Eu tenho uma barra de rolagem vertical personalizada que exibe marcadores para itens selecionados em um DataGrid.

O problema que estou enfrentando é que, quando há um grande número de itens (por exemplo, de 5000 a 50000), ocorre um atraso durante a renderização dos marcadores.

Com o código a seguir, ele processa basicamente de acordo com o índice de itens selecionados, número de itens e altura da faixa. Obviamente, isso é ineficiente e estou procurando outras soluções.

Esta é minha barra de rolagem vertical personalizada

<helpers:MarkerPositionConverter x:Key="MarkerPositionConverter"/>

<ControlTemplate x:Key="VerticalScrollBar" TargetType="{x:Type ScrollBar}">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition MaxHeight="18" />
            <RowDefinition Height="0.00001*" />
            <RowDefinition MaxHeight="18" />
        </Grid.RowDefinitions>
        <Border Grid.RowSpan="3"
                        CornerRadius="2"
                        Background="#F0F0F0" />
        <RepeatButton Grid.Row="0"
                              Style="{StaticResource ScrollBarLineButton}"
                              Height="18"
                              Command="ScrollBar.LineUpCommand"
                              Content="M 0 4 L 8 4 L 4 0 Z" />
        <!--START-->
        <ItemsControl VerticalAlignment="Stretch"  x:Name="ItemsSelected"
                                   ItemsSource="{Binding ElementName=GenericDataGrid, Path=SelectedItems}">
            <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <Rectangle Fill="SlateGray" Width="9" Height="4">
                        <Rectangle.RenderTransform>
                            <TranslateTransform>
                                <TranslateTransform.Y>
                                    <MultiBinding Converter="{StaticResource MarkerPositionConverter}" FallbackValue="-1000">
                                        <Binding/>
                                        <Binding RelativeSource="{RelativeSource AncestorType={x:Type DataGrid}}" />
                                        <Binding Path="ActualHeight" ElementName="ItemsSelected"/>
                                        <Binding Path="Items.Count" ElementName="GenericDataGrid"/>
                                    </MultiBinding>
                                </TranslateTransform.Y>
                            </TranslateTransform>
                        </Rectangle.RenderTransform>
                    </Rectangle>
                </DataTemplate>
            </ItemsControl.ItemTemplate>
            <ItemsControl.ItemsPanel>
                <ItemsPanelTemplate>
                    <Canvas ClipToBounds="True"/>
                </ItemsPanelTemplate>
            </ItemsControl.ItemsPanel>
        </ItemsControl>
        <!--END-->
        <Track x:Name="PART_Track" Grid.Row="1" IsDirectionReversed="true">
            <Track.DecreaseRepeatButton>
                <RepeatButton Style="{StaticResource ScrollBarPageButton}"
                                      Command="ScrollBar.PageUpCommand" />
            </Track.DecreaseRepeatButton>
            <Track.Thumb>
                <Thumb Style="{StaticResource ScrollBarThumb}" Margin="1,0,1,0">
                    <Thumb.BorderBrush>
                        <LinearGradientBrush StartPoint="0,0" EndPoint="1,0">
                            <LinearGradientBrush.GradientStops>
                                <GradientStopCollection>
                                    <GradientStop Color="{DynamicResource BorderLightColor}" Offset="0.0" />
                                    <GradientStop Color="{DynamicResource BorderDarkColor}" Offset="1.0" />
                                &l,t;/GradientStopCollection>
                            </LinearGradientBrush.GradientStops>
                        </LinearGradientBrush>
                    </Thumb.BorderBrush>
                    <Thumb.Background>
                        <LinearGradientBrush StartPoint="0,0"
                                 EndPoint="1,0">
                            <LinearGradientBrush.GradientStops>
                                <GradientStopCollection>
                                    <GradientStop Color="{DynamicResource ControlLightColor}" Offset="0.0" />
                                    <GradientStop Color="{DynamicResource ControlMediumColor}" Offset="1.0" />
                                </GradientStopCollection>
                            </LinearGradientBrush.GradientStops>
                        </LinearGradientBrush>
                    </Thumb.Background>
                </Thumb>
            </Track.Thumb>
            <Track.IncreaseRepeatButton>
                <RepeatButton Style="{StaticResource ScrollBarPageButton}" Command="ScrollBar.PageDownCommand" />
            </Track.IncreaseRepeatButton>
        </Track>
        <RepeatButton Grid.Row="3" Style="{StaticResource ScrollBarLineButton}" Height="18" Command="ScrollBar.LineDownCommand" Content="M 0 0 L 4 4 L 8 0 Z" />
    </Grid>
</ControlTemplate>

