private void RecycleItems(ItemLayoutInfo layoutInfo)
{
foreach (UIElement child in Children.OfType <UIElement>())
{
int virtualItemIndex = GetVirtualItemIndex(child);
if (virtualItemIndex < layoutInfo.FirstRealizedItemIndex || virtualItemIndex > layoutInfo.LastRealizedItemIndex)
{
GeneratorPosition generatorPosition = itemsGenerator.GeneratorPositionFromIndex(virtualItemIndex);
if (generatorPosition.Index >= 0)
{
itemsGenerator.Recycle(generatorPosition, 1);
}
}
SetVirtualItemIndex(child, -1);
}
}
protected override Size MeasureOverride(Size availableSize)
{
if (itemsControl == null)
{
return(new Size(double.IsInfinity(availableSize.Width) ? 0 : availableSize.Width,
double.IsInfinity(availableSize.Height) ? 0 : availableSize.Height));
}
isInMeasure = true;
childLayouts.Clear();
ExtentInfo extentInfo = GetExtentInfo(availableSize);
EnsureScrollOffsetIsWithinConstrains(extentInfo);
ItemLayoutInfo layoutInfo = GetLayoutInfo(availableSize, ItemHeight, extentInfo);
RecycleItems(layoutInfo);
// Determine where the first item is in relation to previously realized items
GeneratorPosition generatorStartPosition = itemsGenerator.GeneratorPositionFromIndex(layoutInfo.FirstRealizedItemIndex);
var visualIndex = 0;
double currentX = layoutInfo.FirstRealizedItemLeft;
double currentY = layoutInfo.FirstRealizedLineTop;
using (itemsGenerator.StartAt(generatorStartPosition, GeneratorDirection.Forward, true))
{
for (int itemIndex = layoutInfo.FirstRealizedItemIndex; itemIndex <= layoutInfo.LastRealizedItemIndex; itemIndex++, visualIndex++)
{
bool newlyRealized;
var child = (UIElement)itemsGenerator.GenerateNext(out newlyRealized);
SetVirtualItemIndex(child, itemIndex);
if (newlyRealized)
{
InsertInternalChild(visualIndex, child);
}
else
{
// check if item needs to be moved into a new position in the Children collection
if (visualIndex < Children.Count)
{
if (!Equals(Children[visualIndex], child))
{
int childCurrentIndex = Children.IndexOf(child);
if (childCurrentIndex >= 0)
{
RemoveInternalChildRange(childCurrentIndex, 1);
}
InsertInternalChild(visualIndex, child);
}
}
else
{
// we know that the child can't already be in the children collection
// because we've been inserting children in correct visualIndex order,
// and this child has a visualIndex greater than the Children.Count
AddInternalChild(child);
}
}
// only prepare the item once it has been added to the visual tree
itemsGenerator.PrepareItemContainer(child);
child.Measure(new Size(ItemWidth, ItemHeight));
childLayouts.Add(child, new Rect(currentX, currentY, ItemWidth, ItemHeight));
if (currentX + ItemWidth * 2 >= availableSize.Width)
{
// wrap to a new line
currentY += ItemHeight;
currentX = 0;
}
else
{
currentX += ItemWidth;
}
}
}
RemoveRedundantChildren();
UpdateScrollInfo(availableSize, extentInfo);
var desiredSize = new Size(double.IsInfinity(availableSize.Width) ? 0 : availableSize.Width,
double.IsInfinity(availableSize.Height) ? 0 : availableSize.Height);
isInMeasure = false;
return(desiredSize);
}
