private bool HandleScrollByPage(bool up)
{
// NOTE: This implementation assumes that items are laid out
// vertically and the Headers of the TreeViewItems appear above
// their ItemsPresenter. The same assumptions are made in WPF.
ScrollViewer scrollHost = ItemsControlHelper.ScrollHost;
if (scrollHost != null)
{
double viewportHeight = scrollHost.ViewportHeight;
double top;
double bottom;
(SelectedContainer.HeaderElement ?? SelectedContainer).GetTopAndBottom(scrollHost, out top, out bottom);
TreeViewItem selected = null;
TreeViewItem next = SelectedContainer;
ItemsControl parent = SelectedContainer.ParentItemsControl;
if (parent != null)
{
// We need to start at the root TreeViewItem if we're
// scrolling up, but can start at the SelectedItem if
// scrolling down.
if (up)
{
while (parent != this)
{
TreeViewItem parentItem = parent as TreeViewItem;
if (parentItem == null)
{
break;
}
ItemsControl grandparent = parentItem.ParentItemsControl;
if (grandparent == null)
{
break;
}
next = parentItem;
parent = grandparent;
}
}
int index = parent.ItemContainerGenerator.IndexFromContainer(next);
int count = parent.Items.Count;
while (parent != null && next != null)
{
if (next.IsEnabled)
{
double delta;
if (next.HandleScrollByPage(up, scrollHost, viewportHeight, top, bottom, out delta))
{
// This item or one of its children was focused
return(true);
}
else if (NumericExtensions.IsGreaterThan(delta, viewportHeight))
{
// If the item doesn't fit on the page but it's
// already selected, we'll select the next item
// even though it doesn't completely fit into
// the current view
if (selected == SelectedContainer || selected == null)
{
return(up ?
SelectedContainer.HandleUpKey() :
SelectedContainer.HandleDownKey());
}
break;
}
else
{
selected = next;
}
}
index += up ? -1 : 1;
if (0 <= index && index < count)
{
next = parent.ItemContainerGenerator.ContainerFromIndex(index) as TreeViewItem;
}
else if (parent == this)
{
// We just finished with the last item in the
// TreeView
next = null;
}
else
{
// Move up the parent chain to the next item
while (parent != null)
{
TreeViewItem oldParent = parent as TreeViewItem;
parent = oldParent.ParentItemsControl;
if (parent != null)
{
count = parent.Items.Count;
index = parent.ItemContainerGenerator.IndexFromContainer(oldParent) + (up ? -1 : 1);
if (0 <= index && index < count)
{
next = parent.ItemContainerGenerator.ContainerFromIndex(index) as TreeViewItem;
break;
}
else if (parent == this)
{
next = null;
parent = null;
}
}
}
}
}
}
if (selected != null)
{
if (up)
{
if (selected != SelectedContainer)
{
return(selected.Focus());
}
}
else
{
selected.FocusInto();
}
}
}
return(false);
}