Este é o meu conversor que transforma a posição Y e escala conforme a altura do DataGrid muda.

public class MarkerPositionConverter: IMultiValueConverter
{
    //Performs the index to translate conversion
    public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        try
        {
            //calculated the transform values based on the following
            object o = (object)values[0];
            DataGrid dg = (DataGrid)values[1];
            double itemIndex = dg.Items.IndexOf(o);
            double trackHeight = (double)values[2];
            int itemCount = (int)values[3];
            double translateDelta = trackHeight / itemCount;
            return itemIndex * translateDelta;
        }
        catch (Exception ex)
        {
            Console.WriteLine("MarkerPositionConverter error : " + ex.Message);
            return false;
        }
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

[EDITAR] Eu tentei criar uma classe separada para uma tela de marcador, para uso com os ObservableCollection. Observe que, no momento, isso não funciona.

XAML ainda é o mesmo de ontem:

<helpers:MarkerCollectionCanvas 
         x:Name="SearchMarkerCanvas" 
         Grid.Row="1" 
         Grid="{Binding RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}"
         MarkerCollection="{Binding Source={x:Static helpers:MyClass.Instance}, Path=SearchMarkers}"/>

A classe Canvas, ObservableCollection foi alterada para usar o objeto em vez de double, existe um console.writeline em MarkerCollectionCanvas_CollectionChanged que nunca é chamado:

class MarkerCollectionCanvas : Canvas
{
    public DataGrid Grid
    {
        get { return (DataGrid)GetValue(GridProperty); }
        set { SetValue(GridProperty, value); }
    }

    public static readonly DependencyProperty GridProperty =
        DependencyProperty.Register("Grid", typeof(DataGrid), typeof(MarkerCollectionCanvas), new PropertyMetadata(null));

    public ObservableCollection<object> MarkerCollection
    {
        get { return (ObservableCollection<object>)GetValue(MarkerCollectionProperty); }
        set { SetValue(MarkerCollectionProperty, value); }
    }

    public static readonly DependencyProperty MarkerCollectionProperty =
        DependencyProperty.Register("MarkerCollection", typeof(ObservableCollection<object>), typeof(MarkerCollectionCanvas), new PropertyMetadata(null, OnCollectionChanged));

    private static void OnCollectionChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        MarkerCollectionCanvas canvas = d as MarkerCollectionCanvas;

        if (e.NewValue != null)
        {
            (e.NewValue as ObservableCollection<object>).CollectionChanged += canvas.MarkerCollectionCanvas_CollectionChanged;
        }
        if (e.OldValue != null)
        {
            (e.NewValue as ObservableCollection<object>).CollectionChanged -= canvas.MarkerCollectionCanvas_CollectionChanged;
        }
    }

    void MarkerCollectionCanvas_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        Console.WriteLine("InvalidateVisual");
        InvalidateVisual();
    }

    public Brush MarkerBrush
    {
        get { return (Brush)GetValue(MarkerBrushProperty); }
        set { SetValue(MarkerBrushProperty, value); }
    }

    public static readonly DependencyProperty MarkerBrushProperty =
        DependencyProperty.Register("MarkerBrush", typeof(Brush), typeof(MarkerCollectionCanvas), new PropertyMetadata(Brushes.DarkOrange));

    protected override void OnRender(System.Windows.Media.DrawingContext dc)
    {
        base.OnRender(dc);

        if (Grid == null || MarkerCollection == null)
            return;

        //Get all items
        object[] items = new object[Grid.Items.Count];
        Grid.Items.CopyTo(items, 0);

        //Get all selected items
        object[] selection = new object[MarkerCollection.Count];
        MarkerCollection.CopyTo(selection, 0);

