public override int ScrollVerticallyBy(int dy, Recycler recycler, State state)
{
var delta = new IntVector(0, dy);
ScrollBy(ref delta, recycler, state);
return(delta.Y);
}
public override int ScrollHorizontallyBy(int dx, Recycler recycler, State state)
{
var delta = new IntVector(dx, 0);
ScrollBy(ref delta, recycler, state);
return(delta.X);
}
public override void OnLayoutChildren(Android.Support.V7.Widget.RecyclerView.Recycler recycler,
Android.Support.V7.Widget.RecyclerView.State state)
{
try
{
base.OnLayoutChildren(recycler, state);
}
catch (IndexOutOfBoundsException e)
{
Mvx.Warning(
"Workaround of issue - https://code.google.com/p/android/issues/detail?id=77846#c1 - IndexOutOfBoundsException " +
e.Message);
}
}
void ScrollBy(ref IntVector delta, Recycler recycler, State state)
{
_adapterChangeType = default(AdapterChangeType);
delta = Viewport.BoundTranslation(
delta: delta,
bound: _virtualLayout.GetBounds(_positionOrigin, state)
);
_locationOffset += delta;
_samples.Insert(0, delta);
_samples.RemoveAt(_samples.Count - 1);
OffsetChildren(delta);
OnLayoutChildren(recycler, state);
}
internal void DetachAndScrap(Recycler recycler)
{
_layout.DetachAndScrapView(_view, recycler);
}
public override void OnLayoutChildren(Recycler recycler, State state)
{
var adapterChangeType = _adapterChangeType;
if (state.IsPreLayout)
{
adapterChangeType = default(AdapterChangeType);
}
// adapter updates
if (!state.IsPreLayout)
{
while (_deferredLayout.Count > 0)
{
_deferredLayout.Dequeue()(recycler, state);
}
}
// get visible items
var positions = _virtualLayout.GetPositions(
positionOrigin: _positionOrigin,
itemCount: state.ItemCount,
viewport: Viewport
).ToRange();
// disappearing
var disappearing = _viewByAdaptorPosition.Keys.Except(positions).ToList();
// defer cleanup of displaced items and lay them out off-screen so they animate off-screen
if (adapterChangeType == AdapterChangeType.Added)
{
positions = positions.Concat(disappearing).OrderBy(o => o).ToArray();
disappearing.Clear();
}
// recycle
foreach (var position in disappearing)
{
var view = _viewByAdaptorPosition[position];
// remove
_viewByAdaptorPosition.Remove(position);
// scrap
new DecoratedView(this, view).DetachAndScrap(recycler);
}
// TODO: Generalize
if (adapterChangeType == AdapterChangeType.Removed && _positionOrigin == state.ItemCount - 1)
{
var vlayout = _virtualLayout.LayoutItem(_positionOrigin, _positionOrigin);
_locationOffset = new IntVector(vlayout.Width - Width, _locationOffset.Y);
}
_visibleAdapterPosition.Clear();
var nextLocationOffset = new IntPoint(int.MaxValue, int.MaxValue);
var nextPositionOrigin = int.MaxValue;
foreach (var position in positions)
{
// attach
AndroidView view;
if (!_viewByAdaptorPosition.TryGetValue(position, out view))
{
AddView(_viewByAdaptorPosition[position] = view = recycler.GetViewForPosition(position));
}
// layout
var decoratedView = new DecoratedView(this, view);
var layout = _virtualLayout.LayoutItem(_positionOrigin, position);
var physicalLayout = layout - _locationOffset;
decoratedView.Layout(physicalLayout);
var isVisible = Viewport.IntersectsWith(layout);
if (isVisible)
{
_visibleAdapterPosition.Add(position);
}
// update offsets
if (isVisible && position < nextPositionOrigin)
{
nextLocationOffset = layout.Location;
nextPositionOrigin = position;
}
}
// update origin
if (nextPositionOrigin != int.MaxValue)
{
_positionOrigin = nextPositionOrigin;
_locationOffset -= (IntVector)nextLocationOffset;
}
// scrapped views not re-attached must be recycled (why isn't this done by Android, I dunno)
foreach (var viewHolder in recycler.ScrapList.ToArray())
{
recycler.RecycleView(viewHolder.ItemView);
}
}
