Cannot change the VirtualizationMode attached property on an ItemsControl after Measure is called on the ItemsHost panel

Question

When i try to set VirtualizationMode on my ListView to Recycling I get the error from the title:

Cannot change the VirtualizationMode attached property on an ItemsControl after Measure is called on the ItemsHost panel.

I am trying to set the attached property programmatically but when I try to define the VirtualizationMode in XAML designer throws the same error from the title. Anyone had similar problems like this?

My view in XAML is:

And i try to set the VirtualizationMode here:

public void SetUIVirtualizationOptions()
{
    listView.SetValue(VirtualizingStackPanel.IsVirtualizingProperty, IsUIVirtualization);
    listView.SetValue(ScrollViewer.IsDeferredScrollingEnabledProperty, IsDeferredScrolling);

    if(ContainerRecyclingType == "Recycling")
        listView.SetValue(VirtualizingStackPanel.VirtualizationModeProperty, VirtualizationMode.Recycling);
    else
        listView.SetValue(VirtualizingStackPanel.VirtualizationModeProperty, VirtualizationMode.Standard);


    if (ScrollUnitType == "Item")
        listView.SetValue(VirtualizingPanel.ScrollUnitProperty, ScrollUnit.Item);
    else
        listView.SetValue(VirtualizingPanel.ScrollUnitProperty, ScrollUnit.Pixel);
}

Edit: My Window code behind where i pass the listview to viewmodel is:

    {
        public MainWindow()
        {
            InitializeComponent();
            DataContext = new MainWindowViewModel(lvItems);
        }
    }

And the viewmodel part of the code (minus getters and setters for less space taken):

public class MainWindowViewModel : BindableBase
    {
        #region private fields
        private ListView listView;
        private bool isUIVirtualization;
        private bool isDeferredScrolling;
        private string containerRecyclingType;
        private string scrollUnitType;
        private int numberOfItems;
        private int fetchDelay;
        private string collectionType;
        private int pageSize;
        private int pageTimeout;
        private string memoryUsage;
        private DemoItemProvider itemsProvider;
        #endregion

        #region commands
        public RelayCommand CollectionTypeChangeCommand { get; set; }
        public RelayCommand RefreshCommand { get; set; }
        public RelayCommand ContainerRecyclingTypeChangeCommand { get; set; }
        public RelayCommand ScrollUnitTypeChangeCommand { get; set; }
        #endregion

        public MainWindowViewModel(ListView lvItems)
        {
            this.listView = lvItems;
            PageSize = 100;
            PageTimeout = 30;
            NumberOfItems = 1000000;
            FetchDelay = 1000;

            CollectionTypeChangeCommand = new RelayCommand(CollectionTypeChangeFunc);
            RefreshCommand = new RelayCommand(RefreshFunc);
            ContainerRecyclingTypeChangeCommand = new RelayCommand(ContainerRecyclingTypeChangeFunc);
            ScrollUnitTypeChangeCommand = new RelayCommand(ScrollUnitTypeChangeFunc);

            // use a timer to periodically update the memory usage
            DispatcherTimer timer = new DispatcherTimer();
            timer.Interval = new TimeSpan(0, 0, 1);
            timer.Tick += timer_Tick;
            timer.Start();
        }

        private void timer_Tick(object sender, EventArgs e)
        {
            MemoryUsage = string.Format("{0:0.00} MB", GC.GetTotalMemory(true) / 1024.0 / 1024.0);
        }

        #region command methods
        public void CollectionTypeChangeFunc(string type)
        {
            CollectionType = type;
        }

        public void RefreshFunc()
        {
            SetUIVirtualizationOptions();
            itemsProvider = new DemoItemProvider(NumberOfItems, FetchDelay);


            if (collectionType == "List")
            {
                listView.ItemsSource = new List(itemsProvider.FetchRange(0, itemsProvider.FetchCount()));
            }
            else if (collectionType == "VirtualizingList")
            {
                listView.ItemsSource = new VirtualizingCollection(itemsProvider, pageSize);
            }
            else if (collectionType == "AsyncVirtualizingList")
            {
                listView.ItemsSource = new AsyncVirtualizingCollection(itemsProvider, pageSize, pageTimeout * 1000);
            }
        }

        public void ContainerRecyclingTypeChangeFunc(string type)
        {
            ContainerRecyclingType = type;
        }

        public void ScrollUnitTypeChangeFunc(string type)
        {
            ScrollUnitType = type;
        }

        public void SetUIVirtualizationOptions()
        {
            listView.SetValue(VirtualizingStackPanel.IsVirtualizingProperty, IsUIVirtualization);
            listView.SetValue(ScrollViewer.IsDeferredScrollingEnabledProperty, IsDeferredScrolling);

            if(ContainerRecyclingType == "Recycling")
                listView.SetValue(VirtualizingStackPanel.VirtualizationModeProperty, VirtualizationMode.Recycling);
            else
                listView.SetValue(VirtualizingStackPanel.VirtualizationModeProperty, VirtualizationMode.Standard);


            if (ScrollUnitType == "Item")
                listView.SetValue(VirtualizingPanel.ScrollUnitProperty, ScrollUnit.Item);
            else
                listView.SetValue(VirtualizingPanel.ScrollUnitProperty, ScrollUnit.Pixel);
        }
        #endregion
    }

Corentin Pane · Accepted Answer

The code source for VirtualizingStackPanel indicates that this property can only be set before initialization of the panel:

/// 
///     Attached property for use on the ItemsControl that is the host for the items being 
///     presented by this panel. Use this property to modify the virtualization mode.
/// 
///     Note that this property can only be set before the panel has been initialized 
/// 
public static readonly DependencyProperty VirtualizationModeProperty = 
    DependencyProperty.RegisterAttached("VirtualizationMode", typeof(VirtualizationMode), typeof(VirtualizingStackPanel),
        new FrameworkPropertyMetadata(VirtualizationMode.Standard));

You can indeed check this behavior later in the file:

//
// Set up info on first measure
//
if (HasMeasured)
{
    VirtualizationMode oldVirtualizationMode = InRecyclingMode ? VirtualizationMode.Recycling : VirtualizationMode.Standard;
    if (oldVirtualizationMode != virtualizationMode)
    {
        throw new InvalidOperationException(SR.Get(SRID.CantSwitchVirtualizationModePostMeasure));
    }
}
else
{
    HasMeasured = true;
}

and there is no way (according to source code) to set this HasMeasured property back to False unless you destroy and recreate the ListView.

Cannot change the VirtualizationMode attached property on an ItemsControl after Measure is called on the ItemsHost panel

Answers (2)

Related Questions