internal void ClearElementOnDataSourceChange(VirtualizingLayoutContext context, NotifyCollectionChangedEventArgs args)
{
if (m_cachedFirstElement != null)
{
bool shouldClear = false;
switch (args.Action)
{
case NotifyCollectionChangedAction.Add:
shouldClear = args.NewStartingIndex == 0;
break;
case NotifyCollectionChangedAction.Replace:
shouldClear = args.NewStartingIndex == 0 || args.OldStartingIndex == 0;
break;
case NotifyCollectionChangedAction.Remove:
shouldClear = args.OldStartingIndex == 0;
break;
case NotifyCollectionChangedAction.Reset:
shouldClear = true;
break;
case NotifyCollectionChangedAction.Move:
throw new NotImplementedException();
}
if (shouldClear)
{
context.RecycleElement(m_cachedFirstElement);
m_cachedFirstElement = null;
}
}
}
internal void UninitializeForContext(VirtualizingLayoutContext context)
{
FlowAlgorithm.UninitializeForContext(context);
if (m_cachedFirstElement != null)
{
context.RecycleElement(m_cachedFirstElement);
}
}
// If it's realized then we shouldn't be caching it
internal void EnsureFirstElementOwnership(VirtualizingLayoutContext context)
{
if (m_cachedFirstElement != null && FlowAlgorithm.GetElementIfRealized(0) != null)
{
// We created the element, but then flowlayout algorithm took ownership, so we can clear it and
// let flowlayout algorithm do its thing.
context.RecycleElement(m_cachedFirstElement);
m_cachedFirstElement = null;
}
}
internal void ClearElementOnDataSourceChange(VirtualizingLayoutContext context, NotifyCollectionChangedEventArgs args)
{
if (m_cachedFirstElement != null)
{
// The first element of UniformGridLayout is special since we use its size to
// determine the size of all the other elements. So if the first item has changed
// we will need to clear it and re-evalauate all the items with the new item size.
bool shouldClear = false;
switch (args.Action)
{
case NotifyCollectionChangedAction.Add:
shouldClear = args.NewStartingIndex == 0;
break;
case NotifyCollectionChangedAction.Replace:
shouldClear = args.NewStartingIndex == 0 || args.OldStartingIndex == 0;
break;
case NotifyCollectionChangedAction.Remove:
shouldClear = args.OldStartingIndex == 0;
break;
case NotifyCollectionChangedAction.Reset:
shouldClear = true;
break;
case NotifyCollectionChangedAction.Move:
shouldClear = args.NewStartingIndex == 0 || args.OldStartingIndex == 0;
break;
}
if (shouldClear)
{
context.RecycleElement(m_cachedFirstElement);
m_cachedFirstElement = null;
}
}
}
internal void EnsureElementSize(
Size availableSize,
VirtualizingLayoutContext context,
double layoutItemWidth,
double LayoutItemHeight,
UniformGridLayoutItemsStretch stretch,
Orientation orientation,
double minRowSpacing,
double minColumnSpacing,
uint maxItemsPerLine)
{
if (maxItemsPerLine == 0)
{
maxItemsPerLine = 1;
}
if (context.ItemCount > 0)
{
// If the first element is realized we don't need to get it from the context
var realizedElement = FlowAlgorithm.GetElementIfRealized(0);
if (realizedElement != null)
{
realizedElement.Measure(availableSize);
SetSize(realizedElement.DesiredSize, layoutItemWidth, LayoutItemHeight, availableSize, stretch, orientation, minRowSpacing, minColumnSpacing, maxItemsPerLine);
}
else
{
// Not realized by flowlayout, so do this now!
if (context.GetOrCreateElementAt(0, ElementRealizationOptions.ForceCreate) is { } firstElement)
{
firstElement.Measure(availableSize);
SetSize(firstElement.DesiredSize, layoutItemWidth, LayoutItemHeight, availableSize, stretch, orientation, minRowSpacing, minColumnSpacing, maxItemsPerLine);
context.RecycleElement(firstElement);
}
}
}
}