protected override (int First, int Center, int Last) GetVisibleItemsIndex(RecyclerView recyclerView)
{
var firstVisibleItemIndex = -1;
var lastVisibleItemIndex = -1;
var centerItemIndex = -1;
if (recyclerView.GetLayoutManager() is LinearLayoutManager linearLayoutManager)
{
var firstView = recyclerView.FindViewHolderForAdapterPosition(linearLayoutManager.FindFirstVisibleItemPosition());
var lastView = recyclerView.FindViewHolderForAdapterPosition(linearLayoutManager.FindLastVisibleItemPosition());
var centerView = recyclerView.GetCenteredView();
firstVisibleItemIndex = GetIndexFromTemplatedCell(firstView?.ItemView);
lastVisibleItemIndex = GetIndexFromTemplatedCell(lastView?.ItemView);
centerItemIndex = GetIndexFromTemplatedCell(centerView);
}
return(firstVisibleItemIndex, centerItemIndex, lastVisibleItemIndex);
}
public int GetGoToIndex(RecyclerView recyclerView, int carouselPosition, int newPosition)
{
if (!(recyclerView.GetLayoutManager() is LinearLayoutManager linearLayoutManager))
{
return(-1);
}
var currentCarouselPosition = carouselPosition;
var itemSourceCount = _itemsSource.Count;
var diffToStart = currentCarouselPosition + (itemSourceCount - newPosition);
var diffToEnd = itemSourceCount - currentCarouselPosition + newPosition;
var centerView = recyclerView.GetCenteredView();
if (centerView == null)
{
return(-1);
}
var centerPosition = linearLayoutManager.GetPosition(centerView);
var increment = currentCarouselPosition - newPosition;
var incrementAbs = System.Math.Abs(increment);
int goToPosition;
if (diffToStart < incrementAbs)
{
goToPosition = centerPosition - diffToStart;
}
else if (diffToEnd < incrementAbs)
{
goToPosition = centerPosition + diffToEnd;
}
else
{
goToPosition = centerPosition - increment;
}
return(goToPosition);
}