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.
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.
How can I make the ListBox
auto scroll?
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;
}