通过 .exe WPF 运行时在滚动崩溃时将数据添加到数据网格

Question

我有一个数据网格，当剩余的记录少于 50 条时，会触发检索后续记录的事件。我在 Task.Run 中开始下载过程。

有一种情况，当用户用鼠标将滚动条滚动到末尾时，程序开始永远下载新记录。 当我通过 Visual Studio 运行程序时，界面没有崩溃，我可以通过向上移动滚动条来中断下载。

但是当通过.exe启动程序时，界面被冻结，无法进行任何操作。

在这种情况下，总是 e.ExtentHeight - e.VerticalOffset == 27。

我尝试在每次调用下载后以某种方式设置滚动条以获得 e.ExtentHeight - e.VerticalOffset> 50。但我不知道如何为 DataGrid 执行此操作我只看到 ScrollIntoView () 但是当我使用它时我没有看到任何变化。

我做了一个测试程序，当.exe启动时出现同样的问题：

public partial class MainWindow : Window
{

    public List<Event> EventsList { get; set; }
    public MainWindow()
    {
        InitializeComponent();
        EventsList = new List<Event>();
    }

    private void EventDataGrid_ScrollChanged(object sender, ScrollChangedEventArgs e)
    {
        Task.Run(() =>
        {
            if (e.ExtentHeight - 50 < e.VerticalOffset)
                TakeEvents();
        });
    }
    Random r = new Random();
    int lastIndex = 0;
    private void TakeEvents()
    {
        Stopwatch s = new Stopwatch();
        s.Start();

        for (int i = 0; i < 900; i++)
        {
            EventsList.Add(new Event()
            {
                Device = 1,
                Index = lastIndex++
            });
        }
        s.Stop();
        RefreshEventsList();
    }
    private void RefreshEventsList()
    {
        Task.Run(() =>
        {
            Dispatcher.Invoke(() =>
            {
                var filtrList = EventsList.Where(x => x != null && x.Device != 0).ToList();
                EventsDataGrid.ItemsSource = filtrList;
            });
        });
    }

}
public class Event
{
    public int Index { get; set; }
    public int Device { get; set; }
}

XAML：

<Grid>
    <DataGrid x:Name="EventsDataGrid" FontSize="15" Grid.Row="1" AutoGenerateColumns="False" ItemsSource="{Binding}" IsReadOnly="True" ScrollViewer.HorizontalScrollBarVisibility="Disabled" VerticalAlignment="Stretch" 
                  Background="Transparent" Foreground="Black" HeadersVisibility="Column" VerticalScrollBarVisibility="Visible" BorderThickness="0" ScrollViewer.ScrollChanged="EventDataGrid_ScrollChanged" >
        <DataGrid.Columns>
            <DataGridTextColumn Width="*" Binding="{Binding Index}" Header="Index" Foreground="Black"/>
            <DataGridTextColumn Width="*" Binding="{Binding Device}" Header="Device" Foreground="Black"/>
        </DataGrid.Columns>
    </DataGrid>
</Grid>

Answer 1

不确定您的代码到底应该做什么，但您至少应该进行以下修改：

使 ScrollChanged 处理程序异步并等待任务。如果没有必要，不要运行任务：

private async void EventDataGrid_ScrollChanged(object sender, ScrollChangedEventArgs e)
{
    if (e.ExtentHeight - 50 < e.VerticalOffset)
    {
        await Task.Run(TakeEvents);
    }
}

在后台线程中创建过滤后的List，不要为了调用Dispatcher.Invoke而运行Task：

private void TakeEvents()
{
    ...
    s.Stop();

    var filteredList = EventsList.Where(e => e.Device != 0).ToList();

    Dispatcher.Invoke(() => EventsDataGrid.ItemsSource = filteredList);
}

Answer 2

尝试以下，放置一些cmets如果不清楚请留下cmets

public partial class MainWindow : Window
{

    public List<Event> EventsList { get; set; }
    public MainWindow()
    {
        InitializeComponent();
        EventsList = new List<Event>();
    }

    private void EventDataGrid_ScrollChanged(object sender, ScrollChangedEventArgs e)
    {
        if (_blockRefresh)
            return;

        if (e.ExtentHeight - 50 < e.VerticalOffset)
            TakeEvents();
    }
    private int _lastIndex = 0;
    private bool _blockRefresh;

    private void TakeEvents()
    {
        Stopwatch s = new Stopwatch();
        s.Start();

        for (int i = 0; i < 900; i++)
        {
            EventsList.Add(new Event()
            {
                Device = 1,
                Index = _lastIndex++
            });
        }
        s.Stop();
        RefreshEventsList();
    }
    private void RefreshEventsList()
    {
        _blockRefresh = true;
        _ = Dispatcher.BeginInvoke((Action)(() =>
        {
            var oldList = EventsDataGrid.ItemsSource as IList<Event>;
            var oldIndex = oldList?.Count - 1 ?? -1;
            var filterList = EventsList.Where(x => x != null && x.Device != 0).ToList();

            EventsDataGrid.ItemsSource = filterList;
            
            //scroll to the previous last item, to prevent the condition e.ExtentHeight - 50 < e.VerticalOffset to be true once again prevents endless loop
            //scrolling will jump if scrollbar is moved by holding the left mouse button
            if (oldIndex != -1)
                EventsDataGrid.ScrollIntoView(oldIndex);

            _ = Dispatcher.BeginInvoke((Action)(() =>
            {
                //when UI updated "unlock" the refresh routine
                _blockRefresh = false;
            }), DispatcherPriority.ApplicationIdle);
        }), DispatcherPriority.ApplicationIdle);
    }
}