As the title says, the game won't let me place by custom slab on the bottom if top is already placed. Here is my custom slab class. I do have the CustomBlockHalfSlab and DoubleSlab classes as well. Thanks in advance

public abstract class CustomBlockSlab extends BlockSlab
{
	public CustomBlockSlab(String name, float hardness, float resistance)
	{
		super(Material.IRON);
		setUnlocalizedName(name);
		setRegistryName(name);
		setHardness(hardness);
		setResistance(resistance);
		
		this.fullBlock = this.isDouble();
		IBlockState state = this.blockState.getBaseState();
		
		if(!this.isDouble())
		{
			state = state.withProperty(HALF, EnumBlockHalf.BOTTOM);
		}
		
		setDefaultState(state);
		this.useNeighborBrightness = true;
	}
	
	@Override
	public String getUnlocalizedName(int meta) 
	{
		return this.getUnlocalizedName();
	}

	@Override
	public IProperty<?> getVariantProperty() 
	{
		return HALF;
	}
	
	@Override
	public Comparable<?> getTypeForItem(ItemStack stack)
	{
		return EnumBlockHalf.BOTTOM;
	}
	
	@Override
	public int damageDropped(IBlockState state) 
	{
		return 0;
	}
	
	@Override
	public IBlockState getStateFromMeta(int meta) 
	{
		if(!this.isDouble())
		{
			return this.getDefaultState().withProperty(HALF, EnumBlockHalf.values()[meta % EnumBlockHalf.values().length]);
		}
		return this.getDefaultState();
	}
	
	@Override
	public int getMetaFromState(IBlockState state) 
	{
		if(this.isDouble())
		{
			return 0;
		}
		
		return ((EnumBlockHalf)state.getValue(HALF)).ordinal() + 1;
	}
	
	@Override
	public Item getItemDropped(IBlockState state, Random rand, int fortune) 
	{
		return Item.getItemFromBlock(BlockInit.tutorial_slab_half);
	}
	
	@Override
	protected BlockStateContainer createBlockState() 
	{
		return new BlockStateContainer(this, new IProperty[] {HALF});
	}
	
	@Override
	public IBlockState getStateForPlacement(World world, BlockPos pos, EnumFacing facing, float hitX, float hitY, float hitZ, int meta, EntityLivingBase placer, EnumHand hand) 
	{
		return super.getStateForPlacement(world, pos, facing, hitX, hitY, hitZ, meta, placer, hand);
	}

 

What class are you using for the Item form of the slab? Vanilla uses ItemSlab, which handles combining single slabs into double slabs.

I use item slab

 

Block Init: 

tutorial_slab_half = new CustomBlockHalfSlab("tutorial_slab_half", 2.5F, 4.5F);
tutorial_slab_double = new CustomBlockDoubleSlab("tutorial_slab_double", 2.5F, 4.5F);

registerBlock(tutorial_slab_half, new ItemSlab(tutorial_slab_half, tutorial_slab_half, tutorial_slab_double));
ForgeRegistries.BLOCKS.register(tutorial_slab_double);

public static void registerBlock(Block block, ItemBlock itemblock)
	{
		ForgeRegistries.BLOCKS.register(block);
		block.setCreativeTab(TutorialMod.tutorialtab);
		itemblock.setRegistryName(block.getRegistryName());
		ForgeRegistries.ITEMS.register(itemblock);
		
		ModelLoader.setCustomModelResourceLocation(Item.getItemFromBlock(block), 0, new ModelResourceLocation(block.getRegistryName(), "inventory"));
	}

 

I'm not too sure what the problem is, then. Try setting a breakpoint in ItemSlab#onItemUse, clicking a top slab while holding a slab and stepping through the code to see why it's not combing the slabs.

 

Side note: ModelLoader is a client-only class, referencing it in common code will crash the dedicated server. Model registration must be handled in a dedicated, client-only class.

 

Registration of Blocks, Items and other IForgeRegistryEntry implementations should be done in the corresponding registry events. Registration of models should be done in ModelRegistryEvent. Pass Side.CLIENT to the @Mod.EventBusSubscriber annotation to prevent the model registration class being loaded on the dedicated server.

The game won't let me click a block with the item, so it's not called. The top slab seems to be blocking the full place box