public override void InvalidateLayout(UICollectionViewLayoutInvalidationContext context)
{
base.InvalidateLayout(context);
if (CollectionView != null)
{
var currentCollectionViewSize = CollectionView.Bounds.Size;
if (!currentCollectionViewSize.Equals(lastCollectionViewSize))
{
ConfigureInset();
lastCollectionViewSize = currentCollectionViewSize;
}
}
}
public override UICollectionViewLayoutInvalidationContext GetInvalidationContext(UICollectionViewLayoutAttributes preferredAttributes, UICollectionViewLayoutAttributes originalAttributes)
{
if (Forms.IsiOS11OrNewer)
{
return(base.GetInvalidationContext(preferredAttributes, originalAttributes));
}
var indexPath = preferredAttributes.IndexPath;
try
{
UICollectionViewLayoutInvalidationContext invalidationContext =
base.GetInvalidationContext(preferredAttributes, originalAttributes);
// Ensure that if this invalidation was triggered by header/footer changes, the header/footer
// are being invalidated
if (preferredAttributes.RepresentedElementKind == UICollectionElementKindSectionKey.Header)
{
invalidationContext.InvalidateSupplementaryElements(UICollectionElementKindSectionKey.Header,
new[] { indexPath });
}
else if (preferredAttributes.RepresentedElementKind == UICollectionElementKindSectionKey.Footer)
{
invalidationContext.InvalidateSupplementaryElements(UICollectionElementKindSectionKey.Footer,
new[] { indexPath });
}
return(invalidationContext);
}
catch (MonoTouchException)
{
// This happens on iOS 10 if we have any empty groups in our ItemsSource. Catching here and
// returning a UICollectionViewFlowLayoutInvalidationContext means that the application does not
// crash, though any group headers/footers will initially draw in the wrong location. It's possible to
// work around this problem by forcing a full layout update after the headers/footers have been
// drawn in the wrong places
}
return(new UICollectionViewFlowLayoutInvalidationContext());
}
