Variable Size Items with LogicalScrolling / Virtualized StackPanel

[danwalmsley]

You can repro with the virtualisation demo.

1. Change the item template so each item is an expander.
2. add a 200x200 grid inside the expander.
3. add a load of items so that scrolling is needed.
4. expand an item near bottom of list so its partially obscured.
5. scroll down, it should crash trying to recycle items when it shouldn't.

I think there are a couple of things:

logical scrolling is assuming fix sized items,
virtualized stack panel is calculating the number of items to recycle bases on the logical scroll size (fixed)

[grokys]

I've just tried this repro in the VirtualizationDemo project and I can't reproduce. What am I missing?

[grokys]

Also a stacktrace, or at least the type of the exception thrown would be useful.

[danwalmsley]

not able to repro the crash yet, but here you can see symptoms that point to the same issue:

repro here:

1. the last item doesn't adjust the scrollbar enough when the item is expanded.

2. scrolling back up the list recycles the container causing different items to be expanded.

I suspect #2 will be hard to fix if not impossible :)

[danwalmsley]

It has been determined at least that the issue with the expanded item moving up is that this is caused by recycling.

Will try to do a PR for a VirtualizationMode="Simple" and VirtualizationMode="Recycling"

[danwalmsley]

Ok I realised its pointless as you still loose the state of the items.

The real solution is to bind the state you need to persist.

I was seeing some crashing so I will leave open until I confirm that.