Very slow grouping

Question

Hello!

I have a problem with grouping in "ObservableCollection -> CollectionViewSource -> ListView" scenario.

In a couple of words: Changes in grouping and is too slow! Moreover, scrolling in the grouped ListView is very slow as well.

Here's an example (based on CollectionViewSource SDK sample - July CTP):

FILE: Data.cs - just a collection (of 1000 items) of some domain specific objects (hotels in this case)

using System.Windows;

using System.Collections.ObjectModel;

 

namespace SDKSample

{

    public class Hotel

    {

        private string name;

        private string city;

        private string rating;

 

        public string Name

        {

            get { return name; }

            set { name = value; }

        }

 

        public string City

        {

            get { return city; }

            set { city = value; }

        }

 

        public string Rating

        {

            get { return rating; }

            set { rating = value; }

        }

 

        public Hotel(string name, string city, string rating)

        {

            this.name = name;

            this.city = city;

            this.rating = rating;

        }

    }

 

    public class Hotels : ObservableCollection<Hotel>

    {

        public Hotels()

        {

            string[] cities = { "Moscow", "New York", "Paris" };

            string[] ratings = { "Bad", "Good", "The best!" };

 

            System.Random rnd = new System.Random();

 

            for (int i = 0; i < 1000; i++)

            {

                string city = cities[rnd.Next(cities.Length)];

                string rating = ratings[rnd.Next(ratings.Length)];

 

                Add(new Hotel("Hotel#" + i, city, rating));

            }

        }

    }

}

FILE: Window1.xaml  - CollectionViewSource, grouping buttons and the ListView in GridView mode

<Window x:Class="SDKSample.Window1"

  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

  xmlns:src="clr-namespace:SDKSample"

  xmlns:dat="clr-namespace:System.Windows.Data;assembly=PresentationFramework"

  Title="Slow grouping sample">

 

  <Window.Resources>

 

    <src:Hotels x:Key="hotels"/>

 

    <CollectionViewSource Source="{StaticResource hotels}" x:Key="cvs">

      <CollectionViewSource.GroupDescriptions>

        <dat:PropertyGroupDescription PropertyName="City"/>

      </CollectionViewSource.GroupDescriptions>

    </CollectionViewSource>

 

  </Window.Resources>

  <DockPanel>

    <StackPanel Orientation="Horizontal" DockPanel.Dock="Top" Margin="10,10,10,10">

        <TextBlock Text="Group by: "/>

        <RadioButton Name="City" IsChecked="True" Checked="ChangeGrouping" Content="City"/>

        <RadioButton Name="Rating" Checked="ChangeGrouping" Content="Rating"/>

        <RadioButton Name="None" Checked="ChangeGrouping" Content="No grouping"/>

    </StackPanel>

 

    <ListView ItemsSource="{Binding Source={StaticResource cvs}}"

              VirtualizingStackPanel.IsVirtualizing="True"

              Name="lv">

      <ListView.GroupStyle>

        <x:Static Member="GroupStyle.Default"/>

      </ListView.GroupStyle>

 

      <ListView.View>

        <GridView>

          <GridViewColumn Header="Hotel" DisplayMemberBinding="{Binding Path=Name}"/>

          <GridViewColumn Header="City" DisplayMemberBinding="{Binding Path=City}"/>

          <GridViewColumn Header="Rating" DisplayMemberBinding="{Binding Path=Rating}"/>

        </GridView>

      </ListView.View>

 

    </ListView>

 

  </DockPanel>

</Window>

FILE Window1.xaml.cs - grouping code

using System.Windows;

using System.Collections.ObjectModel;

using System.Windows.Data;

using System.ComponentModel;

using System.Windows.Controls;

 

namespace SDKSample

{

    public partial class Window1 : Window

    {

        private CollectionViewSource dataView;

 

        public Window1()

        {

            InitializeComponent();

            dataView = (CollectionViewSource)(this.Resources["cvs"]);

        }

 

        private void ChangeGrouping(object sender, RoutedEventArgs args)

        {

            if (dataView == null)

                return;

 

            RadioButton buttonClicked = args.OriginalSource as RadioButton;

            string groupBy = buttonClicked.Name;

 

            // Avoid unnecessary updates

            if (dataView.GroupDescriptions.Count != 1 ||

                ((PropertyGroupDescription)dataView.GroupDescriptions[0]).PropertyName !=

                   groupBy)

            {

                using (dataView.DeferRefresh())

                {

                    dataView.GroupDescriptions.Clear();

                    if (groupBy != "None")

                    {

                        PropertyGroupDescription groupDescription =

                            new PropertyGroupDescription();

                        groupDescription.PropertyName = groupBy;

                        dataView.GroupDescriptions.Add(groupDescription);

                    }

                }

            }

        }

    }

}

That's all.

Test #1

Try to change grouping mode (for example, from "City" to "Rating"). It takes about 5 seconds (!) on my P4 2.8Gz 2Gb RAM machine (.NET 3 July CTP)!

Test #2

When the ListView is grouped by City or Rating try to scroll down it using Page Down key. Each page takes about 2 seconds!

Now, change grouping to "No grouping" and try to scroll again - this time it scrolls fast. So, a grouping affects scrolling somehow.

Question

Why grouping and scrolling is so slow in this particular scenario? Is there any way to speed it up?

Thanks in advance!

Answer 1

The case you are encountering is a particularity of the ItemsControl/ListBox/ListView controls...

Whenever a "GroupStyle" is set on the control, the panel that layouts the items changes from VirtualizingStackPanel to StackPanel (this is a hack in MS code)...

Since UI Virtualization goes off, all of your 1000 items gets "realized" and this is the reason for the 5 seconds loading time... At the same time, when you scroll, the StackPanel have to calculate the new position of your 1000 items, hence the 2 seconds...

Therefore, performance and grouping are not pairing togheter well in those controls... And there is currently no alternative to this.

Answer 2

Hi Marcus,

Thanks a lot for reply. I got an idea.

I'd like to know - is the current behavior is "by design" and won't change OR it's just a bug/not implemented feature?

Grouping is an essential feature of ListBox/ListView controls.

Thanks

Answer 3

Just found this bug on Microsoft Connect:

https://connect.microsoft.com/feedback/ViewFeedback.aspx?FeedbackID=123998&SiteID=212

Too bad, it could be a showstopper in my project.

Answer 4

Marc,  any news on when Virtualization support will be supported when grouping within the ListView is enabled?  This issue has been around for a long time now and should have been fixed by now I would think.