public void OnItemsSourceChanged(object _, NotifyCollectionChangedEventArgs args)
{
// Note: For items that have been removed, the index will not be touched. It will hold
// the old index before it was removed. It is not valid anymore.
switch (args.Action)
{
case NotifyCollectionChangedAction.Add:
{
var newIndex = args.NewStartingIndex;
var newCount = args.NewItems.Count;
EnsureFirstLastRealizedIndices();
if (newIndex <= m_lastRealizedElementIndexHeldByLayout)
{
m_lastRealizedElementIndexHeldByLayout += newCount;
var children = m_owner.Children;
var childCount = children.Count;
for (int i = 0; i < childCount; ++i)
{
var element = children[i];
var virtInfo = ItemsRepeater.GetVirtualizationInfo(element);
var dataIndex = virtInfo.Index;
if (virtInfo.IsRealized && dataIndex >= newIndex)
{
UpdateElementIndex(element, virtInfo, dataIndex + newCount);
}
}
}
else
{
// Indices held by layout are not affected
// We could still have items in the pinned elements that need updates. This is usually a very small vector.
for (int i = 0; i < m_pinnedPool.Count; ++i)
{
var elementInfo = m_pinnedPool[i];
var virtInfo = elementInfo.VirtualizationInfo;
var dataIndex = virtInfo.Index;
if (virtInfo.IsRealized && dataIndex >= newIndex)
{
var element = elementInfo.PinnedElement;
UpdateElementIndex(element, virtInfo, dataIndex + newCount);
}
}
}
break;
}
case NotifyCollectionChangedAction.Replace:
{
// Requirement: oldStartIndex == newStartIndex. It is not a replace if this is not true.
// Two cases here
// case 1: oldCount == newCount
// indices are not affected. nothing to do here.
// case 2: oldCount != newCount
// Replaced with less or more items. This is like an insert or remove
// depending on the counts.
var oldStartIndex = args.OldStartingIndex;
var newStartingIndex = args.NewStartingIndex;
var oldCount = (int)(args.OldItems.Count);
var newCount = (int)(args.NewItems.Count);
if (oldStartIndex != newStartingIndex)
{
throw new InvalidOperationException("Replace is only allowed with OldStartingIndex equals to NewStartingIndex.");
}
if (oldCount == 0)
{
throw new InvalidOperationException("Replace notification with args.OldItemsCount value of 0 is not allowed. Use Insert action instead.");
}
if (newCount == 0)
{
throw new InvalidOperationException("Replace notification with args.NewItemCount value of 0 is not allowed. Use Remove action instead.");
}
int countChange = newCount - oldCount;
if (countChange != 0)
{
// countChange > 0 : countChange items were added
// countChange < 0 : -countChange items were removed
var children = m_owner.Children;
for (int i = 0; i < children.Count; ++i)
{
var element = children[i];
var virtInfo = ItemsRepeater.GetVirtualizationInfo(element);
var dataIndex = virtInfo.Index;
if (virtInfo.IsRealized)
{
if (dataIndex >= oldStartIndex + oldCount)
{
UpdateElementIndex(element, virtInfo, dataIndex + countChange);
}
}
}
EnsureFirstLastRealizedIndices();
m_lastRealizedElementIndexHeldByLayout += countChange;
}
break;
}
case NotifyCollectionChangedAction.Remove:
{
var oldStartIndex = args.OldStartingIndex;
var oldCount = (int)(args.OldItems.Count);
var children = m_owner.Children;
for (int i = 0; i < children.Count; ++i)
{
var element = children[i];
var virtInfo = ItemsRepeater.GetVirtualizationInfo(element);
var dataIndex = virtInfo.Index;
if (virtInfo.IsRealized)
{
if (virtInfo.AutoRecycleCandidate && oldStartIndex <= dataIndex && dataIndex < oldStartIndex + oldCount)
{
// If we are doing the mapping, remove the element who's data was removed.
m_owner.ClearElementImpl(element);
}
else if (dataIndex >= (oldStartIndex + oldCount))
{
UpdateElementIndex(element, virtInfo, dataIndex - oldCount);
}
}
}
InvalidateRealizedIndicesHeldByLayout();
break;
}
case NotifyCollectionChangedAction.Reset:
// If we get multiple resets back to back before
// running layout, we dont have to clear all the elements again.
if (!m_isDataSourceStableResetPending)
{
#if DEBUG
// There should be no elements in the reset pool at this time.
MUX_ASSERT(m_resetPool.IsEmpty);
#endif
if (m_owner.ItemsSourceView.HasKeyIndexMapping)
{
m_isDataSourceStableResetPending = true;
}
// Walk through all the elements and make sure they are cleared, they will go into
// the stable id reset pool.
var children = m_owner.Children;
for (int i = 0; i < children.Count; ++i)
{
var element = children[i];
var virtInfo = ItemsRepeater.GetVirtualizationInfo(element);
if (virtInfo.IsRealized && virtInfo.AutoRecycleCandidate)
{
m_owner.ClearElementImpl(element);
}
}
}
InvalidateRealizedIndicesHeldByLayout();
break;
}
}
