c# - ListBox DragDrop 自动滚动问题？

Question

我已经使用以下方法在列表框中成功实现了拖放:

Bea Stollnitz - 如何在数据绑定(bind)的 ItemsControl 之间拖放项目: http://www.zagstudio.com/blog/488#.U15ozvldU9Y

但是，当列表有一个滚动条并且我在列表的末尾时，当我拖动一个项目时，ListBox 不会自动滚动。
我如何融入这种行为？

编辑:当我越过列表的底部边框时，我希望它滚动以便我可以放在较低的项目上的某个地方？

Answer 1

我使用附加属性实现此目的，该属性添加了在拖动时鼠标向其顶部或底部移动时滚动控件的功能。这是附加的属性类:-

public class DragDropAttProps
{
    public static readonly DependencyProperty ScrollOnDragDropProperty =
        DependencyProperty.RegisterAttached(
            "ScrollOnDragDrop",
            typeof(bool),
            typeof(DragDropAttProps),
            new PropertyMetadata(false, HandleScrollOnDragDropChanged));

    public static bool GetScrollOnDragDrop(DependencyObject element)
    {
        return (bool)element.GetValue(ScrollOnDragDropProperty);
    }
    public static void SetScrollOnDragDrop(DependencyObject element, bool value)
    {
        element.SetValue(ScrollOnDragDropProperty, value);
    }

    private static void HandleScrollOnDragDropChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var container = d as FrameworkElement;
        if (d == null)
        {
            Debug.Fail("Invalid type!");
        }

        Unsubscribe(container);

        if (true.Equals(e.NewValue))
        {
            Subscribe(container);
        }
    }

    private static void Subscribe(FrameworkElement container)
    {
        container.PreviewDragOver += OnContainerPreviewDragOver;
    }

    private static void Unsubscribe(FrameworkElement container)
    {
        container.PreviewDragOver -= OnContainerPreviewDragOver;
    }

    private static void OnContainerPreviewDragOver(object sender, DragEventArgs e)
    {
        const double Tolerance = 60;
        const double Offset = 20;

        var container = sender as FrameworkElement;
        if (container == null)
        {
            return;
        }

        var scrollViewer = GetFirstVisualChild<ScrollViewer>(container); 
        if (scrollViewer == null)
        {
            return;
        }

        var verticalPos = e.GetPosition(container).Y;

        if (verticalPos < Tolerance)
        {
            // Top of visible list? Scroll up.
            scrollViewer.ScrollToVerticalOffset(scrollViewer.VerticalOffset - Offset);
        }
        else if (verticalPos > container.ActualHeight - Tolerance) 
        {
            // Bottom of visible list? Scroll down.
            scrollViewer.ScrollToVerticalOffset(scrollViewer.VerticalOffset + Offset);
        }
    }

    private static T GetFirstVisualChild<T>(DependencyObject depObj) where T : DependencyObject
    {
        if (depObj != null)
        {
            for (var i = 0; i < VisualTreeHelper.GetChildrenCount(depObj); i++)
            {
                var child = VisualTreeHelper.GetChild(depObj, i);
                if (child is T)
                {
                    return (T)child;
                }

                var childItem = GetFirstVisualChild<T>(child);
                if (childItem != null)
                {
                    return childItem;
                }
            }
        }

        return null;
    }
}

最后，在控件的 XAML 上指定附加属性。免责声明:我在 TreeView 上使用这种方法，但它应该适用于任何可滚动控件，例如列表框:-

<UserControl xmlns:attProps="clr-namespace:MyAssembly.AttachedProperties;assembly=MyAssembly">

    <TreeView attProps:DragDropAttProps.ScrollOnDragDrop="True">