private void MeasureFocusedItem(int focusedIndex)
{
if (focusedIndex < 0 || focusedIndex >= SourceCount)
{
return;
}
if (focusedIndex >= FirstIndex && focusedIndex <= LastIndex)
{
return;
}
var focusedItem = Realize(focusedIndex);
if (focusedItem == null)
{
return;
}
if (focusedIndex < FirstIndex)
{
InsertItem(0, focusedItem);
Layout.MeasureChild(focusedItem, OrientedConstraint.Size);
OrientedLeadingSize = OrientedLeadingSize.StackSize(focusedItem.DesiredSize);
}
else
{
AddItem(focusedItem);
Layout.MeasureChild(focusedItem, OrientedConstraint.Size);
OrientedTrailingSize = OrientedTrailingSize.StackSize(focusedItem.DesiredSize);
}
}
private void MeasureLeading()
{
FirstIndex = (OffsetElementIndex - Layout.Panel.LeadingTrailingLimit).Clamp(0, SourceCount);
FirstVisibleIndex = OffsetElementIndex.Clamp(0, SourceCount);
var constraint = OrientedConstraint.Size;
var index = FirstIndex;
while (index < FirstVisibleIndex && index < SourceCount)
{
var element = Realize(index);
if (element == null)
{
index++;
continue;
}
AddItem(element);
Layout.MeasureChild(element, constraint);
OrientedLeadingSize = OrientedLeadingSize.StackSize(element.DesiredSize);
LeadingCacheCount++;
index++;
}
}
private void MeasureVisible()
{
var constraint = OrientedConstraint.Size;
var index = FirstVisibleIndex;
var realizedIndex = index;
while (OrientedAvailable.Direct > OrientedResult.Direct && index < SourceCount)
{
var element = Realize(index);
if (element == null)
{
index++;
continue;
}
realizedIndex = index;
AddItem(element);
Layout.MeasureChild(element, constraint);
OrientedResult = OrientedResult.StackSize(element.DesiredSize);
index++;
}
LastVisibleIndex = realizedIndex;
LastIndex = realizedIndex;
// Offset error. Move leading cache
while (OrientedAvailable.Direct > OrientedResult.Direct && FirstVisibleIndex > FirstIndex && FirstVisibleIndex > 0)
{
var element = Layout.UIElementInserter[FirstVisibleIndex - FirstIndex - 1];
var orientedSize = element.DesiredSize.AsOriented(Orientation);
var direct = OrientedResult.Direct + orientedSize.Direct;
if (direct > OrientedAvailable.Direct)
{
return;
}
OrientedResult = OrientedResult.ChangeDirect(direct);
OrientedLeadingSize = OrientedLeadingSize.ChangeDirect(OrientedLeadingSize.Direct - orientedSize.Direct);
FirstVisibleIndex--;
LeadingCacheCount--;
}
// Offset error. Measure beyond offset
if (OrientedAvailable.Direct > OrientedResult.Direct && FirstVisibleIndex > 0)
{
Debug.Assert(LeadingCacheCount == 0);
while (OrientedAvailable.Direct > OrientedResult.Direct && FirstVisibleIndex > 0)
{
var element = Realize(FirstVisibleIndex - 1);
if (element == null)
{
FirstVisibleIndex--;
continue;
}
InsertItem(0, element);
Layout.MeasureChild(element, constraint);
OrientedResult = OrientedResult.StackSize(element.DesiredSize);
FirstVisibleIndex--;
}
FirstIndex = FirstVisibleIndex;
// Remeasure leading cache
while (LeadingCacheCount < Layout.Panel.LeadingTrailingLimit && FirstIndex > 0)
{
var element = Realize(FirstIndex - 1);
if (element == null)
{
FirstIndex--;
continue;
}
InsertItem(0, element);
Layout.MeasureChild(element, constraint);
OrientedLeadingSize = OrientedLeadingSize.StackSize(element.DesiredSize);
FirstIndex--;
LeadingCacheCount++;
}
}
}