Nasıl Yapılır: TreeView Performansını İyileştirme
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.
Örnek
Description
The following example creates a TreeView that sets VirtualizingStackPanel.IsVirtualizing to true and VirtualizingStackPanel.VirtualizationMode 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>
<TreeView Height="200"
ItemsSource="{Binding Source={StaticResource dataItems}}"
VirtualizingStackPanel.IsVirtualizing="True"
VirtualizingStackPanel.VirtualizationMode="Recycling">
<TreeView.ItemContainerStyle>
<!--Expand each TreeViewItem in the first level and
set its foreground to Green.-->
<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());
}
}
}