I'm just curious, is it actually possible to modify the ExtendedBlockState after it is created? I've tried to do the following:

In The Block Class:

@Override
    public boolean onBlockActivated(World worldIn, BlockPos pos, IBlockState state, EntityPlayer playerIn, EnumFacing side, float hitX, float hitY, float hitZ) {
        if(state instanceof IExtendedBlockState){
            System.out.println(((IExtendedBlockState)state).getValue(BlockStateProperties.unlistedBlockPos);
        }
        return true;
    }

@Override
    public void onBlockPlacedBy(World worldIn, BlockPos pos, IBlockState state, EntityLivingBase placer, ItemStack stack) {
        if(state instanceof IExtendedBlockState){
            state = ((IExtendedBlockState)state).withProperty(BlockStateProperties.unlistedBlockPos, pos);
        }
        worldIn.setBlockState(pos, state, 3);
    }

@Override
    public IBlockState getExtendedState(IBlockState state, IBlockAccess world, BlockPos pos) {
        if(state instanceof IExtendedBlockState){
            return ((IExtendedBlockState)state).withProperty(BlockStateProperties.unlistedBlockPos, pos);
        }
        return state;
    }

@Override
    protected BlockState createBlockState() {
        return new ExtendedBlockState(this, new IProperty[]{BlockStateProperties.FACING}, new IUnlistedProperty[]{BlockStateProperties.unlistedBlockPos});
    }

 

When I call worldIn.setBlockState(pos, state, 3) and the state is a ExtendedBlockState the Block will be placed and removed just right after. But even if I don't set it and just try to access the value, it allways return null.

 

The unliestedBlockPos is just a unlisted Property that will Keep a BlockPos:

public static final IUnlistedProperty<BlockPos> unlistedBlockPos = new IUnlistedProperty<BlockPos>() {
        @Override
        public String getName() {
            return "unlistedBlockPos";
        }

        @Override
        public boolean isValid(BlockPos value) {
            return true;
        }

        @Override
        public Class<BlockPos> getType() {
            return BlockPos.class;
        }

        @Override
        public String valueToString(BlockPos value) {
            return value.toLong()+"";
        }
    };

 

Is it actually no way to access the ExtendedBlockState, or is something missing?

Ok, so I have to go with a TileEntity then, thanks for the reply !