Bad performance when use RecyclerView inside NestedScrollView

Question

I'm developing a search contact feature, in that screen, there is a RecyclerView inside NestedScrolView (fillViewport = true). Screen design: (This design is accepted by customer, I can't change it)

After loading all contacts of current device into an ArrayList, the search results are filtered from this array.
There is several cases that make the app very laggy:
1. When user type an input that have no result, then user clear search, I have to show all results again. The NestedScrollView has to render UI for all items of RecyclerView (for example: 300 items).
2. When the quantity of results has many changes (for example, from 1 to 300 items). The NestedScrollView has to render UI for a lot of items of RecyclerView

I know this design breaks recycling technique of RecyclerView, but I can't change it.
What I tried:

recyclerView.setNestedScrollingEnabled(false);

In AndroidManifest:

android:windowSoftInputMode="adjustNothing"

The adapter:

public class RecyclerContactAdapter extends RecyclerView.Adapter<RecyclerContactAdapter.ViewHolder> {

    private List<MobileContact> contacts;
    private Context context;

    public RecyclerContactAdapter() {
        contacts = new ArrayList<>();
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        this.context = parent.getContext();
        View view = LayoutInflater.from(context)
                .inflate(R.layout.item_recycler_contact, parent, false);

        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        //set data for view
    }

    @Override
    public int getItemCount() {
        return contacts.size();
    }

    protected class ViewHolder extends RecyclerView.ViewHolder {
        private TextView tvAlphabetHeader;
        private CircleImageView civAvatar;
        private TextView tvContactName;
        private TextView tvStatus;
        private CheckBox cbInvited;
        private RelativeLayout rlAlphabetHeader;
        private RelativeLayout rlContainer;

        protected ViewHolder(View itemView) {
            super(itemView);
            tvAlphabetHeader = itemView.findViewById(R.id.item_recycler_contact_tv_alphabet_header);
            civAvatar = itemView.findViewById(R.id.item_recycler_contact_civ_avatar);
            tvContactName = itemView.findViewById(R.id.item_recycler_contact_tv_name);
            tvStatus = itemView.findViewById(R.id.item_recycler_contact_tv_status);
            cbInvited = itemView.findViewById(R.id.item_recycler_contact_cb_contact);
            rlAlphabetHeader =  itemView.findViewById(R.id.item_recycler_contact_rl_alphabet);
            rlContainer = itemView.findViewById(R.id.item_recycler_contact_rl_contact);
        }
    }

    public void addAll(List<MobileContact> mobileContacts) {
        this.contacts.clear();
        this.contacts.addAll(mobileContacts);
        notifyDataSetChanged();
    }

    public void add(MobileContact mobileContact) {
        this.contacts.add(mobileContact);
    }

    public List<MobileContact> getContacts() {
        return this.contacts;
    }

}

Answer 1

You are using RecyclerView incorrectly. Instead of putting your RecyclerView inside NestedScrollView put your "Header" and "Search box" inside RecyclerView as different view types.

This answer is a good example.