ItemsControl 未虚拟化

Question

我无法让这个 ItemsControl 正确虚拟化。调试显示集合已快速初始化，但所有项目都被添加到控件而不是子集（我只是将 TracePoint 放在构成项目的 TextBox_Initializeevent in theUserControl` 中）。

注意：我看过其他类似的问题，但无法用这些答案解决这个问题。

视图模型：

public class ImportInformationViewModel : CommandViewModel
{
    public ImportInformationViewModel()
    {

        this.PropertyChanged += ImportInformationViewModel_PropertyChanged;
    }

    private ObservableCollection<SingleTransactionViewModel> mTransactions;
    public ReadOnlyObservableCollection<SingleTransactionViewModel> Transactions
    {
        get
        {
            if (mTransactions == null)
                mTransactions = new ObservableCollection<SingleTransactionViewModel>();

            var filtered = mTransactions.Where(trans => !trans.IgnoreTransaction)
                .OrderBy(trans => trans.DateStamp)
                .ThenBy(trans => trans.TransactionName)
                .ThenBy(trans => trans.TransactionDetail);

            return new ReadOnlyObservableCollection<SingleTransactionViewModel>(new ObservableCollection<SingleTransactionViewModel>(filtered));
        }
    }

    private void ImportInformationViewModel_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
    {
        if (e.PropertyName == "TransactionFileName")
        {
            if (File.Exists(mTransactionFileName))
           {
                mTransactions.Clear();
                // Process File (Not Shown)
                mTransactions.Add(new SingleTransactionViewModel()
                {
                    DateStamp = date,
                    TransactionDetail = someText;
                });
            }
        }

        if (e.PropertyName != "Transactions")
            NotifyPropertyChanged("Transactions");
    }
}

SingleTransactionViewModel 只是实现 INotifyPropertyChanged 的另一个 class。没什么特别的。

这是包含 ItemsControl

的控件

<UserControl x:Class="ImportInformationView">
    <UserControl.Resources>
        <CollectionViewSource x:Key="TransactionsData" Source="{Binding Transactions}">
            <CollectionViewSource.GroupDescriptions>
                <PropertyGroupDescription PropertyName="YearAndMonth" />
            </CollectionViewSource.GroupDescriptions>
        </CollectionViewSource>

        <BooleanToVisibilityConverter x:Key="booleanToVisibility" />
    </UserControl.Resources>
    <ItemsControl ItemsSource="{Binding Source={StaticResource TransactionsData}}"
                        HorizontalAlignment="Stretch"
                        HorizontalContentAlignment="Stretch"
                        ScrollViewer.CanContentScroll="True"
                        VirtualizingStackPanel.IsVirtualizing="True"
                        VirtualizingStackPanel.VirtualizationMode="Recycling"
                        MinHeight="20">
            <ItemsControl.GroupStyle>
                <GroupStyle>
                    <GroupStyle.ContainerStyle>
                        <Style TargetType="{x:Type GroupItem}">
                            <Setter Property="Template">
                                <Setter.Value>
                                    <ControlTemplate TargetType="{x:Type GroupItem}">
                                        <GroupBox Padding="5" Margin="2,5">
                                            <GroupBox.Header>
                                                <Border Background="Black"
                                                        CornerRadius="4">
                                                    <TextBlock Text="{Binding Name}" />
                                                </Border>
                                            </GroupBox.Header>
                                            <ItemsPresenter />
                                        </GroupBox>
                                    </ControlTemplate>
                                </Setter.Value>
                            </Setter>
                        </Style>
                    </GroupStyle.ContainerStyle>
                </GroupStyle>
            </ItemsControl.GroupStyle>
            <ItemsControl.Template>
                <ControlTemplate>
                    <ScrollViewer CanContentScroll="True">
                        <ItemsPresenter SnapsToDevicePixels="{TemplateBinding UIElement.SnapsToDevicePixels}" />
                    </ScrollViewer>
                </ControlTemplate>
            </ItemsControl.Template>
            <ItemsControl.ItemsPanel>
                <ItemsPanelTemplate>
                    <UniformGrid IsItemsHost="True" Columns="2" Grid.IsSharedSizeScope="True" VirtualizingStackPanel.IsVirtualizing="True" />
                    <!--<VirtualizingStackPanel IsItemsHost="True" />-->
                </ItemsPanelTemplate>
            </ItemsControl.ItemsPanel>
            <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <views:SingleTransactionView Margin="4,6" />
                </DataTemplate>
            </ItemsControl.ItemTemplate>
        </ItemsControl>
    </UserControl>

我已经将 SingleTransactionView 简化为非常简单的东西：

    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="Auto" SharedSizeGroup="ExpanderColumn" />
        <ColumnDefinition Width="*" SharedSizeGroup="TransactionNameColumn" />
        <ColumnDefinition Width="Auto" SharedSizeGroup="DateColumn" />
        <ColumnDefinition Width="Auto" SharedSizeGroup="OptionsColumn" />
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto" />
        <RowDefinition Height="Auto" />
    </Grid.RowDefinitions>


    <TextBlock Grid.Column="1"
               Grid.Row="0"
               Initialized="TextBlock_Initialized"
               Text="{Binding TransactionName}"
               HorizontalAlignment="Left"
               VerticalAlignment="Center"
               FontSize="14"
               FontWeight="Bold"
               Margin="4"/>        
</Grid>

Answer 1

这可能是由于您使用了分组。默认情况下，启用分组会有效地关闭虚拟化。但是，从 .NET 4.5 开始，您应该能够通过 VirtualizingPanel.IsVirtualizingWhenGrouping 属性.

重新获得此功能

摘自 this blog post 关于 .NET 4.5 中的 WPF 增强功能：

In WPF 4.0, you lost virtualization when grouping is done on the collection you display. I repeat : Grouping = no virtualization in WPF 4.0. This is still the default behavior of WPF 4.5, but you can turn on the virtualization by using the IsVirtualizingWhenGrouping attached property of the VirtualizingPanel class. When this is done, you benefit of all the already described advantages of virtualization.

Here is how you can enable it via XAML:
<ListBox ItemsSource="{Binding Persons}"
         ItemTemplate="{StaticResource PersonDataTemplate}"
         VirtualizingPanel.IsVirtualizing="True"
         VirtualizingPanel.IsVirtualizingWhenGrouping="True">
    <ListBox.GroupStyle>
        <GroupStyle HeaderTemplate="{StaticResource GroupHeaderTemplate}" />
    </ListBox.GroupStyle>
</ListBox>

听起来像设置 VirtualizingPanel.IsVirtualizingWhenGrouping="True" 以及其他与虚拟化相关的属性应该会给你想要的行为。+

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