public override void OnItemsAdded(RecyclerView recyclerView, int positionStart, int itemCount)
{
_adapterChangeType = AdapterChangeType.Added;
_deferredLayout.Enqueue((recycler, state) => {
var viewByAdaptorPositionCopy = _viewByAdaptorPosition.ToArray();
_viewByAdaptorPosition.Clear();
foreach (KeyValuePair <int, AndroidView> pair in viewByAdaptorPositionCopy)
{
var view = pair.Value;
var position = pair.Key;
// position unchanged
if (position < positionStart)
{
_viewByAdaptorPosition[position] = view;
}
// position changed
else
{
_viewByAdaptorPosition[position + itemCount] = view;
}
}
if (_positionOrigin >= positionStart)
{
_positionOrigin += itemCount;
}
});
base.OnItemsAdded(recyclerView, positionStart, itemCount);
}
public override void OnItemsChanged(RecyclerView recyclerView)
{
_adapterChangeType = AdapterChangeType.Changed;
// low-fidelity change event; assume everything has changed. If adapter reports it has "stable IDs" then
// RecyclerView will attempt to synthesize high-fidelity change events: added, removed, moved, updated.
Reset(0);
RemoveAllViews();
}
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);
}
public override void OnItemsUpdated(RecyclerView recyclerView, int positionStart, int itemCount)
{
_adapterChangeType = AdapterChangeType.Updated;
// rebind rendered updated elements
_deferredLayout.Enqueue((recycler, state) => {
for (var i = 0; i < itemCount; i++)
{
var position = positionStart + i;
AndroidView view;
if (!_viewByAdaptorPosition.TryGetValue(position, out view))
{
continue;
}
recycler.BindViewToPosition(view, position);
}
});
base.OnItemsUpdated(recyclerView, positionStart, itemCount);
}
public override void OnItemsRemoved(RecyclerView recyclerView, int positionStart, int itemCount)
{
Assert(itemCount == MaxItemsRemoved);
_adapterChangeType = AdapterChangeType.Removed;
var positionEnd = positionStart + itemCount;
_deferredLayout.Enqueue((recycler, state) => {
if (state.ItemCount == 0)
{
throw new InvalidOperationException("Cannot delete all items.");
}
// re-map views to their new positions
var viewByAdaptorPositionCopy = _viewByAdaptorPosition.ToArray();
_viewByAdaptorPosition.Clear();
foreach (var pair in viewByAdaptorPositionCopy)
{
var view = pair.Value;
var position = pair.Key;
// position unchanged
if (position < positionStart)
{
_viewByAdaptorPosition[position] = view;
}
// position changed
else if (position >= positionEnd)
{
_viewByAdaptorPosition[position - itemCount] = view;
}
// removed
else
{
_viewByAdaptorPosition[-1] = view;
if (_visibleAdapterPosition.Contains(position))
{
_visibleAdapterPosition.Remove(position);
}
}
}
// if removed origin then shift origin to first removed position
if (_positionOrigin >= positionStart && _positionOrigin < positionEnd)
{
_positionOrigin = positionStart;
// if no items to right of removed origin then set origin to item prior to removed set
if (_positionOrigin >= state.ItemCount)
{
_positionOrigin = state.ItemCount - 1;
if (!_viewByAdaptorPosition.ContainsKey(_positionOrigin))
{
throw new InvalidOperationException(
"VirtualLayoutManager must add items to the left and right of the origin"
);
}
}
}
// if removed before origin then shift origin left
else if (_positionOrigin >= positionEnd)
{
_positionOrigin -= itemCount;
}
});
base.OnItemsRemoved(recyclerView, positionStart, itemCount);
}
public override void OnItemsMoved(RecyclerView recyclerView, int from, int toValue, int itemCount)
{
_adapterChangeType = AdapterChangeType.Moved;
base.OnItemsMoved(recyclerView, from, toValue, itemCount);
}
