TransitionManager doesn't animate color change

Question

I've followed Nick Butcher's Material Improvements I/O 2016 talk, and at about 6:00, he starts talking about animating list items. I've implemented the feature exactly as he was doing it, and the bound changes animate correctly, but color changes don't animate, despite him explicitly saying they would:

This is what the code looks like:

This is the relevant part of the RecyclerView.Adapter class:

override fun onBindViewHolder(holder: ViewHolder, position: Int) {
    val item: Pair<String, String> = items[position]

    holder.title.text = item.first
    holder.subtitle.text = item.second

    val isExpanded = position == expandedPosition
    holder.subtitle.visibility = if (isExpanded) View.VISIBLE else View.GONE
    holder.itemView.isActivated = isExpanded
    holder.itemView.setOnClickListener {
        expandedPosition = if (isExpanded) -1 else position
        TransitionManager.beginDelayedTransition(recyclerView)
        notifyDataSetChanged()
    }
}

This is the layout I'm using for the items. ConstraintLayout is kind of overkill for the current layout setup, but I reduced the layout to create a minimal example.

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    tools:context=".MainActivity"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@drawable/item_background"
    android:stateListAnimator="@animator/item_elevation"
    android:padding="8dp">

    <TextView
        android:id="@+id/title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="24sp"
        tools:text="Title 1"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"/>

    <TextView
        android:id="@+id/subtitle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        tools:text="Subtitle 1"
        app:layout_constraintTop_toBottomOf="@id/title"
        app:layout_constraintStart_toStartOf="parent"
        />

</android.support.constraint.ConstraintLayout>

And this is the background I'm using for the item layout:

<selector xmlns:android="http://schemas.android.com/apk/res/android"
    android:enterFadeDuration="@android:integer/config_mediumAnimTime"
    android:exitFadeDuration="@android:integer/config_mediumAnimTime">

    <item android:state_activated="true"
        android:drawable="@color/colorAccent" />

    <item android:drawable="@color/colorPrimaryDark" />

</selector>

Answer 1

Make sure that you have stable ids for your dataset and call Recycler.Adapter#setHasStableIds(true). See setHasStableIds().

You will also need to override getItemId() in the adapter to return a stable id. Also see notifyDataSetChanged for a short discussion of stable ids.

RecyclerView will attempt to synthesize visible structural change events for adapters that report that they have stable IDs when this method is used. This can help for the purposes of animation and visual object persistence but individual item views will still need to be rebound and relaid out.

Here is an demonstration with stable ids set to false:

and with stable ids set to true. I have make the transition time very long on the color change so it would be apparent.

RecyclerViewAdapter.java

This is the adapter used in the demo. TransitionManager.beginDelayedTransition(mRecyclerView) has been removed to let RecyclerView better handle the animation.

class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    RecyclerViewAdapter() {
    }

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view;
        view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_layout, parent, false);
        return new ItemViewHolder(view);
    }

    private int mExpandedPosition = RecyclerView.NO_POSITION;

    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
        final ItemViewHolder vh = (ItemViewHolder) holder;
        final TextView subTitle = vh.mSubTitle;

        vh.mTitle.setText(titleForPosition(position));
        subTitle.setText(subTitleForPosition(position));

        final boolean isExpanded = position == mExpandedPosition;

        subTitle.setVisibility((isExpanded) ? View.VISIBLE : View.GONE);
        holder.itemView.setActivated(isExpanded);
        holder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mExpandedPosition = isExpanded ? RecyclerView.NO_POSITION : vh.getAdapterPosition();
                notifyDataSetChanged();
            }
        });
    }

    private String titleForPosition(int position) {
        return "Title " + position;
    }

    private String subTitleForPosition(int position) {
        return "Subtitle " + position;
    }

    @Override
    public int getItemCount() {
        return 5;
    }

    @Override
    public long getItemId(int position) {
        return titleForPosition(position).hashCode();
    }

    static class ItemViewHolder extends RecyclerView.ViewHolder {
        private final TextView mTitle;
        private final TextView mSubTitle;

        ItemViewHolder(View itemView) {
            super(itemView);
            mTitle = itemView.findViewById(R.id.title);
            mSubTitle = itemView.findViewById(R.id.subtitle);
        }
    }

    @SuppressWarnings("unused")
    private final static String TAG = "RecyclerViewAdapter";
}