public UICollectionViewCell CreateMeasurementCell(NSIndexPath indexPath)
{
if (ItemsView.ItemTemplate == null)
{
var frame = new CGRect(0, 0, ItemsViewLayout.EstimatedItemSize.Width, ItemsViewLayout.EstimatedItemSize.Height);
DefaultCell cell;
if (ItemsViewLayout.ScrollDirection == UICollectionViewScrollDirection.Horizontal)
{
cell = new HorizontalDefaultCell(frame);
}
else
{
cell = new VerticalDefaultCell(frame);
}
UpdateDefaultCell(cell, indexPath);
return(cell);
}
TemplatedCell templatedCell = CreateAppropriateCellForLayout();
UpdateTemplatedCell(templatedCell, indexPath);
// Keep this cell around, we can transfer the contents to the actual cell when the UICollectionView creates it
_measurementCells[ItemsSource[indexPath]] = templatedCell;
return(templatedCell);
}
protected virtual void UpdateTemplatedCell(TemplatedCell cell, NSIndexPath indexPath)
{
cell.ContentSizeChanged -= CellContentSizeChanged;
cell.LayoutAttributesChanged -= CellLayoutAttributesChanged;
var bindingContext = ItemsSource[indexPath];
// If we've already created a cell for this index path (for measurement), re-use the content
if (_measurementCells.TryGetValue(bindingContext, out TemplatedCell measurementCell))
{
_measurementCells.Remove(bindingContext);
measurementCell.ContentSizeChanged -= CellContentSizeChanged;
measurementCell.LayoutAttributesChanged -= CellLayoutAttributesChanged;
cell.UseContent(measurementCell);
}
else
{
cell.Bind(ItemsView.ItemTemplate, ItemsSource[indexPath], ItemsView);
}
cell.ContentSizeChanged += CellContentSizeChanged;
cell.LayoutAttributesChanged += CellLayoutAttributesChanged;
ItemsViewLayout.PrepareCellForLayout(cell);
}
internal void UseContent(TemplatedCell measurementCell)
{
// Copy all the content and values from the measurement cell
ConstrainedDimension = measurementCell.ConstrainedDimension;
ConstrainedSize = measurementCell.ConstrainedSize;
CurrentTemplate = measurementCell.CurrentTemplate;
_size = measurementCell._size;
SetRenderer(measurementCell.VisualElementRenderer);
}
void UpdateTemplatedSupplementaryView(TemplatedCell cell, NSString elementKind, NSIndexPath indexPath)
{
DataTemplate template = elementKind == UICollectionElementKindSectionKey.Header
? ItemsView.GroupHeaderTemplate
: ItemsView.GroupFooterTemplate;
var bindingContext = ItemsSource.Group(indexPath);
cell.Bind(template, bindingContext, ItemsView);
if (cell is ItemsViewCell)
{
cell.ConstrainTo(GetLayoutSpanCount() * ItemsViewLayout.ConstrainedDimension);
}
}
// These measurement methods are only necessary for iOS 10 and lower
CGSize MeasureTemplatedSupplementaryCell(NSString elementKind, nint section, NSString reuseId)
{
if (_measurementCellTemplated == null)
{
if (reuseId == HorizontalSupplementaryView.ReuseId)
{
_measurementCellTemplated = new HorizontalSupplementaryView(CGRect.Empty);
}
else if (reuseId == VerticalSupplementaryView.ReuseId)
{
_measurementCellTemplated = new VerticalSupplementaryView(CGRect.Empty);
}
}
if (_measurementCellTemplated == null)
{
return(CGSize.Empty);
}
UpdateTemplatedSupplementaryView(_measurementCellTemplated, elementKind, NSIndexPath.FromItemSection(0, section));
return(_measurementCellTemplated.Measure());
}