private void SetItemsHostInsetForChild(int index, UIElement child, IContainItemStorage itemStorageProvider, bool isHorizontal)
{
Debug.Assert(!IsVSP45Compat, "SetItemsHostInset should not be called in VSP45-compat mode");
// this only applies to a hierarchical element with a visible ItemsHost
bool isChildHorizontal = isHorizontal;
IHierarchicalVirtualizationAndScrollInfo virtualizingChild = GetVirtualizingChild(child, ref isChildHorizontal);
Panel itemsHost = (virtualizingChild == null) ? null : virtualizingChild.ItemsHost;
if (itemsHost == null || !itemsHost.IsVisible)
return;
// get the transformation from child coords to itemsHost coords
GeneralTransform transform = child.TransformToDescendant(itemsHost);
if (transform == null)
return; // when transform is undefined, ItemsHost is effectively invisible
// build a rect (in child coords) describing the child's extended frame
FrameworkElement fe = virtualizingChild as FrameworkElement;
Thickness margin = (fe == null) ? new Thickness() : fe.Margin;
Rect childRect = new Rect(new Point(), child.DesiredSize);
childRect.Offset(-margin.Left, -margin.Top);
// transform to itemsHost coords
Rect itemsRect = transform.TransformBounds(childRect);
// compute the desired inset, avoiding catastrophic cancellation errors
Size itemsSize = itemsHost.DesiredSize;
double left = DoubleUtil.AreClose(0, itemsRect.Left) ? 0 : -itemsRect.Left;
double top = DoubleUtil.AreClose(0, itemsRect.Top) ? 0 : -itemsRect.Top;
double right = DoubleUtil.AreClose(itemsSize.Width, itemsRect.Right) ? 0 : itemsRect.Right-itemsSize.Width;
double bottom = DoubleUtil.AreClose(itemsSize.Height, itemsRect.Bottom) ? 0 : itemsRect.Bottom-itemsSize.Height;
Thickness inset = new Thickness(left, top, right, bottom);
// get the item to use as the key into items storage
object item = GetItemFromContainer(child);
if (item == DependencyProperty.UnsetValue)
{
Debug.Assert(false, "SetInset should only be called for a container");
return;
}
// see whether inset is changing
object box = itemStorageProvider.ReadItemValue(item, ItemsHostInsetProperty);
bool changed = (box == null);
bool remeasure = changed;
if (!changed)
{
Thickness oldInset = (Thickness)box;
changed = !( DoubleUtil.AreClose(oldInset.Left, inset.Left) &&
DoubleUtil.AreClose(oldInset.Top, inset.Top ) &&
DoubleUtil.AreClose(oldInset.Right, inset.Right) &&
DoubleUtil.AreClose(oldInset.Bottom, inset.Bottom) );
// only changes along the scrolling axis require a remeasure.
// use a less stringent "AreClose" test; experiments show that the
// trailing inset can change due to roundoff error by an amount
// that is larger than the tolerance in DoubleUtil, but not large
// enough to warrant an expensive remeasure.
remeasure = changed &&
( (isHorizontal && !(AreInsetsClose(oldInset.Left, inset.Left) &&
AreInsetsClose(oldInset.Right, inset.Right)))
|| (!isHorizontal && !(AreInsetsClose(oldInset.Top, inset.Top) &&
AreInsetsClose(oldInset.Bottom, inset.Bottom))) );
}
if (changed)
{
// store the new inset
itemStorageProvider.StoreItemValue(item, ItemsHostInsetProperty, inset);
child.SetValue(ItemsHostInsetProperty, inset);
}
if (remeasure)
{
// re-measure the scrolling panel
ItemsControl scrollingItemsControl = GetScrollingItemsControl(child);
Panel scrollingPanel = (scrollingItemsControl == null) ? null : scrollingItemsControl.ItemsHost;
if (scrollingPanel != null)
{
VirtualizingStackPanel vsp = scrollingPanel as VirtualizingStackPanel;
if (vsp != null)
{
vsp.AnchoredInvalidateMeasure();
}
else
{
scrollingPanel.InvalidateMeasure();
}
}
}
}