RecyclerView GridLayoutManager with full width header

Try with this:

mLayoutManager = new GridLayoutManager(this, 2);
        mLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
            @Override
            public int getSpanSize(int position) {
                switch(mAdapter.getItemViewType(position)){
                    case MyAdapter.HEADER:
                        return 2;

                    case MyAdapter.ITEM:
                    default:
                        return 1;
                }
            }
        });

And check these links:

• RecyclerView: Grid with header
• Set span for items in GridLayoutManager using SpanSizeLookup