如何:改善 TreeView 的效能
TreeView如果 包含許多專案,載入所需的時間量可能會造成使用者介面的重大延遲。 您可以將附加屬性設定 VirtualizingStackPanel.IsVirtualizing
為 true
來改善載入時間。 當使用者使用滑鼠滾輪或拖曳捲軸的拇指時 TreeView ,UI 可能也會變慢回應。 您可以將附加屬性設定 VirtualizingStackPanel.VirtualizationMode
為 VirtualizationMode.Recycling ,以改善 使用者捲動時的效能 TreeView 。
範例
描述
下列範例會建立 , TreeView 將 VirtualizingStackPanel.IsVirtualizing
附加屬性設定為 true,並將 VirtualizingStackPanel.VirtualizationMode
附加屬性設定為 VirtualizationMode.Recycling ,以優化其效能。
代碼
<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>
下列範例顯示上一個範例使用的資料。
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
{
level2Items ??= new ObservableCollection<string>();
return level2Items;
}
}
public ItemsForTreeView()
{
for (int i = 0; i < 10; ++i)
{
SecondLevelItems.Add("Second Level " + i.ToString());
}
}
}
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
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