        Dictionary<object, int> indexes = new Dictionary<object, int>();

        for (int i = 0; i < selection.Length; i++)
        {
            indexes.Add(selection[i], 0);
        }

        int itemCounter = 0;
        for (int i = 0; i < items.Length; i++)
        {
            object item = items[i];
            if (indexes.ContainsKey(item))
            {
                indexes[item] = i;
                itemCounter++;
            }
            if (itemCounter >= selection.Length)
                break;
        }

        double translateDelta = ActualHeight / (double)items.Length;
        double width = ActualWidth;
        double height = Math.Max(translateDelta, 4);
        Brush dBrush = MarkerBrush;
        double previous = 0;

        IEnumerable<int> sortedIndex = indexes.Values.OrderBy(v => v);

        foreach (int itemIndex in sortedIndex)
        {
            double top = itemIndex * translateDelta;
            if (top < previous)
                continue;

            dc.DrawRectangle(dBrush, null, new Rect(0, top, width, height));
            previous = (top + height) - 1;
        }
    }
}

Esta é minha classe singleton com SearchMarkers:

public class MyClass : INotifyPropertyChanged
{
    public static ObservableCollection<object> m_searchMarkers = new ObservableCollection<object>();
    public ObservableCollection<object> SearchMarkers
    {
        get
        {
            return m_searchMarkers;
        }
        set
        {
            m_searchMarkers = value;
            NotifyPropertyChanged();
        }
    }

    private static MyClass m_Instance;
    public static MyClass Instance
    {
        get
        {
            if (m_Instance == null)
            {
                m_Instance = new MyClass();
            }

            return m_Instance;
        }
    }

    private MyClass()
    {
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

E este é um texto alterado na caixa de texto. É aqui que o ObservableCollection SearchMarkers é preenchido.

public class FindTextChangedBehavior : Behavior<TextBox>
{
    protected override void OnAttached()
    {
        base.OnAttached();
        AssociatedObject.TextChanged += OnTextChanged;
    }

    protected override void OnDetaching()
    {
        AssociatedObject.TextChanged -= OnTextChanged;
        base.OnDetaching();
    }

    private void OnTextChanged(object sender, TextChangedEventArgs args)
    {
        var textBox = (sender as TextBox);
        if (textBox != null)
        {
            DataGrid dg = DataGridObject as DataGrid;
            string searchValue = textBox.Text;

            if (dg.Items.Count > 0)
            {
                var columnBoundProperties = new List<KeyValuePair<int, string>>();

                IEnumerable<DataGridColumn> visibleColumns = dg.Columns.Where(c => c.Visibility == System.Windows.Visibility.Visible);

                foreach (var col in visibleColumns)
                {
                    if (col is DataGridTextColumn)
                    {
                        var binding = (col as DataGridBoundColumn).Binding as Binding;
                        columnBoundProperties.Add(new KeyValuePair<int, string>(col.DisplayIndex, binding.Path.Path));
                    }
                    else if (col is DataGridComboBoxColumn)
                    {
                        DataGridComboBoxColumn dgcbc = (DataGridComboBoxColumn)col;
                        var binding = dgcbc.SelectedItemBinding as Binding;
                        columnBoundProperties.Add(new KeyValuePair<int, string>(col.DisplayIndex, binding.Path.Path));
                    }
                }

                Type itemType = dg.Items[0].GetType();
                if (columnBoundProperties.Count > 0)
                {
                    ObservableCollection<Object> tempItems = new ObservableCollection<Object>();
                    var itemsSource = dg.Items as IEnumerable;
                    Task.Factory.StartNew(() =>
                    {
                        ClassPropTextSearch.init(itemType, columnBoundProperties);
                        if (itemsSource != null)
                        {
                            foreach (object o in itemsSource)
                            {
                                if (ClassPropTextSearch.Match(o, searchValue))
                                {
                                    tempItems.Add(o);
                                }
                            }
                        }
                    })
                    .ContinueWith(t =>
                    {
                        Application.Current.Dispatcher.Invoke(new Action(() => MyClass.Instance.SearchMarkers = tempItems));
                    });
                }
            }
        }
    }

    public static readonly DependencyProperty DataGridObjectProperty =
        DependencyProperty.RegisterAttached("DataGridObject", typeof(DataGrid), typeof(FindTextChangedBehavior), new UIPropertyMetadata(null));

    public object DataGridObject
    {
        get { return (object)GetValue(DataGridObjectProperty); }
        set { SetValue(DataGridObjectProperty, value); }
    }
}