當覆蓋ScrollViewer的默認控制模板時，VirtualizingStackPanel停止工作

Question

我有一個列表框，其中有很多渲染費用很高的項目。然而，VirtualizingStackPanel僅通過渲染可見項目來處理。我想覆蓋ScrollViewer的控件模板，因爲默認的模板在水平和垂直滾動條之間有灰色矩形。我剛剛複製了微軟提供的那個（ScrollViewer ControlTemplate Example），它沒有灰色的矩形問題。

但是，此控件模板通過給予VirtualizingStackPanel無窮高度來禁用虛擬化。這意味着VirtualizingStackPanel將渲染所有項目，因爲它認爲所有項目都可見。

在下面的演示代碼中，我在列表框中顯示10000個項目。我通過比較運行ScrollViewer風格和沒有它來驗證問題。隨着演示運行速度非常緩慢，調整大小需要幾秒鐘。沒有風格，它非常快。 I輸出有關VirtualizingStackPanel一些信息，以證明我的觀點：

沒有的ScrollViewer樣式（註釋掉XAML的樣式）：

ViewportHeight：8
ExtentHeight：10000
的ActualHeight：245
IsVirtualizing：真
VirtualizationMode：標準

隨着ScrollViewer中的風格：

ViewportHeight：0
ExtentHeight：0
的ActualHeight：272766.666666707
IsVirtualizing：真
VirtualizationMode：標準

任何想法如何編寫控件模板的ScrollViewer中是不與虛擬化混亂？

XAML：

<Window x:Class="VirtualTest.Window1" 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    Title="Window1" Height="300" Width="300"> 

    <Window.Resources> 

     <Style x:Key="{x:Type ScrollViewer}" TargetType="{x:Type ScrollViewer}"> 
      <Setter Property="OverridesDefaultStyle" Value="true" /> 
      <Setter Property="Template"> 
       <Setter.Value> 
        <ControlTemplate TargetType="{x:Type ScrollViewer}"> 
         <Grid> 
          <Grid.ColumnDefinitions> 
           <ColumnDefinition /> 
           <ColumnDefinition Width="Auto" /> 
          </Grid.ColumnDefinitions> 
          <Grid.RowDefinitions> 
           <RowDefinition /> 
           <RowDefinition Height="Auto" /> 
          </Grid.RowDefinitions> 
          <ScrollContentPresenter Grid.Row="0" Grid.Column="0" /> 
          <ScrollBar 
           Name="PART_VerticalScrollBar" 
           Grid.Row="0" Grid.Column="1" 
           Value="{TemplateBinding VerticalOffset}" 
           Maximum="{TemplateBinding ScrollableHeight}" 
           ViewportSize="{TemplateBinding ViewportHeight}" 
           Visibility="{TemplateBinding ComputedVerticalScrollBarVisibility}" /> 
          <ScrollBar 
           Name="PART_HorizontalScrollBar" 
           Orientation="Horizontal" 
           Grid.Row="1" Grid.Column="0" 
           Value="{TemplateBinding HorizontalOffset}" 
           Maximum="{TemplateBinding ScrollableWidth}" 
           ViewportSize="{TemplateBinding ViewportWidth}" 
           Visibility="{TemplateBinding ComputedHorizontalScrollBarVisibility}" /> 
         </Grid> 
        </ControlTemplate> 
       </Setter.Value> 
      </Setter> 
     </Style> 

    </Window.Resources> 

    <Grid> 
     <ListBox 
      ItemsSource="{Binding Numbers}" 
      ScrollViewer.ScrollChanged="ListBox_ScrollChanged" 
      Background="Orange"> 
      <ListBox.ItemTemplate> 
       <DataTemplate> 
        <Border BorderBrush="Red" BorderThickness="2" Margin="5"> 
         <TextBlock Text="{Binding .}" Width="400"/> 
        </Border> 
       </DataTemplate> 
      </ListBox.ItemTemplate> 
     </ListBox> 

    </Grid> 
</Window> 

後面的代碼：

using System; 
using System.Collections.Generic; 
using System.Diagnostics; 
using System.Windows; 
using System.Windows.Controls; 
using System.Windows.Media; 

namespace VirtualTest 
{ 
    public partial class Window1 : Window 
    { 
     public Window1() 
     { 
      InitializeComponent(); 

