LongListSelector interaction breaks when a popup is open in WP8

Question

To dynamically place some content on a page in a Windows Phone 8 project, we use a popup with a grid to host the content.

When this page contains a LongListSelector control, the Tap interaction to stop scrolling no longer works. Swiping up and down works as expected.

The issue can be reproduced very easily by starting with a new Databound app and adding this piece of code in the page constructor:

private Popup p;

p = new Popup();
Grid grid = new Grid();
grid.Width = Application.Current.Host.Content.ActualWidth;
grid.Height = Application.Current.Host.Content.ActualHeight;
p.Child = grid;
p.IsOpen = true;

Using this code you can make the LongListSelector scrolling but a Tap does no longer work to stop the scrolling.

Has anyone seen this issue and found a solution or might this be a known issue with the LongListSelector?

Answer 1

The invisible Grid that you're putting over the LongListSelector (actually the whole page) is capturing the tap event and because the popup is not part of the visual tree the event doesn't bubble as you're expecting.

The anomaly here is that you can actually interact with the LLS at all.

The real question here isn't why this happens but why you'd do this? Obviously your reproduction is very simple but it's to a point that makes no sense.

What are you ultimately trying to achieve?
There are almost certainly more appropriate alternative ways to achieve your end goal.