How to: Improve the Performance of a TreeView

If a TreeView contains many items, the amount of time it takes to load may cause a significant delay in the user interface. You can improve the load time by setting the VirtualizingStackPanel.IsVirtualizing attached property to true. The UI might also be slow to react when a user scrolls the TreeView by using the mouse wheel or dragging the thumb of a scrollbar. You can improve the performance of the TreeView when the user scrolls by setting the VirtualizingStackPanel.VirtualizationMode attached property to Recycling.

Example

Description

The following example creates a TreeView that sets VirtualizingStackPanel.IsVirtualizing to true and VirtualizingStackPanelVirtualizationMode to Recycling to optimize its performance.

Code

<StackPanel>
  <StackPanel.Resources>
    <src:TreeViewData x:Key="dataItems"/>


    <HierarchicalDataTemplate DataType="{x:Type src:ItemsForTreeView}"
                              ItemsSource="{Binding Path=SecondLevelItems}">

      <!--Display the TopLevelName property in the first level.-->
      <TextBlock Text="{Binding Path=TopLevelName}"/>

      <!--Display each string in the SecondLevelItems property in
          the second level.-->
      <HierarchicalDataTemplate.ItemTemplate>
        <DataTemplate>
          <TextBlock Text="{Binding}"/>
        </DataTemplate>
      </HierarchicalDataTemplate.ItemTemplate>

      <!--Set the foreground of the items in the second level
          to Navy.-->
      <HierarchicalDataTemplate.ItemContainerStyle>
        <Style TargetType="TreeViewItem">
          <Setter Property="Foreground" Value="Navy"/>
        </Style>
      </HierarchicalDataTemplate.ItemContainerStyle>
    </HierarchicalDataTemplate>
  </StackPanel.Resources>

  <!--Set VirtualizingStackPanel.IsVirtualizing to true and
      VirtualizingStackPanel.VirtualizationMode to Recycling
      to improve scrolling performance in the TreeView.-->
  <TreeView Height="200" ItemsSource="{Binding Source={StaticResource dataItems}}"
            VirtualizingStackPanel.IsVirtualizing="True"
            VirtualizingStackPanel.VirtualizationMode="Recycling">

    <!--Expand each TreeViewItem in the first level and 
        set its foreground to Green.-->
    <TreeView.ItemContainerStyle>
      <Style TargetType="TreeViewItem">
        <Setter Property="IsExpanded" Value="True"/>
        <Setter Property="Foreground" Value="Green"/>
      </Style>
    </TreeView.ItemContainerStyle>
  </TreeView>
</StackPanel>

The following example shows the data that the previous example uses.

Public Class TreeViewData
    Inherits ObservableCollection(Of ItemsForTreeView)

    Public Sub New()
        For i As Integer = 0 To 99
            Dim item As New ItemsForTreeView()
            item.TopLevelName = "item " & i.ToString()
            Add(item)
        Next 
    End Sub 
End Class 


Public Class ItemsForTreeView
    Private _TopLevelName As String 
    Public Property TopLevelName() As String 
        Get 
            Return _TopLevelName
        End Get 
        Set(ByVal value As String)
            _TopLevelName = value
        End Set 
    End Property 
    Private level2Items As ObservableCollection(Of String)

    Public ReadOnly Property SecondLevelItems() As ObservableCollection(Of String)
        Get 
            If level2Items Is Nothing Then
                level2Items = New ObservableCollection(Of String)()
            End If 
            Return level2Items
        End Get 
    End Property 

    Public Sub New()
        For i As Integer = 0 To 9
            SecondLevelItems.Add("Second Level " & i.ToString())
        Next 
    End Sub 
End Class

public class TreeViewData : ObservableCollection<ItemsForTreeView>
{

    public TreeViewData()
    {
        for (int i = 0; i < 100; ++i)
        {
            ItemsForTreeView item = new ItemsForTreeView();
            item.TopLevelName = "item " + i.ToString();
            Add(item);
        }
    }
}


public class ItemsForTreeView
{
    public string TopLevelName { get; set; }
    private ObservableCollection<string> level2Items;

    public ObservableCollection<string> SecondLevelItems
    {
        get 
        {
            if (level2Items == null)
            {
                level2Items = new ObservableCollection<string>();
            }
            return level2Items;
        }
    }

    public ItemsForTreeView()
    {
        for (int i = 0; i < 10; ++i)
        {
            SecondLevelItems.Add("Second Level " + i.ToString());
        }
    }
}

See Also

Concepts

Optimizing Performance: Controls

Change History