protected override void OnLayout(bool changed, int left, int top, int right, int bottom)
{
base.OnLayout(changed, left, top, right, bottom);
if (!changed)
{
return;
}
var startPos = _layoutManager.FindFirstCompletelyVisibleItemPosition();
var endPos = _layoutManager.FindLastCompletelyVisibleItemPosition();
int totalH = 0;
for (var i = startPos; i <= endPos; i++)
{
var child = _layoutManager.GetChildAt(i);
if (child == null)
{
return;
}
totalH += _layoutManager.GetChildAt(i).Height;
}
Element.VisibleContentHeight = Context.FromPixels(Math.Min(totalH, Control.Height));
}
/// <summary>
/// This method calculates the current scroll position and its offset to help new attached
/// recyclerView on window at that position and offset
/// </summary>
/// <seealso cref="GetScrollPosition()"/>
/// <seealso cref="GetScrollPositionOffset()"/>
private void RenewScrollPosition(RecyclerView recyclerView)
{
LinearLayoutManager layoutManager = (LinearLayoutManager)recyclerView.GetLayoutManager();
mScrollPosition = layoutManager.FindFirstCompletelyVisibleItemPosition();
// That means there is no completely visible Position.
if (mScrollPosition == -1)
{
mScrollPosition = layoutManager.FindFirstVisibleItemPosition();
// That means there is just a visible item on the screen
if (mScrollPosition == layoutManager.FindLastVisibleItemPosition())
{
}
else
{
// in this case we use the position which is the last & first visible item.
// That means there are 2 visible item on the screen. However, second one is not
// completely visible.
mScrollPosition = mScrollPosition + 1;
}
}
mScrollPositionOffset = layoutManager.FindViewByPosition(mScrollPosition).Left;
}
private int GetFirstCompletelyVisibleItemPosition()
{
return(mLayoutManager.FindFirstCompletelyVisibleItemPosition());
}