/// <summary>
/// Get the index of the next item that has not yet been materialized in the nominated fill direction. Returns null if there are no more available items in the source.
/// </summary>
protected Uno.UI.IndexPath?GetNextUnmaterializedItem(GeneratorDirection fillDirection, Uno.UI.IndexPath? currentMaterializedItem)
{
return(XamlParent?.GetNextItemIndex(currentMaterializedItem, fillDirection == GeneratorDirection.Forward ? 1 : -1));
}
protected override Line CreateLine(GeneratorDirection direction,
int extentOffset,
int breadthOffset,
int availableBreadth,
RecyclerView.Recycler recycler,
RecyclerView.State state,
IndexPath nextVisibleItem,
bool isNewGroup
)
{
var itemsInLine = ResolveMaximumItemsInLine(availableBreadth);
var firstItemInLine = nextVisibleItem;
//Find first item in line, since the item we are passed is the last
if (direction == GeneratorDirection.Backward)
{
// We are recreating the last line of the group - it may be truncated (if the total items are not an even multiple
// of the items-per-line).
if (isNewGroup)
{
itemsInLine = XamlParent.GetItemsOnLastLine(firstItemInLine.Section, itemsInLine);
}
for (int i = 0; i < itemsInLine - 1; i++)
{
firstItemInLine = GetNextUnmaterializedItem(GeneratorDirection.Backward, firstItemInLine).Value;
var isCorrectGroup = firstItemInLine.Section == nextVisibleItem.Section;
if (!isCorrectGroup)
{
//TODO: fix bug that makes this happen (#47229)
}
Debug.Assert(isCorrectGroup, GetAssertMessage("First item should not be from a different group"));
}
}
IndexPath lastItemInLine = firstItemInLine;
IndexPath?currentItem = firstItemInLine;
var availableWidth = ResolveAvailableWidth(availableBreadth);
var availableHeight = ResolveAvailableHeight(availableBreadth);
int usedBreadth = 0;
for (int i = 0; i < itemsInLine; i++)
{
var view = recycler.GetViewForPosition(GetFlatItemIndex(currentItem.Value), state);
if (!(view is SelectorItem))
{
throw new InvalidOperationException($"Expected {nameof(SelectorItem)} but received {view?.GetType().ToString() ?? "<null>"}");
}
//Add view before we measure it, this ensures that DP inheritances are correctly applied
AddView(view, direction);
var slotSize = new Windows.Foundation.Size(availableWidth, availableHeight).PhysicalToLogicalPixels();
var measuredSize = _layouter.MeasureChild(view, slotSize);
var physicalMeasuredSize = measuredSize.LogicalToPhysicalPixels();
var measuredWidth = (int)physicalMeasuredSize.Width;
var measuredHeight = (int)physicalMeasuredSize.Height;
if (_implicitItemWidth == null)
{
//Set these values to dimensions of first materialised item
_implicitItemWidth = measuredWidth;
_implicitItemHeight = measuredHeight;
// When an item dimension is not fixed, we need to arrange based on the measured size,
// otherwise the arrange will be passed a dimension that is too large and the first
// few items will not be visible
if (double.IsNaN(ItemWidth))
{
slotSize.Width = ViewHelper.PhysicalToLogicalPixels(_implicitItemWidth.Value);
}
if (double.IsNaN(ItemHeight))
{
slotSize.Height = ViewHelper.PhysicalToLogicalPixels(_implicitItemHeight.Value);
}
availableWidth = ResolveAvailableWidth(availableBreadth);
availableHeight = ResolveAvailableHeight(availableBreadth);
itemsInLine = ResolveMaximumItemsInLine(availableBreadth);
}
LayoutChild(view,
GeneratorDirection.Forward,
//We always lay out view 'top down' so that it is aligned correctly if its height is less than the line height
direction == GeneratorDirection.Forward ? extentOffset : extentOffset - ResolveItemExtent().Value,
breadthOffset + usedBreadth,
slotSize
);
usedBreadth += ResolveItemBreadth().Value;
lastItemInLine = currentItem.Value;
currentItem = GetNextUnmaterializedItem(GeneratorDirection.Forward, currentItem);
if (currentItem == null || currentItem.Value.Section != firstItemInLine.Section)
{
itemsInLine = i + 1;
break;
}
}
return(new Line
{
NumberOfViews = itemsInLine,
Extent = ResolveItemExtent().Value,
Breadth = usedBreadth,
FirstItem = firstItemInLine,
LastItem = lastItemInLine
});
}