For example, I made a floating searchbar with transparent frame, and a RadListView with HeaderTemplate that can be longer than one or two screen height of the device. At the end of the page is a scrollable product listing that will kept on load more products on demand.

I would like to detect the scroll position of the ListView, so if the scroll Y is more than 10px vertically, I can change the color of the toolbar to my desired color.

Using ItemAppearing event won't be able to achieve as user will need to scroll until more than 2 screen height of device only will trigger the first item.

ScrollView provide Scrolled event, but I can't use the ScrollView wrapping the content and the RadListView as it will mess up the scroll of the RadListView.

Placing ScrollView wrapping the content, next to a RadListView is also not an option as it will be come 2 scroll content at seperated section.

That's why the only choice is to place content inside the HeaderTemplate so we can achieve a fully scrollable page, and infinite product listing at the bottom.

Enable Scrolled event and info allow developer to do all sort's of things like animation, or showing info on a certain scrolling position.

For example, you can check this out. Something you can do with the "Scrolled" event on CarouselView. It's a different control, but you can see similar thing can be done with the ListView with Scrolled event as well.