wpf组合框如何处理PreviewMouseWheel

Question

我想将 MouseWheel 的处理程序添加到 ComboBox，但我不知道如何操作。

原因是我在 ScrollViewer 内的 DataGrid 内的 ComboBox 上遇到滚动问题，请参阅here，我想尝试一下。我已经有了处理 ScrollViewer 和 DataGrid 的 MouseWheel 的代码，但还没有处理 ComboBox 的代码。

<ComboBox PreviewMouseWheel="theComboBox_PreviewMouseWheel"

背后代码：

    private void theScrollViewer_PreviewMouseWheel(object sender, MouseWheelEventArgs e)
    {
        if (sender is ScrollViewer scrollView)
        {
            scrollView.UpdateLayout();
            scrollView.ScrollToVerticalOffset(scrollView.VerticalOffset - e.Delta);
            e.Handled = true;
        }            
    }

    private void theDataGrid_PreviewMouseWheel(object sender, MouseWheelEventArgs e)
    {
        var args = new MouseWheelEventArgs(e.MouseDevice, e.Timestamp, e.Delta);
        args.RoutedEvent = ScrollViewer.MouseWheelEvent;
        theScrollViewer.RaiseEvent(args);
    }

    /// <summary>
    /// The hypothetical scroll event handler, on the ComboBox,
    /// to make the ComboBox scrollable
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    private void theComboBox_PreviewMouseWheel(object sender, MouseWheelEventArgs e)
    {
        if (sender is ComboBox cb)
        {
            var args = new MouseWheelEventArgs(e.MouseDevice, e.Timestamp, e.Delta);
            args.RoutedEvent = ScrollViewer.MouseWheelEvent;
            //cb.ItemsPanel.RaiseEvents(args);//cb has no such property
            //cb.ScrollToVerticalOffset(cb.VerticalOffset - e.Delta);//cb has no such property
            //e.Handled = true;
        }
    }

Answer 1

您可以使用

ComboBox

类获取对

ScrollViewer

内部

VisualTreeHelper

的引用，然后访问其属性和方法来设置偏移量：

private void theComboBox_PreviewMouseWheel(object sender, MouseWheelEventArgs e)
{
    if (sender is ComboBox cb && e.OriginalSource is DependencyObject depObj)
    {
        ScrollViewer scrollViewer = FindParent<ScrollViewer>(depObj);
        ...
    }
}

private static T FindParent<T>(DependencyObject dependencyObject) where T : DependencyObject
{
    var parent = VisualTreeHelper.GetParent(dependencyObject);
    if (parent == null)
        return null;

    var parentT = parent as T;
    return parentT ?? FindParent<T>(parent);
}