      DataContext = this; 
     } 

     public IEnumerable<double> Numbers 
     { 
      get 
      { 
       for (int i = 0; i < 10000; i++) 
       { 
        yield return i; 
       } 
      } 
     } 

     private void ListBox_ScrollChanged(object sender, ScrollChangedEventArgs e) 
     { 
      ListBox listBox = sender as ListBox; 
      VirtualizingStackPanel virtualizingStackPanel = FindVirtualizingStackPanel(listBox);        
      Debug.WriteLine("ViewportHeight: " + virtualizingStackPanel.ViewportHeight); 
      Debug.WriteLine("ExtentHeight: " + virtualizingStackPanel.ExtentHeight); 
      Debug.WriteLine("ActualHeight: " + virtualizingStackPanel.ActualHeight); 
      Debug.WriteLine("IsVirtualizing: " + VirtualizingStackPanel.GetIsVirtualizing(virtualizingStackPanel)); 
      Debug.WriteLine("VirtualizationMode: " + VirtualizingStackPanel.GetVirtualizationMode(virtualizingStackPanel)); 
     } 

     private VirtualizingStackPanel FindVirtualizingStackPanel(Visual visual) 
     { 
      for (int i = 0; i < VisualTreeHelper.GetChildrenCount(visual); i++) 
      { 
       Visual child = VisualTreeHelper.GetChild(visual, i) as Visual; 

       if (child != null) 
       { 
        if (child is VirtualizingStackPanel) 
        { 
         return child as VirtualizingStackPanel; 
        } 

        VirtualizingStackPanel found = FindVirtualizingStackPanel(child); 
        if (found != null) 
        { 
         return found; 
        } 
       } 
      } 

      return null; 
     } 
    } 
} 

Answer 1

此的ScrollViewer樣式是從混合4複製它在輸出窗口看起來不錯

ViewportHeight：10
ExtentHeight：10000
Act ualHeight：308
IsVirtualizing：真
VirtualizationMode：標準

<Style TargetType="{x:Type ScrollViewer}"> 
    <Style.Triggers> 
     <Trigger Property="IsEnabled" Value="false"> 
      <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/> 
     </Trigger> 
    </Style.Triggers> 
    <Setter Property="Template" Value="{DynamicResource ScrollViewerControlTemplate1}"/> 
</Style> 
<ControlTemplate x:Key="ScrollViewerControlTemplate1" TargetType="{x:Type ScrollViewer}"> 
    <Grid x:Name="Grid" Background="{TemplateBinding Background}"> 
     <Grid.ColumnDefinitions> 
      <ColumnDefinition Width="*"/> 
      <ColumnDefinition Width="Auto"/> 
     </Grid.ColumnDefinitions> 
     <Grid.RowDefinitions> 
      <RowDefinition Height="*"/> 
      <RowDefinition Height="Auto"/> 
     </Grid.RowDefinitions> 
     <Rectangle x:Name="Corner" Grid.Column="1" Fill="{DynamicResource {x:Static SystemColors.ControlBrushKey}}" Grid.Row="1"/> 
     <ScrollContentPresenter x:Name="PART_ScrollContentPresenter" CanContentScroll="{TemplateBinding CanContentScroll}" CanHorizontallyScroll="False" CanVerticallyScroll="False" ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" Grid.Column="0" Margin="{TemplateBinding Padding}" Grid.Row="0"/> 
     <ScrollBar x:Name="PART_VerticalScrollBar" AutomationProperties.AutomationId="VerticalScrollBar" Cursor="Arrow" Grid.Column="1" Maximum="{TemplateBinding ScrollableHeight}" Minimum="0" Grid.Row="0" Visibility="{TemplateBinding ComputedVerticalScrollBarVisibility}" Value="{Binding VerticalOffset, Mode=OneWay, RelativeSource={RelativeSource TemplatedParent}}" ViewportSize="{TemplateBinding ViewportHeight}"/> 
     <ScrollBar x:Name="PART_HorizontalScrollBar" AutomationProperties.AutomationId="HorizontalScrollBar" Cursor="Arrow" Grid.Column="0" Maximum="{TemplateBinding ScrollableWidth}" Minimum="0" Orientation="Horizontal" Grid.Row="1" Visibility="{TemplateBinding ComputedHorizontalScrollBarVisibility}" Value="{Binding HorizontalOffset, Mode=OneWay, RelativeSource={RelativeSource TemplatedParent}}" ViewportSize="{TemplateBinding ViewportWidth}"/> 
    </Grid> 
</ControlTemplate>