mGridview.setOnItemClick(new OnItemClickListener() {
		
		@Override
		public void click(int index) {
			Log.d(TAG, "item : " + index + " -- clicked!");
		}
	});
    
    mGridview.setOnSwappingListener(new OnSwappingListener() {
		
		@Override
		public void waspping(int oldIndex, int newIndex) {
			Book book = books.get(oldIndex);
			books.remove(oldIndex);
			books.add(newIndex, book);
			
			adapter.notifyDataSetChanged();
		}
	});