RecyclerView Adapter notifyDataSetChanged stops fancy animation

Question

I am building a component based on RecyclerView, allowing user to reorder items by drag and drop. Once I am on the DragListener side, I need the position it has in the adapter in order to perform correct move, but I only have access to the view. So here is what I am doing in the adapter view binding :

@Override public void onBindViewHolder(ViewHolder viewHolder, int position) {     Track track = mArray.get(position);     viewHolder.itemView.setTag(R.string.TAG_ITEM_POSITION, position); } 

Does it seem correct to you ? Because if I move an item like this :

public void move(int from, int to){     Track track = mArray.remove(from);     mArray.add(to, track);     notifyItemMoved(from, to); } 

then position tag is not correct anymore, and if I notifyDataSetChanged(), I lose the fancy animation. Any suggestion ?

Answer 1

There is a way to preserve fancy animations with just notifyDataSetChanged()

1. You need to make your own GridLayoutManager with overriden supportsPredictiveItemAnimations() method returning true;

2. You need to mAdapter.setHasStableIds(true)

3. The part I find tricky is you need to override you adapter's getItemId() method. It should return value that is truly unique and not a direct function of position. Something like mItems.get(position).hashCode()

Worked perfectly fine in my case - beautiful animations for adding, removing and moving items only using notifyDataSetChanged()

Answer 2

No, it is wrong. First of all, you cannot reference to the position passed to the onBindViewHolder after that method returns. RecyclerView will not rebind a view when its position changes (due to items moving etc).

Instead, you can use ViewHolder#getPosition() which will return you the updated position.

If you fix that, your move code should work & provide nice animations.

Calling notifyDataSetChanged will prevent predictive animations so avoid it as long as you can. See documentation for details.

Edit (from comment): to get position from the outside, get child view holder from recyclerview and then get position from the vh. See RecyclerView api for details