WPF列表框自动滚动的同时拖动 [英] WPF Listbox auto scroll while dragging

问题描述

我有，有一个的ListBox 一个WPF应用程序。拖动机制已经实施，但是当列表太长，我想一个项目移动到的位置不可见我不能。

I have a WPF app that has a ListBox. The drag mechanism is already implemented, but when the list is too long and I want to move an item to a position not visible I can't.

例如，屏幕上显示10个项目。我有20个项目。如果我要到最后一个项目拖动到第一个位置，我必须拖动到顶部和下降。向上滚动并再次拖动。

For example, the screen shows 10 items. And I have 20 items. If I want to drag the last item to the first position I must drag to the top and drop. Scroll up and drag again.

我怎样才能让的ListBox 自动滚动？

How can I make the ListBox auto scroll?

推荐答案

明白了。使用的事件的dragover 的的ListBox ，用于发现功能的这里得到列表框，后的ScrollViewer ，它只是有点杂耍与位置。

Got it. Used the event DragOver of the ListBox, used the function found here to get the scrollviewer of the listbox and after that its just a bit of juggling with the Position.

private void ItemsList_DragOver(object sender, System.Windows.DragEventArgs e)
{
    ListBox li = sender as ListBox;
    ScrollViewer sv = FindVisualChild<ScrollViewer>(ItemsList);

    double tolerance = 10;
    double verticalPos = e.GetPosition(li).Y;
    double offset = 3;

    if (verticalPos < tolerance) // Top of visible list?
    {
        sv.ScrollToVerticalOffset(sv.VerticalOffset - offset); //Scroll up.
    }
    else if (verticalPos > li.ActualHeight - tolerance) //Bottom of visible list?
    {
        sv.ScrollToVerticalOffset(sv.VerticalOffset + offset); //Scroll down.    
    }
}

public static childItem FindVisualChild<childItem>(DependencyObject obj) where childItem : DependencyObject
{
    // Search immediate children first (breadth-first)
    for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
    {
        DependencyObject child = VisualTreeHelper.GetChild(obj, i);

        if (child != null && child is childItem)
            return (childItem)child;

        else
        {
            childItem childOfChild = FindVisualChild<childItem>(child);

            if (childOfChild != null)
                return childOfChild;
        }
    }

    return null;
}

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