Sticky Header RecyclerView

SimpleRecyclerView.java

package com.saber.customstickyheader;

import android.graphics.Color;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

public class SimpleRecyclerView extends RecyclerView.Adapter<RecyclerView.ViewHolder> implements StickHeaderItemDecoration.StickyHeaderInterface {
    private List<Data> mData;

    public SimpleRecyclerView() {
        mData = new ArrayList<>();
        mData.add(new Data(1));
        mData.add(new Data(0));
        mData.add(new Data(0));
        mData.add(new Data(0));
        mData.add(new Data(0));`
        mData.add(new Data(0));
        mData.add(new Data(2));
        mData.add(new Data(0));
        mData.add(new Data(0));
        mData.add(new Data(0));
        mData.add(new Data(0));
        mData.add(new Data(0));
        mData.add(new Data(0));
        mData.add(new Data(1));
        mData.add(new Data(0));
        mData.add(new Data(0));
        mData.add(new Data(0));
        mData.add(new Data(0));
        mData.add(new Data(0));
        mData.add(new Data(0));
        mData.add(new Data(2));
        mData.add(new Data(0));
        mData.add(new Data(0));
        mData.add(new Data(0));
        mData.add(new Data(0));
        mData.add(new Data(0));
    }

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        switch (viewType) {
            case HeaderDataImpl.HEADER_TYPE_1:
                return new SimpleRecyclerView.HeaderViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.header1_item_recycler, parent, false));
            case HeaderDataImpl.HEADER_TYPE_2:
                return new SimpleRecyclerView.Header2ViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.header2_item_recycler, parent, false));
            default:
                return new SimpleRecyclerView.ViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item_recycler, parent, false));
        }
    }

    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
        if (holder instanceof ViewHolder) {
            ((ViewHolder) holder).bindData(position);
        } else if (holder instanceof HeaderViewHolder){
            ((HeaderViewHolder) holder).bindData(position);
        } else if (holder instanceof Header2ViewHolder){
            ((Header2ViewHolder) holder).bindData(position);
        }
    }

    @Override
    public int getItemViewType(int position) {
        return mData.get(position).getViewType();
    }

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

    @Override
    public int getHeaderPositionForItem(int itemPosition) {
        int headerPosition = 0;
        do {
            if (this.isHeader(itemPosition)) {
                headerPosition = itemPosition;
                break;
            }
            itemPosition -= 1;
        } while (itemPosition >= 0);
        return headerPosition;
    }

    @Override
    public int getHeaderLayout(int headerPosition) {
        if (mData.get(headerPosition).getViewType() == 1)
            return R.layout.header1_item_recycler;
        else {
            return R.layout.header2_item_recycler;
        }
    }

    @Override
    public void bindHeaderData(View header, int headerPosition) {

    }

    @Override
    public boolean isHeader(int itemPosition) {
        if (mData.get(itemPosition).getViewType() == 1 || mData.get(itemPosition).getViewType() == 2)
            return true;
        else
            return false;
    }

    class HeaderViewHolder extends RecyclerView.ViewHolder {
        TextView tvHeader;

        HeaderViewHolder(View itemView) {
            super(itemView);
            tvHeader = itemView.findViewById(R.id.tvHeader);
        }

        void bindData(int position) {
            tvHeader.setText(String.valueOf(position / 5));
        }
    }

    class Header2ViewHolder extends RecyclerView.ViewHolder {
        TextView tvHeader;

        Header2ViewHolder(View itemView) {
            super(itemView);
            tvHeader = itemView.findViewById(R.id.tvHeader);
        }

        void bindData(int position) {
            tvHeader.setText(String.valueOf(position / 5));
        }
    }

    class ViewHolder extends RecyclerView.ViewHolder {

        TextView tvRows;

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

        void bindData(int position) {
            tvRows.setText("saber" + position);
            ((ViewGroup) tvRows.getParent()).setBackgroundColor(Color.parseColor("#ffffff"));
        }
    }

    class Data {
        int viewType;

        public Data(int viewType) {
            this.viewType = viewType;
        }

        public int getViewType() {
            return viewType;
        }

        public void setViewType(int viewType) {
            this.viewType = viewType;
        }
    }
}

StickHeaderItemDecoration.java

package com.saber.customstickyheader;

import android.graphics.Canvas;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class StickHeaderItemDecoration extends RecyclerView.ItemDecoration {

    private StickyHeaderInterface mListener;
    private int mStickyHeaderHeight;

    public StickHeaderItemDecoration(@NonNull StickyHeaderInterface listener) {
        mListener = listener;
    }

