Android-sticky-recycler-view.java

public class SnStickyHeaderItemDecoration extends RecyclerView.ItemDecoration {

    private SnStickyListener mListener;
    private Integer mHeaderHeight;

    public SnStickyHeaderItemDecoration(SnStickyListener listener) {
        this.mListener = listener;
    }

    @Override
    public void onDrawOver(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull 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 = mHeaderHeight - 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(), mHeaderHeight = view.getMeasuredHeight());
    }

}

/////////////////////////////////////////////////////////////////////////////////////////////

public interface SnStickyListener {

    Integer getHeaderPositionForItem(Integer itemPosition);

    Integer getHeaderLayout(Integer headerPosition);

    void bindHeaderData(View header, Integer headerPosition);

    Boolean isHeader(Integer itemPosition);
}

///////////////////////////////////////////////////////////////////////////////////////////////
public class DepositLogsAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> implements SnStickyListener {

    private Context context;
    static final int TYPE_HEADER = 0;
    static final int TYPE_ITEM = 1;

    public DepositLogsAdapter(Context context) {
        this.context = context;
    }

    @Override
    public int getItemViewType(int position) {

        return position % 5 == 0 ? TYPE_HEADER : TYPE_ITEM;
    }

    @Override
    public Integer getHeaderPositionForItem(Integer itemPosition) {
        Integer headerPosition = 0;
        for (Integer i = itemPosition; i > 0; i--) {
            if (isHeader(i)) {
                headerPosition = i;
                return headerPosition;
            }
        }
        return headerPosition;
    }

    @Override
    public Integer getHeaderLayout(Integer headerPosition) {
        return R.layout.deposit_log_header_view;
    }

    @Override
    public void bindHeaderData(View headerView, Integer headerPosition) {
        // bind data to header view.....
    }

    @Override
    public Boolean isHeader(Integer itemPosition) {
        return itemPosition % 5 == 0;
    }


    class ItemView extends RecyclerView.ViewHolder {

        ItemView(View itemView) {
            super(itemView);
        }

    }

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        if (viewType == TYPE_ITEM) {
            View view = LayoutInflater.from(context).inflate(R.layout.deposit_log_item_view, parent, false);
            return new ItemView(view);
        } else {
            View view = LayoutInflater.from(context).inflate(R.layout.deposit_log_header_view, parent, false);
            return new ItemView(view);
        }
    }

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

    }

    @Override
    public int getItemCount() {
        return 25;
    }
}

// END