static void OnFixMouseWheelChanged(DependencyObject d,
                                       DependencyPropertyChangedEventArgs e)
    {
        var scrollViewer = d as ScrollViewer;
        if (scrollViewer == null) return;

        scrollViewer.PreviewMouseWheel += (s2, e2) =>
        {
            var parent = scrollViewer.Parent as UIElement;
            bool hitTopOrBottom = HitTopOrBottom(e2.Delta, scrollViewer);
            if (parent is null || !hitTopOrBottom) return;

            var argsCopy = Copy(e2);
            parent.RaiseEvent(argsCopy);
        };
    }

    static bool HitTopOrBottom(double delta, ScrollViewer scrollViewer)
    {
        var contentVerticalOffset = scrollViewer.ContentVerticalOffset;

        var atTop = contentVerticalOffset == 0;
        var movedUp = delta > 0;
        var hitTop = atTop && movedUp;

        var atBottom =
            contentVerticalOffset == scrollViewer.ScrollableHeight;
        var movedDown = delta < 0;
        var hitBottom = atBottom && movedDown;

        return hitTop || hitBottom;
    }

    static MouseWheelEventArgs Copy(MouseWheelEventArgs e)
        => new MouseWheelEventArgs(e.MouseDevice, e.Timestamp, e.Delta)
        {
            RoutedEvent = UIElement.MouseWheelEvent,
            Source = e.Source,
        };
}