GridView 丢失了对非索引位置中的项目的跟踪，并且许多项目不再显示

我正在使用 UWP 应用程序FileInformationFactory检索文件对象的虚拟化向量，该向量被转换为FileInformation并显示在GridView.

我想查询插入笔记本电脑的 SD 卡上的文件夹并比较该文件夹的虚拟化情况GridView当此文件夹位于FullyIndexed位置，例如我的桌面。

该 SD 卡有一个包含 15,000 个零字节文本文件的文件夹。每个文件都有命名x.txt其中 x 的范围是 1-15000（这可以通过单击下面代码中的“添加”按钮在您选择的文件夹中生成；在我的机器上需要一分钟左右的时间，但请记住只执行一次！）。

结果显示在GridView我在其中显示每个文件的名称。

In a FullyIndexed我可以上下滚动的位置GridView非常快，即使使用垂直滚动条也非常快且不稳定，并且GridView尽管会有几秒钟的延迟，但总是会设法显示每个文件的名称。

In a NotIndexed在 SD 卡或外部硬盘等位置，当我缓慢滚动时 GridView 会显示项目，但当我上下滚动太快时，GridView 会很快失去对项目的跟踪，例如当我的触控板使用垂直滚动条时。等待没有帮助。该应用程序仍然响应，但没有任何显示。即使向上滚动到顶部，也仅显示第一个元素名称，唯一的选择是重新显示整体并平滑滚动。

我怎样才能解决这个问题NotIndexed地点？我不想将文件一一检索到内存中，因为这会占用太多时间，而且对于真实照片来说，会很快耗尽用户的 RAM。因此使用GetVirtualizedFilesVector.

我以为这将是 GridView 的虚拟化，但事实似乎并非如此，而且该应用程序可以很好地处理真实的 17k 照片，但只能在FullyIndexed地点。 谢谢

<Page
x:Class="Virtualization.Scenario4"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:ba="using:Windows.Storage.BulkAccess"
xmlns:local="using:Virtualization"
mc:Ignorable="d"
Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="auto"/>
        <RowDefinition Height="*"/>
        <RowDefinition Height="auto"/>
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="auto"/>
        <ColumnDefinition Width="*"/>
        <ColumnDefinition Width="auto"/>
        <ColumnDefinition Width="48"/>
    </Grid.ColumnDefinitions>
    <StackPanel Grid.ColumnSpan="1" Orientation="Horizontal"
                BorderThickness="0,0,2,2">
        <AppBarButton x:Name="FolderPickerButton" Icon="Folder"
                      LabelPosition="Collapsed" Label="Select Folder"
                      Click="FolderPickerButton_Click"/>
        <AppBarButton Icon="ViewAll"
                      LabelPosition="Collapsed"
                      Click="ViewAllAppBarButton_Click"/>
        <AppBarButton Icon="Add"
                      LabelPosition="Collapsed"
                      Click="AddFilesAppBarButton_Click"/>
        <AppBarSeparator/>
    </StackPanel>
    <GridView Grid.Row="1" Grid.Column="1"
              ItemsSource="{x:Bind ItemCollectionView, Mode=OneWay}" IsItemClickEnabled="True" ItemClick="GridView_ItemClick">
        <GridView.ItemTemplate>
            <DataTemplate x:DataType="ba:FileInformation">
                <Grid>
                    <TextBlock MinWidth="80" Text="{Binding Name}" TextWrapping="WrapWholeWords"/>
                </Grid>
            </DataTemplate>
        </GridView.ItemTemplate>
    </GridView>

    <ListView Grid.Row="1" Grid.Column="2" ItemsSource="{x:Bind Information, Mode=OneWay}">
        <ListView.ItemTemplate>
            <DataTemplate>
                <TextBlock Text="{Binding}"/>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>

