我有一个ListBox
的WPF应用。拖动机制已经实现,但是当列表太长并且我想将项目移动到不可见的位置时我不能。
例如,屏幕显示10个项目。我有20件物品。如果我想将最后一项拖到第一个位置,我必须拖到顶部并放下。向上滚动并再次拖动。
如何进行ListBox
自动滚动?
答案 0 :(得分:30)
知道了。使用DragOver
的事件ListBox
,使用找到的函数here来获取列表框的scrollviewer
,之后只需稍微处理位置。< / p>
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;
}
答案 1 :(得分:16)
基于此,我创建了一个Attached Behavior,可以像这样轻松使用 -
<ListView
xmlns:WpfExtensions="clr-namespace:WpfExtensions"
WpfExtensions:DragDropExtension.ScrollOnDragDrop="True"
以下是附加行为的代码 -
/// <summary>
/// Provides extended support for drag drop operation
/// </summary>
public static class DragDropExtension
{
public static read-only DependencyProperty ScrollOnDragDropProperty =
DependencyProperty.RegisterAttached("ScrollOnDragDrop",
typeof(bool),
typeof(DragDropExtension),
new PropertyMetadata(false, HandleScrollOnDragDropChanged));
public static bool GetScrollOnDragDrop(DependencyObject element)
{
if (element == null)
{
throw new ArgumentNullException("element");
}
return (bool)element.GetValue(ScrollOnDragDropProperty);
}
public static void SetScrollOnDragDrop(DependencyObject element, bool value)
{
if (element == null)
{
throw new ArgumentNullException("element");
}
element.SetValue(ScrollOnDragDropProperty, value);
}
private static void HandleScrollOnDragDropChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
FrameworkElement container = d as FrameworkElement;
if (d == null)
{
Debug.Fail("Invalid type!");
return;
}
Unsubscribe(container);
if (true.Equals(e.NewValue))
{
Subscribe(container);
}
}
private static void Subscribe(FrameworkElement container)
{
container.PreviewDragOver += OnContainerPreviewDragOver;
}
private static void OnContainerPreviewDragOver(object sender, DragEventArgs e)
{
FrameworkElement container = sender as FrameworkElement;
if (container == null)
{
return;
}
ScrollViewer scrollViewer = GetFirstVisualChild<ScrollViewer>(container);
if (scrollViewer == null)
{
return;
}
double tolerance = 60;
double verticalPos = e.GetPosition(container).Y;
double offset = 20;
if (verticalPos < tolerance) // Top of visible list?
{
scrollViewer.ScrollToVerticalOffset(scrollViewer.VerticalOffset - offset); //Scroll up.
}
else if (verticalPos > container.ActualHeight - tolerance) //Bottom of visible list?
{
scrollViewer.ScrollToVerticalOffset(scrollViewer.VerticalOffset + offset); //Scroll down.
}
}
private static void Unsubscribe(FrameworkElement container)
{
container.PreviewDragOver -= OnContainerPreviewDragOver;
}
public static T GetFirstVisualChild<T>(DependencyObject depObj) where T : DependencyObject
{
if (depObj != null)
{
for (int i = 0; i < VisualTreeHelper.GetChildrenCount(depObj); i++)
{
DependencyObject child = VisualTreeHelper.GetChild(depObj, i);
if (child != null && child is T)
{
return (T)child;
}
T childItem = GetFirstVisualChild<T>(child);
if (childItem != null)
{
return childItem;
}
}
}
return null;
}
}