public override UICollectionViewLayoutInvalidationContext GetInvalidationContext(UICollectionViewLayoutAttributes preferredAttributes, UICollectionViewLayoutAttributes originalAttributes)
{
if (preferredAttributes.RepresentedElementKind != UICollectionElementKindSectionKey.Header &&
preferredAttributes.RepresentedElementKind != UICollectionElementKindSectionKey.Footer)
{
return(base.GetInvalidationContext(preferredAttributes, originalAttributes));
}
// Ensure that if this invalidation was triggered by header/footer changes, the header/footer are being invalidated
UICollectionViewFlowLayoutInvalidationContext invalidationContext = new UICollectionViewFlowLayoutInvalidationContext();
var indexPath = preferredAttributes.IndexPath;
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);
// On iOS 10 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
}
public override UICollectionViewLayoutInvalidationContext GetInvalidationContext(UICollectionViewLayoutAttributes preferredAttributes, UICollectionViewLayoutAttributes originalAttributes)
{
if (preferredAttributes.RepresentedElementKind != UICollectionElementKindSectionKey.Header &&
preferredAttributes.RepresentedElementKind != UICollectionElementKindSectionKey.Footer)
{
if (Forms.IsiOS12OrNewer)
{
return(base.GetInvalidationContext(preferredAttributes, originalAttributes));
}
try
{
// We only have to do this on older iOS versions; sometimes when removing a cell that's right at the edge
// of the viewport we'll run into a race condition where the invalidation context will have the removed
// indexpath. And then things crash. So
var defaultContext = base.GetInvalidationContext(preferredAttributes, originalAttributes);
return(defaultContext);
}
catch (MonoTouchException ex) when(ex.Name == "NSRangeException")
{
Forms.MauiContext?.CreateLogger <ItemsViewLayout>()?.LogWarning(ex, "NSRangeExceptiond");
}
UICollectionViewFlowLayoutInvalidationContext context = new UICollectionViewFlowLayoutInvalidationContext();
return(context);
}
// Ensure that if this invalidation was triggered by header/footer changes, the header/footer are being invalidated
UICollectionViewFlowLayoutInvalidationContext invalidationContext = new UICollectionViewFlowLayoutInvalidationContext();
var indexPath = preferredAttributes.IndexPath;
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);
}
public override UICollectionViewLayoutInvalidationContext GetInvalidationContext(UICollectionViewLayoutAttributes preferredAttributes, UICollectionViewLayoutAttributes originalAttributes)
{
if (preferredAttributes.RepresentedElementKind != UICollectionElementKindSectionKey.Header &&
preferredAttributes.RepresentedElementKind != UICollectionElementKindSectionKey.Footer)
{
return(base.GetInvalidationContext(preferredAttributes, originalAttributes));
}
// Ensure that if this invalidation was triggered by header/footer changes, the header/footer are being invalidated
UICollectionViewFlowLayoutInvalidationContext invalidationContext = new UICollectionViewFlowLayoutInvalidationContext();
var indexPath = preferredAttributes.IndexPath;
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);
}