two functions

@Override
public IBlockState getActualState(IBlockState state, IBlockAccess world, BlockPos pos)
{
    TileEntityBlockholeWall tile = (TileEntityBlockholeWall) (world instanceof ChunkCache ? ((ChunkCache)world).getTileEntity(pos,
                                   Chunk.EnumCreateEntityType.CHECK) : world.getTileEntity(pos));

    return state.withProperty(INDEX, tile.getIndex());
}

@Override
public void onBlockPlacedBy(World world, BlockPos pos, IBlockState state, EntityLivingBase placer, ItemStack stack)
{
    ((TileEntityBlockholeWall)world.getTileEntity(pos)).setIndex(0);
}