Child/Parent ScrollViewer Scrolling Helper

[michael-hawker]

Problem Statement

We see this a lot in our sample app, but other apps and other sample galleries (like the WinUI Gallery) have this issue. Where we have nested ScrollViewer controls in order to show code/examples embedded within a larger document.

When you start scrolling the page with a mouse wheel, you can then have your mouse go over one of these inner scrollviewers and start scrolling that instead. Once you reach the bottom it doesn't continue scrolling the page beyond that unless you move your mouse outside the child scrollviewer.

Idea

Would be nice if we could detect this top/bottom scrollpoint of the inner scrollviewer and start moving the parent scrollviewer instead.

Basically have an attached property helper in the Toolkit: ScrollViewerHelper.ScrollToParent="True" to put on an inner scrollviewer make it so if you continue to scroll wheel and at the top/bottom of the viewport that it scrolls the parent viewport instead.

Additional Info

We thought ScrollViewer.IsVerticalScrollChainingEnabled would handle this scenario already, as it sounds like it should, but it does not:

The ScrollViewer's chaining properties (IsHorizontalScrollChainingEnabled,IsVerticalScrollChainingEnabled, IsZoomChainingEnabled ) do not apply when the control is in inertial mode. Because mouse wheel rotations are handled as inertial manipulations, chaining does not work.