Recycling that Item Container

Scrolling Performance in WPF

Rudi Grobler — Thu, 22 May 2008 11:51:34 GMT

With the beta release of .NET 3.5 SP1, scrolling received some much needed performance increases! Lets

WPF 3.5 SP1 Feature: Non-live Scrolling

Vincent Sibal's Blog — Thu, 22 May 2008 17:58:49 GMT

So far for the new WPF 3.5 SP1 features, I've surveyed Item Container Recycling , Data Formatting , and

re: Recycling that Item Container

shunchen — Fri, 11 Jul 2008 08:39:05 GMT

Hi,

While i use the listview in WPF, I found a urgent question. I know that it has implemented the UI virtualization in listview, so it can throw away containers every time they go out of view. But i want to know what it mean exactly about "throw away". By my test, it seems the memory are always occupied, not released. For example, i add 1000+ items into listview, then it will take up a large number of memory while i scrolling. The most important is that the memory can't be released automatically, except closing the application.

What can i do about the issue?

Thanks

re: Recycling that Item Container

vinsibal — Fri, 11 Jul 2008 11:58:28 GMT

Virtualization from the VirtualizingStackPanel's point of view means that memory is allocated for the panel's item containers that are in view. When they go out of view they are "thrown away" meaning they will be set to be garbage collected (whenever that will be which is set by the garbage collector). I'm not exactly sure how you are testing the memory footprint of your app from what you are saying so I can't really make any conclusions from it. Also, it's a managed app so you only have so much control of the garbage collector. Do you also have item container recycling turned on? I just did a really quick and dirty test with an app that I'm current developing and added a ListView with 100 items and item container recycling turn on and off. With it off the memory footprint of my app was between 132MB - 135MB. When I turned it back on it was between 77MB - 84MB. So one thing that you can do and get for free is turn on item container recycling (if you haven't done so).

Also, if you do want to see the performance impact, try turning off virtualization and then try scrolling. I accidentally ran into this issue the other day as I forgot that when you add grouping, virtualization is automatically turned off. I had around 4000 items which is relatively not that many and my app was slowed down to a crawl.

re: Recycling that Item Container

Shunchen — Wed, 16 Jul 2008 13:02:24 GMT

Hi, vinsibal

Thanks for your help firstly. I tried that new property VirtualizationMode="Recycling" in SP1. The result is perfect that the memory usage is cut.

However, i found another urgent issue while i updated to SP1. If VirtualizationMode is set with "Recycling", I tried to clear the collection (which binding to the listview's itemssource) and fill it with new items. Then it will throw exception if invoking the ScrollIntoView() of listbox.

>> It can work well with .net 3.5(no sp1)

>> It can work well if VirtualizationMode isn't set with "Recycling"

>> It can work well if removing items in collection (which binding to itemssource) one by one instead of clearing it. I means that to call RemoveAt() instead of Clear() .

re: Recycling that Item Container

vinsibal — Thu, 17 Jul 2008 19:22:11 GMT

Thanks for all the information. I was able to repro exactly. After some investigation, we found this is a bug in the recycling code. It has been logged and will be addressed in our future release.

Right now it seems that the RemoveAt function is the easiest workaround right now but I will look into this a bit more to see if there is a more intuitive work around. Thanks again for your commetns!

cheat-sheet to some of the WPF 3.5 SP1 features..

Jaime Rodriguez — Fri, 15 Aug 2008 10:42:29 GMT

.NET 3.5 SP1 buzz peaked very early at the beta.  At the time I was immersed in Silverlight, so

re: Recycling that Item Container

Luke — Thu, 09 Jul 2009 10:27:03 GMT

Any news on when Virtualization support will be supported when grouping within the ListView is enabled?

re: Recycling that Item Container

vinsibal — Tue, 11 Aug 2009 15:44:46 GMT

Luke,

It is on the list of features for future releases but we do not have any solid dates for when that will be supported. In the meantime you can make use of the workaround that I have a link for here, http://blogs.msdn.com/vinsibal/archive/2008/06/12/grouping-and-virtualization.aspx.