code: public void attachTo(RecyclerView recycler, boolean headerAlreadyAligned) {
          validateRecycler(recycler, headerAlreadyAligned);
  
          mRecycler = recycler;
          mAlreadyAligned = headerAlreadyAligned;
          mReversed = isLayoutManagerReversed(recycler);
  
          setupAlignment(recycler);
          setupHeader(recycler);
  
  //        final TypedArray styledAttributes = getContext().getTheme().obtainStyledAttributes(
  //                new int[]{android.R.attr.actionBarSize});
  //        int mActionBarSize = (int) styledAttributes.getDimension(0, 0);
  //        styledAttributes.recycle();
  //        int height = mActionBarSize;
          recycler.addItemDecoration(new HeaderItemDecoration(this.getResources().getDrawable(R.drawable.divider),recycler.getLayoutManager(), 0), 0);
      }
docs: Attaches <code>RecyclerViewHeader</code> to <code>RecyclerView</code>.
  Be sure that <code>setLayoutManager(...)</code> has been called for <code>RecyclerView</code> before calling this method.
  Also, if you were planning to use <code>setOnScrollListener(...)</code> method for your <code>RecyclerView</code>, be sure to do it before calling this method.
  
  @param recycler             <code>RecyclerView</code> to attach <code>RecyclerViewHeader</code> to.
  @param headerAlreadyAligned If set to <code>false</code>, method will perform necessary actions to properly align
  the header within <code>RecyclerView</code>. If set to <code>true</code> method will assume,
  that user has already aligned <code>RecyclerViewHeader</code> properly.