</Grid>

public sealed partial class Scenario4 : Page, INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    public void OnPropertyChanged([CallerMemberName] string propertyName = null)
      => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    public Scenario4()
    {
        this.InitializeComponent();
    }

    private ICollectionView _fileCollectionView;
    private StorageFolder _folder;
    private IStorageQueryResultBase _query;
    private FileInformationFactory _fileInformationFactory;
    private object _vector;

    public CollectionViewSource CollectionViewSource { get; set; } = new CollectionViewSource();
    public ICollectionView ItemCollectionView
    {
        get { return _fileCollectionView; }
        set
        {
            if (_fileCollectionView != value)
            {
                _fileCollectionView = value;
                OnPropertyChanged(nameof(ItemCollectionView));
            }
        }
    }
    public ObservableCollection<string> Information { get; private set; } = new ObservableCollection<string>();

    private async void FolderPickerButton_Click(object sender, RoutedEventArgs e)
    {
        var _pickedFolder = await PickFolderAsync();
        if (_pickedFolder == null)
        {
            Information.Add("Choose a folder");
            return;
        }
        Information.Add("Generate 15k files with the Add button if not done already, otherwise click the ViewAll button");
        _folder = _pickedFolder;
    }

    private async void Query_ContentsChanged(IStorageQueryResultBase sender, object args)
    {
        await CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, async () =>
        {
            Information.Add($"Contents Changed {sender.Folder.Name} {args}");
        });
    }

    private void View_VectorChanged(IObservableVector<object> sender, IVectorChangedEventArgs @event)
    {
        if (@event.CollectionChange == CollectionChange.Reset)
        {
            Information.Add($"Vector Changed {@event.CollectionChange} ItemCount: {sender.Count} Index: {@event.Index}");
        }
    }


    private static async Task<StorageFolder> PickFolderAsync()
    {
        var folderPicker = new FolderPicker
        {
            SuggestedStartLocation = PickerLocationId.Desktop,
            ViewMode = PickerViewMode.Thumbnail
        };

        folderPicker.FileTypeFilter.Add("*");

        var _pickedFolder = await folderPicker.PickSingleFolderAsync();
        return _pickedFolder;
    }

    private void GridView_ItemClick(object sender, ItemClickEventArgs e)
    {
        if (e.ClickedItem is FileInformation fileInformation)
        {
            Information.Add(fileInformation.Name);
        }
        else
        {
            if (e.ClickedItem == null)
            {
                Information.Add("Null");
            }
            else
            {
                Information.Add(e.ClickedItem.ToString());
            }
        }
    }

    private async void AddFilesAppBarButton_Click(object sender, RoutedEventArgs e)
    {

        for (int i = 1; i <= 15000; i++)
        {
            await _folder.CreateFileAsync(i + ".txt", CreationCollisionOption.ReplaceExisting);
            if (i % 250 == 0)
            {
                Information.Add(i.ToString());
            }
        }
    }

    private async void ViewAllAppBarButton_Click(object sender, RoutedEventArgs e)
    {
        if (_folder == null)
        {
            Information.Add("Choose folder first");
            return;
        }
        var state = await _folder.GetIndexedStateAsync();

        var queryOptions = new QueryOptions { FolderDepth = FolderDepth.Deep, IndexerOption = IndexerOption.UseIndexerWhenAvailable };


        Information.Add($"{_folder.Name} is {state} {queryOptions.IndexerOption}");

        _query = _folder.CreateFileQueryWithOptions(queryOptions);

        var st = Stopwatch.StartNew();
        var numOfFiles = (await _query.GetItemCountAsync());
        st.Stop();

        Information.Add($"{state} {queryOptions.IndexerOption}. Found {numOfFiles} in {st.ElapsedMilliseconds / 1000.0}");
        if (numOfFiles==0)
        {
            Information.Add("Generate files by clicking the Add button");
            return;
        }
        _fileInformationFactory = new FileInformationFactory(_query, ThumbnailMode.SingleItem, Constants.Thumbnail_Size,
           ThumbnailOptions.UseCurrentScale, delayLoad: false);

        _vector = _fileInformationFactory.GetVirtualizedFilesVector();
        CollectionViewSource.Source = _vector;

        ItemCollectionView = CollectionViewSource.View;
        _query.ContentsChanged += Query_ContentsChanged;
        CollectionViewSource.View.VectorChanged += View_VectorChanged;
    }
}

For Constants.Thumbnail_Size，将其设置为例如100.

Addendum

该问题与外部硬盘驱动器无关。我在现代 Thinkpad X1 Yoga 3rd Gen 上创建了一个未索引的分区。该问题已重现。