protected virtual void BoundsSizeChanged()
{
//We are changing orientation and we need to tell our layout
//to update based on new size constrains
ItemsViewLayout.ConstrainTo(CollectionView.Bounds.Size);
//We call ReloadData so our VisibleCells also update their size
CollectionView.ReloadData();
}
void CheckForEmptySource()
{
var wasEmpty = _isEmpty;
_isEmpty = ItemsSource.ItemCount == 0;
if (wasEmpty != _isEmpty)
{
UpdateEmptyViewVisibility(_isEmpty);
}
if (wasEmpty && !_isEmpty)
{
// If we're going from empty to having stuff, it's possible that we've never actually measured
// a prototype cell and our itemSize or estimatedItemSize are wrong/unset
// So trigger a constraint update; if we need a measurement, that will make it happen
ItemsViewLayout.ConstrainTo(CollectionView.Bounds.Size);
}
}
public override void ViewWillLayoutSubviews()
{
base.ViewWillLayoutSubviews();
// We can't set this constraint up on ViewDidLoad, because Forms does other stuff that resizes the view
// and we end up with massive layout errors. And View[Will/Did]Appear do not fire for this controller
// reliably. So until one of those options is cleared up, we set this flag so that the initial constraints
// are set up the first time this method is called.
if (!_initialConstraintsSet)
{
_size = CollectionView.Bounds.Size;
ItemsViewLayout.ConstrainTo(_size);
UpdateEmptyView();
_initialConstraintsSet = true;
}
else
{
LayoutEmptyView();
}
}
public void UpdateLayout(ItemsViewLayout newLayout)
{
// Ignore calls to this method if the new layout is the same as the old one
if (CollectionView.CollectionViewLayout == newLayout)
{
return;
}
ItemsViewLayout = newLayout;
ItemsViewLayout.GetPrototype = GetPrototype;
Delegator = CreateDelegator();
CollectionView.Delegate = Delegator;
// Make sure the new layout is sized properly
ItemsViewLayout.ConstrainTo(CollectionView.Bounds.Size);
CollectionView.SetCollectionViewLayout(ItemsViewLayout, false);
// Reload the data so the currently visible cells get laid out according to the new layout
CollectionView.ReloadData();
}