    @Override
    public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDrawOver(c, parent, state);
        View topChild = parent.getChildAt(0);
        if (topChild == null) {
            return;
        }

        int topChildPosition = parent.getChildAdapterPosition(topChild);
        if (topChildPosition == RecyclerView.NO_POSITION) {
            return;
        }

        int headerPos = mListener.getHeaderPositionForItem(topChildPosition);
        View currentHeader = getHeaderViewForItem(headerPos, parent);
        fixLayoutSize(parent, currentHeader);
        int contactPoint = currentHeader.getBottom();
        View childInContact = getChildInContact(parent, contactPoint, headerPos);

        if (childInContact != null && mListener.isHeader(parent.getChildAdapterPosition(childInContact))) {
            moveHeader(c, currentHeader, childInContact);
            return;
        }

        drawHeader(c, currentHeader);
    }

    private View getHeaderViewForItem(int headerPosition, RecyclerView parent) {
        int layoutResId = mListener.getHeaderLayout(headerPosition);
        View header = LayoutInflater.from(parent.getContext()).inflate(layoutResId, parent, false);
        mListener.bindHeaderData(header, headerPosition);
        return header;
    }

    private void drawHeader(Canvas c, View header) {
        c.save();
        c.translate(0,  0);
        header.draw(c);
        c.restore();
    }

    private void moveHeader(Canvas c, View currentHeader, View nextHeader) {
        c.save();
        c.translate(0, nextHeader.getTop() - currentHeader.getHeight());
        currentHeader.draw(c);
        c.restore();
    }

    private View getChildInContact(RecyclerView parent, int contactPoint, int currentHeaderPos) {
        View childInContact = null;
        for (int i = 0; i < parent.getChildCount(); i++) {
            int heightTolerance = 0;
            View child = parent.getChildAt(i);

            //measure height tolerance with child if child is another header
            if (currentHeaderPos != i) {
                boolean isChildHeader = mListener.isHeader(parent.getChildAdapterPosition(child));
                if (isChildHeader) {
                    heightTolerance = mStickyHeaderHeight - child.getHeight();
                }
            }

            //add heightTolerance if child top be in display area
            int childBottomPosition;
            if (child.getTop() > 0) {
                childBottomPosition = child.getBottom() + heightTolerance;
            } else {
                childBottomPosition = child.getBottom();
            }

            if (childBottomPosition > contactPoint) {
                if (child.getTop() <= contactPoint) {
                    // This child overlaps the contactPoint
                    childInContact = child;
                    break;
                }
            }
        }
        return childInContact;
    }


    /**
     * Properly measures and layouts the top sticky header.
     * @param parent ViewGroup: RecyclerView in this case.
     */
    private void fixLayoutSize(ViewGroup parent, View view) {

        // Specs for parent (RecyclerView)
        int widthSpec = View.MeasureSpec.makeMeasureSpec(parent.getWidth(), View.MeasureSpec.EXACTLY);
        int heightSpec = View.MeasureSpec.makeMeasureSpec(parent.getHeight(), View.MeasureSpec.UNSPECIFIED);

        // Specs for children (headers)
        int childWidthSpec = ViewGroup.getChildMeasureSpec(widthSpec, parent.getPaddingLeft() + parent.getPaddingRight(), view.getLayoutParams().width);
        int childHeightSpec = ViewGroup.getChildMeasureSpec(heightSpec, parent.getPaddingTop() + parent.getPaddingBottom(), view.getLayoutParams().height);

        view.measure(childWidthSpec, childHeightSpec);

        view.layout(0, 0, view.getMeasuredWidth(), mStickyHeaderHeight = view.getMeasuredHeight());
    }

    public interface StickyHeaderInterface {

        /**
         * This method gets called by {@link StickHeaderItemDecoration} to fetch the position of the header item in the adapter
         * that is used for (represents) item at specified position.
         * @param itemPosition int. Adapter's position of the item for which to do the search of the position of the header item.
         * @return int. Position of the header item in the adapter.
         */
        int getHeaderPositionForItem(int itemPosition);

        /**
         * This method gets called by {@link StickHeaderItemDecoration} to get layout resource id for the header item at specified adapter's position.
         * @param headerPosition int. Position of the header item in the adapter.
         * @return int. Layout resource id.
         */
        int getHeaderLayout(int headerPosition);

        /**
         * This method gets called by {@link StickHeaderItemDecoration} to setup the header View.
         * @param header View. Header to set the data on.
         * @param headerPosition int. Position of the header item in the adapter.
         */
        void bindHeaderData(View header, int headerPosition);

        /**
         * This method gets called by {@link StickHeaderItemDecoration} to verify whether the item represents a header.
         * @param itemPosition int.
         * @return true, if item at the specified adapter's position represents a header.
         */
        boolean isHeader(int itemPosition);
    }
}

your activity or fragment

RecyclerView recyclerView = findViewById(R.id.recyclerView);
SimpleRecyclerView adapter = new SimpleRecyclerView();
LinearLayoutManager layoutManager = new LinearLayoutManager(this);

recyclerView.setAdapter(adapter);
recyclerView.setLayoutManager(layoutManager);
recyclerView.addItemDecoration(new StickHeaderItemDecoration(adapter));