protected override Size MeasureOverride(Size availableSize)
{
var itemsControl = ItemsControl.GetItemsOwner(this);
var itemCount = itemsControl.HasItems ? itemsControl.Items.Count : 0;
var firstVisibleItemIndex = Math.Max(SelectedIndex - NumberVisible, 0);
var lastVisibleItemIndex = Math.Min(SelectedIndex + NumberVisible, itemCount - 1);
var children = InternalChildren;
var generator = ItemContainerGenerator;
var startPos = generator.GeneratorPositionFromIndex(firstVisibleItemIndex);
var childIndex = (startPos.Offset == 0) ? startPos.Index : startPos.Index + 1;
var inserted = 0;
using (generator.StartAt(startPos, GeneratorDirection.Forward, true))
{
for (var itemIndex = firstVisibleItemIndex; itemIndex <= lastVisibleItemIndex; ++itemIndex, ++childIndex)
{
bool newlyRealized;
// Get or create the child
var child = generator.GenerateNext(out newlyRealized) as UIElement;
if (newlyRealized)
{
// Figure out if we need to insert the child at the end or somewhere in the middle
if (childIndex >= children.Count)
{
AddInternalChild(child);
inserted++;
}
else
{
InsertInternalChild(childIndex, child);
inserted--;
}
if (child != null)
{
generator.PrepareItemContainer(child);
}
}
}
}
CleanUpItems(firstVisibleItemIndex, lastVisibleItemIndex);
if (StoredSelectedIndex != SelectedIndex)
{
StoredSelectedIndex = SelectedIndex;
CurrentView.Anima(GetPositionIndex(SelectedIndex), NumberVisible, inserted);
}
if (availableSize.Width == double.PositiveInfinity || availableSize.Height == double.PositiveInfinity)
{
return(new Size());
}
return(availableSize);
}