How to sync scrolling first-positions of 2 RecyclerViews?

Question

Background

I have 2 RecyclerView instances. One is horizontal, and the second is vertical.

They both show the same data and have the same amount of items,

Answer 1

Another simple solution working fine in my device

Variable

RecyclerView horizontalRecyclerView, verticalRecyclerView;
LinearLayoutManager horizontalLayoutManager, verticalLayoutManager;

ArrayList arrayList = new ArrayList<>();
ArrayList arrayList2 = new ArrayList<>();

RecyclerView code

horizontalRecyclerView = findViewById(R.id.horizontalRc);
verticalRecyclerView = findViewById(R.id.verticalRc);

horizontalRecyclerView.setHasFixedSize(true);
verticalRecyclerView.setHasFixedSize(true);

horizontalLayoutManager = new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false);
verticalLayoutManager = new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false);

horizontalRecyclerView.setLayoutManager(horizontalLayoutManager);
verticalRecyclerView.setLayoutManager(verticalLayoutManager);

for (int i = 0; i < 50; i++) {
     arrayList.add("" + i);
     arrayList2.add("" + i);
 }

 MyDataAdapter horizontalAdapter = new MyDataAdapter(this, arrayList);
 MyDataAdapter verticalAdapter = new MyDataAdapter(this, arrayList2);

 horizontalRecyclerView.setAdapter(horizontalAdapter);
 verticalRecyclerView.setAdapter(verticalAdapter);

logic inside RecyclerView.addOnScrollListener

 horizontalRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);

                int pos = horizontalLayoutManager.findFirstCompletelyVisibleItemPosition();
                verticalLayoutManager.scrollToPositionWithOffset(pos, 20);

            }

        });


        verticalRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {

            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);

                int pos = verticalLayoutManager.findFirstCompletelyVisibleItemPosition();
                horizontalLayoutManager.scrollToPositionWithOffset(pos, 20);


            }
        });

Hope it help some one

WHOLE Code

public class Main4Activity extends AppCompatActivity {

    RecyclerView horizontalRecyclerView, verticalRecyclerView;
    LinearLayoutManager horizontalLayoutManager, verticalLayoutManager;

    ArrayList arrayList = new ArrayList<>();
    ArrayList arrayList2 = new ArrayList<>();

    boolean isVertical = true, isHorizontal = true;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main4);


        horizontalRecyclerView = findViewById(R.id.horizontalRc);
        verticalRecyclerView = findViewById(R.id.verticalRc);

        horizontalRecyclerView.setHasFixedSize(true);
        verticalRecyclerView.setHasFixedSize(true);

        horizontalLayoutManager = new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false);
        verticalLayoutManager = new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false);

        horizontalRecyclerView.setLayoutManager(horizontalLayoutManager);
        verticalRecyclerView.setLayoutManager(verticalLayoutManager);

        for (int i = 0; i < 50; i++) {
            arrayList.add("" + i);
            arrayList2.add("" + i);
        }

        MyDataAdapter horizontalAdapter = new MyDataAdapter(this, arrayList);
        MyDataAdapter verticalAdapter = new MyDataAdapter(this, arrayList2);

        horizontalRecyclerView.setAdapter(horizontalAdapter);
        verticalRecyclerView.setAdapter(verticalAdapter);

        horizontalRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);

                int pos = horizontalLayoutManager.findFirstCompletelyVisibleItemPosition();
                verticalLayoutManager.scrollToPositionWithOffset(pos, 20);


            }

        });


        verticalRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {

            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);

                int pos = verticalLayoutManager.findFirstCompletelyVisibleItemPosition();
                horizontalLayoutManager.scrollToPositionWithOffset(pos, 20);


            }
        });



       /* horizontalRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);

                int pos = horizontalLayoutManager.findFirstCompletelyVisibleItemPosition();
                verticalLayoutManager.scrollToPositionWithOffset(pos, 20);

                *//*if (isHorizontal) {
                    int pos = horizontalLayoutManager.findFirstCompletelyVisibleItemPosition();
                    verticalLayoutManager.scrollToPositionWithOffset(pos, 20);
                    Log.e("isHorizontal", "TRUE");
                    isVertical = false;
                } else {
                    isHorizontal = true;
                }*//*

            }

           *//* @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);
                isVertical = true;
            }*//*
        });


        verticalRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {

            *//* @Override
             public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                 super.onScrollStateChanged(recyclerView, newState);
                 isHorizontal = true;
             }
 *//*
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);

                int pos = verticalLayoutManager.findFirstCompletelyVisibleItemPosition();
                horizontalLayoutManager.scrollToPositionWithOffset(pos, 20);

               *//* if (isVertical) {
                    int pos = verticalLayoutManager.findFirstCompletelyVisibleItemPosition();
                    horizontalLayoutManager.scrollToPositionWithOffset(pos, 20);
                    Log.e("isVertical", "TRUE");
                    isHorizontal = false;
                } else {
                    isVertical = true;
                }*//*


            }
        });*/


    }
}

Adapter code

public class MyDataAdapter extends RecyclerView.Adapter {

    Context context;
    ArrayList arrayList;


    public MyDataAdapter(Context context, ArrayList arrayList) {
        this.context = context;
        this.arrayList = arrayList;
    }

    @Override
    public MyDataAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(context).inflate(R.layout.temp, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(MyDataAdapter.ViewHolder holder, int position) {

        if (position % 2 == 0) {
            holder.tvNumber.setBackgroundResource(R.color.colorGreen);
        } else {
            holder.tvNumber.setBackgroundResource(R.color.colorRed);
        }
        holder.tvNumber.setText(arrayList.get(position));
    }

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

    public class ViewHolder extends RecyclerView.ViewHolder {

        TextView tvNumber;

        public ViewHolder(View itemView) {
            super(itemView);
            tvNumber = itemView.findViewById(R.id.tvNumber);
        }
    }
}

Activity layout

temp Layout

COLOR

#307832
#ff4c4c