Drop event listener about android-itemtouchhelper-demo HOT 8 CLOSED

public class SimpleItemTouchHelperCallback extends ItemTouchHelper.Callback {

private Integer mFrom = null;
private Integer mTo = null;

....

@Override
public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder source, RecyclerView.ViewHolder target) {
    if (source.getItemViewType() != target.getItemViewType()) {
        return false;
    }

    // remember FIRST from position
    if (mFrom == null)
        mFrom = source.getAdapterPosition();
    mTo = target.getAdapterPosition();

    // Notify the adapter of the move
    mAdapter.onItemMove(source.getAdapterPosition(), target.getAdapterPosition());
    return true;
}

@Override
public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
    super.clearView(recyclerView, viewHolder);

    viewHolder.itemView.setAlpha(ALPHA_FULL);

    if (viewHolder instanceof ItemTouchHelperViewHolder) {
        // Tell the view holder it's time to restore the idle state
        ItemTouchHelperViewHolder itemViewHolder = (ItemTouchHelperViewHolder) viewHolder;
        itemViewHolder.onItemClear();
    }

    if (mFrom != null && mTo != null)
        mAdapter.onDrop(mFrom, mTo);

    // clear saved positions
    mFrom = mTo = null;
}
}